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<li><a class="reference internal" href="#">6. Expressions</a><ul>
<li><a class="reference internal" href="#arithmetic-conversions">6.1. Arithmetic conversions</a></li>
<li><a class="reference internal" href="#atoms">6.2. Atoms</a><ul>
<li><a class="reference internal" href="#built-in-constants">6.2.1. Built-in constants</a></li>
<li><a class="reference internal" href="#atom-identifiers">6.2.2. Identifiers (Names)</a><ul>
<li><a class="reference internal" href="#index-5">6.2.2.1. Private name mangling</a></li>
</ul>
</li>
<li><a class="reference internal" href="#literals">6.2.3. Literals</a><ul>
<li><a class="reference internal" href="#literals-and-object-identity">6.2.3.1. Literals and object identity</a></li>
<li><a class="reference internal" href="#string-literal-concatenation">6.2.3.2. String literal concatenation</a></li>
</ul>
</li>
<li><a class="reference internal" href="#parenthesized-forms">6.2.4. Parenthesized forms</a></li>
<li><a class="reference internal" href="#displays-for-lists-sets-and-dictionaries">6.2.5. Displays for lists, sets and dictionaries</a></li>
<li><a class="reference internal" href="#list-displays">6.2.6. List displays</a></li>
<li><a class="reference internal" href="#set-displays">6.2.7. Set displays</a></li>
<li><a class="reference internal" href="#dictionary-displays">6.2.8. Dictionary displays</a></li>
<li><a class="reference internal" href="#generator-expressions">6.2.9. Generator expressions</a></li>
<li><a class="reference internal" href="#yield-expressions">6.2.10. Yield expressions</a><ul>
<li><a class="reference internal" href="#generator-iterator-methods">6.2.10.1. Generator-iterator methods</a></li>
<li><a class="reference internal" href="#examples">6.2.10.2. Examples</a></li>
<li><a class="reference internal" href="#asynchronous-generator-functions">6.2.10.3. Asynchronous generator functions</a></li>
<li><a class="reference internal" href="#asynchronous-generator-iterator-methods">6.2.10.4. Asynchronous generator-iterator methods</a></li>
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</li>
<li><a class="reference internal" href="#primaries">6.3. Primaries</a><ul>
<li><a class="reference internal" href="#attribute-references">6.3.1. Attribute references</a></li>
<li><a class="reference internal" href="#subscriptions-and-slicings">6.3.2. Subscriptions and slicings</a><ul>
<li><a class="reference internal" href="#slicings">6.3.2.1. Slicings</a></li>
<li><a class="reference internal" href="#comma-separated-subscripts">6.3.2.2. Comma-separated subscripts</a></li>
<li><a class="reference internal" href="#starred-subscriptions">6.3.2.3. “Starred” subscriptions</a></li>
<li><a class="reference internal" href="#formal-subscription-grammar">6.3.2.4. Formal subscription grammar</a></li>
</ul>
</li>
<li><a class="reference internal" href="#calls">6.3.3. Calls</a></li>
</ul>
</li>
<li><a class="reference internal" href="#await-expression">6.4. Await expression</a></li>
<li><a class="reference internal" href="#the-power-operator">6.5. The power operator</a></li>
<li><a class="reference internal" href="#unary-arithmetic-and-bitwise-operations">6.6. Unary arithmetic and bitwise operations</a></li>
<li><a class="reference internal" href="#binary-arithmetic-operations">6.7. Binary arithmetic operations</a></li>
<li><a class="reference internal" href="#shifting-operations">6.8. Shifting operations</a></li>
<li><a class="reference internal" href="#binary-bitwise-operations">6.9. Binary bitwise operations</a></li>
<li><a class="reference internal" href="#comparisons">6.10. Comparisons</a><ul>
<li><a class="reference internal" href="#value-comparisons">6.10.1. Value comparisons</a></li>
<li><a class="reference internal" href="#membership-test-operations">6.10.2. Membership test operations</a></li>
<li><a class="reference internal" href="#is-not">6.10.3. Identity comparisons</a></li>
</ul>
</li>
<li><a class="reference internal" href="#boolean-operations">6.11. Boolean operations</a></li>
<li><a class="reference internal" href="#assignment-expressions">6.12. Assignment expressions</a></li>
<li><a class="reference internal" href="#conditional-expressions">6.13. Conditional expressions</a></li>
<li><a class="reference internal" href="#lambda">6.14. Lambdas</a></li>
<li><a class="reference internal" href="#expression-lists">6.15. Expression lists</a></li>
<li><a class="reference internal" href="#evaluation-order">6.16. Evaluation order</a></li>
<li><a class="reference internal" href="#operator-precedence">6.17. Operator precedence</a></li>
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  <section id="expressions">
<span id="id1"></span><h1><span class="section-number">6. </span>Expressions<a class="headerlink" href="#expressions" title="Link to this heading">¶</a></h1>
<p id="index-0">This chapter explains the meaning of the elements of expressions in Python.</p>
<p><strong>Syntax Notes:</strong> In this and the following chapters,
<a class="reference internal" href="introduction.html#notation"><span class="std std-ref">grammar notation</span></a> will be used to describe syntax,
not lexical analysis.</p>
<p>When (one alternative of) a syntax rule has the form:</p>
<pre class="highlight">
<strong id="grammar-token-python-grammar-name">name</strong>: othername
</pre>
<p>and no semantics are given, the semantics of this form of <code class="docutils literal notranslate"><span class="pre">name</span></code> are the same
as for <code class="docutils literal notranslate"><span class="pre">othername</span></code>.</p>
<section id="arithmetic-conversions">
<span id="conversions"></span><h2><span class="section-number">6.1. </span>Arithmetic conversions<a class="headerlink" href="#arithmetic-conversions" title="Link to this heading">¶</a></h2>
<p id="index-1">When a description of an arithmetic operator below uses the phrase “the numeric
arguments are converted to a common real type”, this means that the operator
implementation for built-in numeric types works as described in the
<a class="reference internal" href="../library/stdtypes.html#stdtypes-mixed-arithmetic"><span class="std std-ref">Numeric Types</span></a> section of the standard
library documentation.</p>
<p>Some additional rules apply for certain operators and non-numeric operands
(for example, a string as a left argument to the <code class="docutils literal notranslate"><span class="pre">%</span></code> operator).
Extensions must define their own conversion behavior.</p>
</section>
<section id="atoms">
<span id="id2"></span><h2><span class="section-number">6.2. </span>Atoms<a class="headerlink" href="#atoms" title="Link to this heading">¶</a></h2>
<p id="index-2">Atoms are the most basic elements of expressions.
The simplest atoms are <a class="reference internal" href="lexical_analysis.html#identifiers"><span class="std std-ref">names</span></a> or literals.
Forms enclosed in parentheses, brackets or braces are also categorized
syntactically as atoms.</p>
<p>Formally, the syntax for atoms is:</p>
<pre class="highlight">
<strong id="grammar-token-python-grammar-atom">atom</strong>:
   | <span class="sx">'True'</span>
   | <span class="sx">'False'</span>
   | <span class="sx">'None'</span>
   | <span class="sx">'...'</span>
   | <a class="reference internal" href="lexical_analysis.html#grammar-token-python-grammar-identifier"><code class="xref docutils literal notranslate"><span class="pre">identifier</span></code></a>
   | <a class="reference internal" href="#grammar-token-python-grammar-literal"><code class="xref docutils literal notranslate"><span class="pre">literal</span></code></a>
   | <a class="reference internal" href="#grammar-token-python-grammar-enclosure"><code class="xref docutils literal notranslate"><span class="pre">enclosure</span></code></a>
<strong id="grammar-token-python-grammar-enclosure">enclosure</strong>:
   | <a class="reference internal" href="#grammar-token-python-grammar-parenth_form"><code class="xref docutils literal notranslate"><span class="pre">parenth_form</span></code></a>
   | <a class="reference internal" href="#grammar-token-python-grammar-list_display"><code class="xref docutils literal notranslate"><span class="pre">list_display</span></code></a>
   | <a class="reference internal" href="#grammar-token-python-grammar-dict_display"><code class="xref docutils literal notranslate"><span class="pre">dict_display</span></code></a>
   | <a class="reference internal" href="#grammar-token-python-grammar-set_display"><code class="xref docutils literal notranslate"><span class="pre">set_display</span></code></a>
   | <a class="reference internal" href="#grammar-token-python-grammar-generator_expression"><code class="xref docutils literal notranslate"><span class="pre">generator_expression</span></code></a>
   | <a class="reference internal" href="#grammar-token-python-grammar-yield_atom"><code class="xref docutils literal notranslate"><span class="pre">yield_atom</span></code></a>
</pre>
<section id="built-in-constants">
<span id="atom-singletons"></span><h3><span class="section-number">6.2.1. </span>Built-in constants<a class="headerlink" href="#built-in-constants" title="Link to this heading">¶</a></h3>
<p>The keywords <code class="docutils literal notranslate"><span class="pre">True</span></code>, <code class="docutils literal notranslate"><span class="pre">False</span></code>, and <code class="docutils literal notranslate"><span class="pre">None</span></code> name
<a class="reference internal" href="../library/constants.html#built-in-consts"><span class="std std-ref">built-in constants</span></a>.
The token <code class="docutils literal notranslate"><span class="pre">...</span></code> names the <a class="reference internal" href="../library/constants.html#Ellipsis" title="Ellipsis"><code class="xref py py-data docutils literal notranslate"><span class="pre">Ellipsis</span></code></a> constant.</p>
<p>Evaluation of these atoms yields the corresponding value.</p>
<div class="admonition note">
<p class="admonition-title">Note</p>
<p>Several more built-in constants are available as global variables,
but only the ones mentioned here are <a class="reference internal" href="lexical_analysis.html#keywords"><span class="std std-ref">keywords</span></a>.
In particular, these names cannot be reassigned or used as attributes:</p>
<div class="highlight-pycon notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="kc">False</span> <span class="o">=</span> <span class="mi">123</span>
  File <span class="nb">&quot;&lt;input&gt;&quot;</span>, line <span class="m">1</span>
<span class="gr">   False = 123</span>
<span class="gr">   ^^^^^</span>
<span class="gr">SyntaxError</span>: <span class="n">cannot assign to False</span>
</pre></div>
</div>
</div>
</section>
<section id="atom-identifiers">
<span id="identifiers-names"></span><h3><span class="section-number">6.2.2. </span>Identifiers (Names)<a class="headerlink" href="#atom-identifiers" title="Link to this heading">¶</a></h3>
<p id="index-3">An identifier occurring as an atom is a name.  See section <a class="reference internal" href="lexical_analysis.html#identifiers"><span class="std std-ref">Names (identifiers and keywords)</span></a>
for lexical definition and section <a class="reference internal" href="executionmodel.html#naming"><span class="std std-ref">Naming and binding</span></a> for documentation of naming and
binding.</p>
<p id="index-4">When the name is bound to an object, evaluation of the atom yields that object.
When a name is not bound, an attempt to evaluate it raises a <a class="reference internal" href="../library/exceptions.html#NameError" title="NameError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">NameError</span></code></a>
exception.</p>
<section id="index-5">
<span id="private-name-mangling"></span><span id="id3"></span><h4><span class="section-number">6.2.2.1. </span>Private name mangling<a class="headerlink" href="#index-5" title="Link to this heading">¶</a></h4>
<p>When an identifier that textually occurs in a class definition begins with two
or more underscore characters and does not end in two or more underscores, it
is considered a <em class="dfn">private name</em> of that class.</p>
<div class="admonition seealso">
<p class="admonition-title">See also</p>
<p>The <a class="reference internal" href="compound_stmts.html#class"><span class="std std-ref">class specifications</span></a>.</p>
</div>
<p>More precisely, private names are transformed to a longer form before code is
generated for them.  If the transformed name is longer than 255 characters,
implementation-defined truncation may happen.</p>
<p>The transformation is independent of the syntactical context in which the
identifier is used but only the following private identifiers are mangled:</p>
<ul>
<li><p>Any name used as the name of a variable that is assigned or read or any
name of an attribute being accessed.</p>
<p>The <a class="reference internal" href="../library/stdtypes.html#definition.__name__" title="definition.__name__"><code class="xref py py-attr docutils literal notranslate"><span class="pre">__name__</span></code></a> attribute of nested functions, classes, and
type aliases is however not mangled.</p>
</li>
<li><p>The name of imported modules, e.g., <code class="docutils literal notranslate"><span class="pre">__spam</span></code> in <code class="docutils literal notranslate"><span class="pre">import</span> <span class="pre">__spam</span></code>.
If the module is part of a package (i.e., its name contains a dot),
the name is <em>not</em> mangled, e.g., the <code class="docutils literal notranslate"><span class="pre">__foo</span></code> in <code class="docutils literal notranslate"><span class="pre">import</span> <span class="pre">__foo.bar</span></code>
is not mangled.</p></li>
<li><p>The name of an imported member, e.g., <code class="docutils literal notranslate"><span class="pre">__f</span></code> in <code class="docutils literal notranslate"><span class="pre">from</span> <span class="pre">spam</span> <span class="pre">import</span> <span class="pre">__f</span></code>.</p></li>
</ul>
<p>The transformation rule is defined as follows:</p>
<ul class="simple">
<li><p>The class name, with leading underscores removed and a single leading
underscore inserted, is inserted in front of the identifier, e.g., the
identifier <code class="docutils literal notranslate"><span class="pre">__spam</span></code> occurring in a class named <code class="docutils literal notranslate"><span class="pre">Foo</span></code>, <code class="docutils literal notranslate"><span class="pre">_Foo</span></code> or
<code class="docutils literal notranslate"><span class="pre">__Foo</span></code> is transformed to <code class="docutils literal notranslate"><span class="pre">_Foo__spam</span></code>.</p></li>
<li><p>If the class name consists only of underscores, the transformation is the
identity, e.g., the identifier <code class="docutils literal notranslate"><span class="pre">__spam</span></code> occurring in a class named <code class="docutils literal notranslate"><span class="pre">_</span></code>
or <code class="docutils literal notranslate"><span class="pre">__</span></code> is left as is.</p></li>
</ul>
</section>
</section>
<section id="literals">
<span id="atom-literals"></span><h3><span class="section-number">6.2.3. </span>Literals<a class="headerlink" href="#literals" title="Link to this heading">¶</a></h3>
<p id="index-6">A <em class="dfn">literal</em> is a textual representation of a value.
Python supports numeric, string and bytes literals.
<a class="reference internal" href="lexical_analysis.html#f-strings"><span class="std std-ref">Format strings</span></a> and <a class="reference internal" href="lexical_analysis.html#t-strings"><span class="std std-ref">template strings</span></a>
are treated as string literals.</p>
<p>Numeric literals consist of a single <a class="reference internal" href="lexical_analysis.html#grammar-token-python-grammar-NUMBER"><code class="xref std std-token docutils literal notranslate"><span class="pre">NUMBER</span></code></a>
token, which names an integer, floating-point number, or an imaginary number.
See the <a class="reference internal" href="lexical_analysis.html#numbers"><span class="std std-ref">Numeric literals</span></a> section in Lexical analysis documentation for details.</p>
<p>String and bytes literals may consist of several tokens.
See section <a class="reference internal" href="#string-concatenation"><span class="std std-ref">String literal concatenation</span></a> for details.</p>
<p>Note that negative and complex numbers, like <code class="docutils literal notranslate"><span class="pre">-3</span></code> or <code class="docutils literal notranslate"><span class="pre">3+4.2j</span></code>,
are syntactically not literals, but <a class="reference internal" href="#unary"><span class="std std-ref">unary</span></a> or
<a class="reference internal" href="#binary"><span class="std std-ref">binary</span></a> arithmetic operations involving the <code class="docutils literal notranslate"><span class="pre">-</span></code> or <code class="docutils literal notranslate"><span class="pre">+</span></code>
operator.</p>
<p>Evaluation of a literal yields an object of the given type
(<a class="reference internal" href="../library/functions.html#int" title="int"><code class="xref py py-class docutils literal notranslate"><span class="pre">int</span></code></a>, <a class="reference internal" href="../library/functions.html#float" title="float"><code class="xref py py-class docutils literal notranslate"><span class="pre">float</span></code></a>, <a class="reference internal" href="../library/functions.html#complex" title="complex"><code class="xref py py-class docutils literal notranslate"><span class="pre">complex</span></code></a>, <a class="reference internal" href="../library/stdtypes.html#str" title="str"><code class="xref py py-class docutils literal notranslate"><span class="pre">str</span></code></a>,
<a class="reference internal" href="../library/stdtypes.html#bytes" title="bytes"><code class="xref py py-class docutils literal notranslate"><span class="pre">bytes</span></code></a>, or <a class="reference internal" href="../library/string.templatelib.html#string.templatelib.Template" title="string.templatelib.Template"><code class="xref py py-class docutils literal notranslate"><span class="pre">Template</span></code></a>) with the given value.
The value may be approximated in the case of floating-point
and imaginary literals.</p>
<p>The formal grammar for literals is:</p>
<pre class="highlight">
<strong id="grammar-token-python-grammar-literal">literal</strong>: <a class="reference internal" href="#grammar-token-python-grammar-strings"><code class="xref docutils literal notranslate"><span class="pre">strings</span></code></a> | <a class="reference internal" href="lexical_analysis.html#grammar-token-python-grammar-NUMBER"><code class="xref docutils literal notranslate"><span class="pre">NUMBER</span></code></a>
</pre>
<section id="literals-and-object-identity">
<span id="index-7"></span><h4><span class="section-number">6.2.3.1. </span>Literals and object identity<a class="headerlink" href="#literals-and-object-identity" title="Link to this heading">¶</a></h4>
<p>All literals correspond to immutable data types, and hence the object’s identity
is less important than its value.  Multiple evaluations of literals with the
same value (either the same occurrence in the program text or a different
occurrence) may obtain the same object or a different object with the same
value.</p>
<div class="admonition-cpython-implementation-detail admonition">
<p class="admonition-title">CPython implementation detail</p>
<p>For example, in CPython, <em>small</em> integers with the same value evaluate
to the same object:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="n">x</span> <span class="o">=</span> <span class="mi">7</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">y</span> <span class="o">=</span> <span class="mi">7</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">x</span> <span class="ow">is</span> <span class="n">y</span>
<span class="go">True</span>
</pre></div>
</div>
<p>However, large integers evaluate to different objects:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="n">x</span> <span class="o">=</span> <span class="mi">123456789</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">y</span> <span class="o">=</span> <span class="mi">123456789</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">x</span> <span class="ow">is</span> <span class="n">y</span>
<span class="go">False</span>
</pre></div>
</div>
<p>This behavior may change in future versions of CPython.
In particular, the boundary between “small” and “large” integers has
already changed in the past.</p>
<p>CPython will emit a <a class="reference internal" href="../library/exceptions.html#SyntaxWarning" title="SyntaxWarning"><code class="xref py py-exc docutils literal notranslate"><span class="pre">SyntaxWarning</span></code></a> when you compare literals
using <code class="docutils literal notranslate"><span class="pre">is</span></code>:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="n">x</span> <span class="o">=</span> <span class="mi">7</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">x</span> <span class="ow">is</span> <span class="mi">7</span>
<span class="go">&lt;input&gt;:1: SyntaxWarning: &quot;is&quot; with &#39;int&#39; literal. Did you mean &quot;==&quot;?</span>
<span class="go">True</span>
</pre></div>
</div>
<p>See <a class="reference internal" href="../faq/programming.html#faq-identity-with-is"><span class="std std-ref">When can I rely on identity tests with the is operator?</span></a> for more information.</p>
</div>
<p><a class="reference internal" href="lexical_analysis.html#t-strings"><span class="std std-ref">Template strings</span></a> are immutable but may reference mutable
objects as <a class="reference internal" href="../library/string.templatelib.html#string.templatelib.Interpolation" title="string.templatelib.Interpolation"><code class="xref py py-class docutils literal notranslate"><span class="pre">Interpolation</span></code></a> values.
For the purposes of this section, two t-strings have the “same value” if
both their structure and the <em>identity</em> of the values match.</p>
<div class="impl-detail compound">
<p><strong>CPython implementation detail:</strong> Currently, each evaluation of a template string results in
a different object.</p>
</div>
</section>
<section id="string-literal-concatenation">
<span id="string-concatenation"></span><h4><span class="section-number">6.2.3.2. </span>String literal concatenation<a class="headerlink" href="#string-literal-concatenation" title="Link to this heading">¶</a></h4>
<p>Multiple adjacent string or bytes literals, possibly
using different quoting conventions, are allowed, and their meaning is the same
as their concatenation:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="s2">&quot;hello&quot;</span> <span class="s1">&#39;world&#39;</span>
<span class="go">&quot;helloworld&quot;</span>
</pre></div>
</div>
<p>This feature is defined at the syntactical level, so it only works with literals.
To concatenate string expressions at run time, the ‘+’ operator may be used:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="n">greeting</span> <span class="o">=</span> <span class="s2">&quot;Hello&quot;</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">space</span> <span class="o">=</span> <span class="s2">&quot; &quot;</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">name</span> <span class="o">=</span> <span class="s2">&quot;Blaise&quot;</span>
<span class="gp">&gt;&gt;&gt; </span><span class="nb">print</span><span class="p">(</span><span class="n">greeting</span> <span class="o">+</span> <span class="n">space</span> <span class="o">+</span> <span class="n">name</span><span class="p">)</span>   <span class="c1"># not: print(greeting space name)</span>
<span class="go">Hello Blaise</span>
</pre></div>
</div>
<p>Literal concatenation can freely mix raw strings, triple-quoted strings,
and formatted string literals.
For example:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="s2">&quot;Hello&quot;</span> <span class="sa">r</span><span class="s1">&#39;, &#39;</span> <span class="sa">f</span><span class="s2">&quot;</span><span class="si">{</span><span class="n">name</span><span class="si">}</span><span class="s2">!&quot;</span>
<span class="go">&quot;Hello, Blaise!&quot;</span>
</pre></div>
</div>
<p>This feature can be used to reduce the number of backslashes
needed, to split long strings conveniently across long lines, or even to add
comments to parts of strings. For example:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="n">re</span><span class="o">.</span><span class="n">compile</span><span class="p">(</span><span class="s2">&quot;[A-Za-z_]&quot;</span>       <span class="c1"># letter or underscore</span>
           <span class="s2">&quot;[A-Za-z0-9_]*&quot;</span>   <span class="c1"># letter, digit or underscore</span>
          <span class="p">)</span>
</pre></div>
</div>
<p>However, bytes literals may only be combined with other byte literals;
not with string literals of any kind.
Also, template string literals may only be combined with other template
string literals:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="sa">t</span><span class="s2">&quot;Hello&quot;</span> <span class="sa">t</span><span class="s2">&quot;</span><span class="si">{</span><span class="n">name</span><span class="si">}</span><span class="s2">!&quot;</span>
<span class="go">Template(strings=(&#39;Hello&#39;, &#39;!&#39;), interpolations=(...))</span>
</pre></div>
</div>
<p>Formally:</p>
<pre class="highlight">
<strong id="grammar-token-python-grammar-strings">strings</strong>: (<a class="reference internal" href="lexical_analysis.html#grammar-token-python-grammar-STRING"><code class="xref docutils literal notranslate"><span class="pre">STRING</span></code></a> | <a class="reference internal" href="lexical_analysis.html#grammar-token-python-grammar-fstring"><code class="xref docutils literal notranslate"><span class="pre">fstring</span></code></a>)+ | <a class="reference internal" href="lexical_analysis.html#grammar-token-python-grammar-tstring"><code class="xref docutils literal notranslate"><span class="pre">tstring</span></code></a>+
</pre>
</section>
</section>
<section id="parenthesized-forms">
<span id="parenthesized"></span><h3><span class="section-number">6.2.4. </span>Parenthesized forms<a class="headerlink" href="#parenthesized-forms" title="Link to this heading">¶</a></h3>
<p id="index-8">A parenthesized form is an optional expression list enclosed in parentheses:</p>
<pre class="highlight">
<strong id="grammar-token-python-grammar-parenth_form">parenth_form</strong>: <span class="sx">&quot;(&quot;</span> [<a class="reference internal" href="#grammar-token-python-grammar-starred_expression"><code class="xref docutils literal notranslate"><span class="pre">starred_expression</span></code></a>] <span class="sx">&quot;)&quot;</span>
</pre>
<p>A parenthesized expression list yields whatever that expression list yields: if
the list contains at least one comma, it yields a tuple; otherwise, it yields
the single expression that makes up the expression list.</p>
<p id="index-9">An empty pair of parentheses yields an empty tuple object.  Since tuples are
immutable, the same rules as for literals apply (i.e., two occurrences of the empty
tuple may or may not yield the same object).</p>
<p id="index-10">Note that tuples are not formed by the parentheses, but rather by use of the
comma.  The exception is the empty tuple, for which parentheses <em>are</em>
required — allowing unparenthesized “nothing” in expressions would cause
ambiguities and allow common typos to pass uncaught.</p>
</section>
<section id="displays-for-lists-sets-and-dictionaries">
<span id="comprehensions"></span><h3><span class="section-number">6.2.5. </span>Displays for lists, sets and dictionaries<a class="headerlink" href="#displays-for-lists-sets-and-dictionaries" title="Link to this heading">¶</a></h3>
<p id="index-11">For constructing a list, a set or a dictionary Python provides special syntax
called “displays”, each of them in two flavors:</p>
<ul class="simple">
<li><p>either the container contents are listed explicitly, or</p></li>
<li><p>they are computed via a set of looping and filtering instructions, called a
<em class="dfn">comprehension</em>.</p></li>
</ul>
<p id="index-12">Common syntax elements for comprehensions are:</p>
<pre class="highlight">
<strong id="grammar-token-python-grammar-comprehension">comprehension</strong>: <a class="reference internal" href="#grammar-token-python-grammar-assignment_expression"><code class="xref docutils literal notranslate"><span class="pre">assignment_expression</span></code></a> <a class="reference internal" href="#grammar-token-python-grammar-comp_for"><code class="xref docutils literal notranslate"><span class="pre">comp_for</span></code></a>
<strong id="grammar-token-python-grammar-comp_for">comp_for</strong>:      [<span class="sx">&quot;async&quot;</span>] <span class="sx">&quot;for&quot;</span> <a class="reference internal" href="simple_stmts.html#grammar-token-python-grammar-target_list"><code class="xref docutils literal notranslate"><span class="pre">target_list</span></code></a> <span class="sx">&quot;in&quot;</span> <a class="reference internal" href="#grammar-token-python-grammar-or_test"><code class="xref docutils literal notranslate"><span class="pre">or_test</span></code></a> [<a class="reference internal" href="#grammar-token-python-grammar-comp_iter"><code class="xref docutils literal notranslate"><span class="pre">comp_iter</span></code></a>]
<strong id="grammar-token-python-grammar-comp_iter">comp_iter</strong>:     <a class="reference internal" href="#grammar-token-python-grammar-comp_for"><code class="xref docutils literal notranslate"><span class="pre">comp_for</span></code></a> | <a class="reference internal" href="#grammar-token-python-grammar-comp_if"><code class="xref docutils literal notranslate"><span class="pre">comp_if</span></code></a>
<strong id="grammar-token-python-grammar-comp_if">comp_if</strong>:       <span class="sx">&quot;if&quot;</span> <a class="reference internal" href="#grammar-token-python-grammar-or_test"><code class="xref docutils literal notranslate"><span class="pre">or_test</span></code></a> [<a class="reference internal" href="#grammar-token-python-grammar-comp_iter"><code class="xref docutils literal notranslate"><span class="pre">comp_iter</span></code></a>]
</pre>
<p>The comprehension consists of a single expression followed by at least one
<code class="xref std std-keyword docutils literal notranslate"><span class="pre">for</span></code> clause and zero or more <code class="xref std std-keyword docutils literal notranslate"><span class="pre">for</span></code> or <code class="xref std std-keyword docutils literal notranslate"><span class="pre">if</span></code> clauses.
In this case, the elements of the new container are those that would be produced
by considering each of the <code class="xref std std-keyword docutils literal notranslate"><span class="pre">for</span></code> or <code class="xref std std-keyword docutils literal notranslate"><span class="pre">if</span></code> clauses a block,
nesting from left to right, and evaluating the expression to produce an element
each time the innermost block is reached.</p>
<p>However, aside from the iterable expression in the leftmost <code class="xref std std-keyword docutils literal notranslate"><span class="pre">for</span></code> clause,
the comprehension is executed in a separate implicitly nested scope. This ensures
that names assigned to in the target list don’t “leak” into the enclosing scope.</p>
<p>The iterable expression in the leftmost <code class="xref std std-keyword docutils literal notranslate"><span class="pre">for</span></code> clause is evaluated
directly in the enclosing scope and then passed as an argument to the implicitly
nested scope. Subsequent <code class="xref std std-keyword docutils literal notranslate"><span class="pre">for</span></code> clauses and any filter condition in the
leftmost <code class="xref std std-keyword docutils literal notranslate"><span class="pre">for</span></code> clause cannot be evaluated in the enclosing scope as
they may depend on the values obtained from the leftmost iterable. For example:
<code class="docutils literal notranslate"><span class="pre">[x*y</span> <span class="pre">for</span> <span class="pre">x</span> <span class="pre">in</span> <span class="pre">range(10)</span> <span class="pre">for</span> <span class="pre">y</span> <span class="pre">in</span> <span class="pre">range(x,</span> <span class="pre">x+10)]</span></code>.</p>
<p>To ensure the comprehension always results in a container of the appropriate
type, <code class="docutils literal notranslate"><span class="pre">yield</span></code> and <code class="docutils literal notranslate"><span class="pre">yield</span> <span class="pre">from</span></code> expressions are prohibited in the implicitly
nested scope.</p>
<p id="index-13">Since Python 3.6, in an <a class="reference internal" href="compound_stmts.html#async-def"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">async</span> <span class="pre">def</span></code></a> function, an <code class="xref std std-keyword docutils literal notranslate"><span class="pre">async</span> <span class="pre">for</span></code>
clause may be used to iterate over a <a class="reference internal" href="../glossary.html#term-asynchronous-iterator"><span class="xref std std-term">asynchronous iterator</span></a>.
A comprehension in an <code class="xref std std-keyword docutils literal notranslate"><span class="pre">async</span> <span class="pre">def</span></code> function may consist of either a
<code class="xref std std-keyword docutils literal notranslate"><span class="pre">for</span></code> or <code class="xref std std-keyword docutils literal notranslate"><span class="pre">async</span> <span class="pre">for</span></code> clause following the leading
expression, may contain additional <code class="xref std std-keyword docutils literal notranslate"><span class="pre">for</span></code> or <code class="xref std std-keyword docutils literal notranslate"><span class="pre">async</span> <span class="pre">for</span></code>
clauses, and may also use <a class="reference internal" href="#await"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">await</span></code></a> expressions.</p>
<p>If a comprehension contains <code class="xref std std-keyword docutils literal notranslate"><span class="pre">async</span> <span class="pre">for</span></code> clauses, or if it contains
<code class="xref std std-keyword docutils literal notranslate"><span class="pre">await</span></code> expressions or other asynchronous comprehensions anywhere except
the iterable expression in the leftmost <code class="xref std std-keyword docutils literal notranslate"><span class="pre">for</span></code> clause, it is called an
<em class="dfn">asynchronous comprehension</em>. An asynchronous comprehension may suspend the
execution of the coroutine function in which it appears.
See also <span class="target" id="index-14"></span><a class="pep reference external" href="https://peps.python.org/pep-0530/"><strong>PEP 530</strong></a>.</p>
<div class="versionadded">
<p><span class="versionmodified added">Added in version 3.6: </span>Asynchronous comprehensions were introduced.</p>
</div>
<div class="versionchanged">
<p><span class="versionmodified changed">Changed in version 3.8: </span><code class="docutils literal notranslate"><span class="pre">yield</span></code> and <code class="docutils literal notranslate"><span class="pre">yield</span> <span class="pre">from</span></code> prohibited in the implicitly nested scope.</p>
</div>
<div class="versionchanged">
<p><span class="versionmodified changed">Changed in version 3.11: </span>Asynchronous comprehensions are now allowed inside comprehensions in
asynchronous functions. Outer comprehensions implicitly become
asynchronous.</p>
</div>
</section>
<section id="list-displays">
<span id="lists"></span><h3><span class="section-number">6.2.6. </span>List displays<a class="headerlink" href="#list-displays" title="Link to this heading">¶</a></h3>
<p id="index-15">A list display is a possibly empty series of expressions enclosed in square
brackets:</p>
<pre class="highlight">
<strong id="grammar-token-python-grammar-list_display">list_display</strong>: <span class="sx">&quot;[&quot;</span> [<a class="reference internal" href="#grammar-token-python-grammar-flexible_expression_list"><code class="xref docutils literal notranslate"><span class="pre">flexible_expression_list</span></code></a> | <a class="reference internal" href="#grammar-token-python-grammar-comprehension"><code class="xref docutils literal notranslate"><span class="pre">comprehension</span></code></a>] <span class="sx">&quot;]&quot;</span>
</pre>
<p>A list display yields a new list object, the contents being specified by either
a list of expressions or a comprehension.  When a comma-separated list of
expressions is supplied, its elements are evaluated from left to right and
placed into the list object in that order.  When a comprehension is supplied,
the list is constructed from the elements resulting from the comprehension.</p>
</section>
<section id="set-displays">
<span id="set"></span><h3><span class="section-number">6.2.7. </span>Set displays<a class="headerlink" href="#set-displays" title="Link to this heading">¶</a></h3>
<p id="index-16">A set display is denoted by curly braces and distinguishable from dictionary
displays by the lack of colons separating keys and values:</p>
<pre class="highlight">
<strong id="grammar-token-python-grammar-set_display">set_display</strong>: <span class="sx">&quot;{&quot;</span> (<a class="reference internal" href="#grammar-token-python-grammar-flexible_expression_list"><code class="xref docutils literal notranslate"><span class="pre">flexible_expression_list</span></code></a> | <a class="reference internal" href="#grammar-token-python-grammar-comprehension"><code class="xref docutils literal notranslate"><span class="pre">comprehension</span></code></a>) <span class="sx">&quot;}&quot;</span>
</pre>
<p>A set display yields a new mutable set object, the contents being specified by
either a sequence of expressions or a comprehension.  When a comma-separated
list of expressions is supplied, its elements are evaluated from left to right
and added to the set object.  When a comprehension is supplied, the set is
constructed from the elements resulting from the comprehension.</p>
<p>An empty set cannot be constructed with <code class="docutils literal notranslate"><span class="pre">{}</span></code>; this literal constructs an empty
dictionary.</p>
</section>
<section id="dictionary-displays">
<span id="dict"></span><h3><span class="section-number">6.2.8. </span>Dictionary displays<a class="headerlink" href="#dictionary-displays" title="Link to this heading">¶</a></h3>
<p id="index-17">A dictionary display is a possibly empty series of dict items (key/value pairs)
enclosed in curly braces:</p>
<pre class="highlight">
<strong id="grammar-token-python-grammar-dict_display">dict_display</strong>:       <span class="sx">&quot;{&quot;</span> [<a class="reference internal" href="#grammar-token-python-grammar-dict_item_list"><code class="xref docutils literal notranslate"><span class="pre">dict_item_list</span></code></a> | <a class="reference internal" href="#grammar-token-python-grammar-dict_comprehension"><code class="xref docutils literal notranslate"><span class="pre">dict_comprehension</span></code></a>] <span class="sx">&quot;}&quot;</span>
<strong id="grammar-token-python-grammar-dict_item_list">dict_item_list</strong>:     <a class="reference internal" href="#grammar-token-python-grammar-dict_item"><code class="xref docutils literal notranslate"><span class="pre">dict_item</span></code></a> (<span class="sx">&quot;,&quot;</span> <a class="reference internal" href="#grammar-token-python-grammar-dict_item"><code class="xref docutils literal notranslate"><span class="pre">dict_item</span></code></a>)* [<span class="sx">&quot;,&quot;</span>]
<strong id="grammar-token-python-grammar-dict_item">dict_item</strong>:          <a class="reference internal" href="#grammar-token-python-grammar-expression"><code class="xref docutils literal notranslate"><span class="pre">expression</span></code></a> <span class="sx">&quot;:&quot;</span> <a class="reference internal" href="#grammar-token-python-grammar-expression"><code class="xref docutils literal notranslate"><span class="pre">expression</span></code></a> | <span class="sx">&quot;**&quot;</span> <a class="reference internal" href="#grammar-token-python-grammar-or_expr"><code class="xref docutils literal notranslate"><span class="pre">or_expr</span></code></a>
<strong id="grammar-token-python-grammar-dict_comprehension">dict_comprehension</strong>: <a class="reference internal" href="#grammar-token-python-grammar-expression"><code class="xref docutils literal notranslate"><span class="pre">expression</span></code></a> <span class="sx">&quot;:&quot;</span> <a class="reference internal" href="#grammar-token-python-grammar-expression"><code class="xref docutils literal notranslate"><span class="pre">expression</span></code></a> <a class="reference internal" href="#grammar-token-python-grammar-comp_for"><code class="xref docutils literal notranslate"><span class="pre">comp_for</span></code></a>
</pre>
<p>A dictionary display yields a new dictionary object.</p>
<p>If a comma-separated sequence of dict items is given, they are evaluated
from left to right to define the entries of the dictionary: each key object is
used as a key into the dictionary to store the corresponding value.  This means
that you can specify the same key multiple times in the dict item list, and the
final dictionary’s value for that key will be the last one given.</p>
<p id="index-18">A double asterisk <code class="docutils literal notranslate"><span class="pre">**</span></code> denotes <em class="dfn">dictionary unpacking</em>.
Its operand must be a <a class="reference internal" href="../glossary.html#term-mapping"><span class="xref std std-term">mapping</span></a>.  Each mapping item is added
to the new dictionary.  Later values replace values already set by
earlier dict items and earlier dictionary unpackings.</p>
<div class="versionadded">
<p><span class="versionmodified added">Added in version 3.5: </span>Unpacking into dictionary displays, originally proposed by <span class="target" id="index-19"></span><a class="pep reference external" href="https://peps.python.org/pep-0448/"><strong>PEP 448</strong></a>.</p>
</div>
<p>A dict comprehension, in contrast to list and set comprehensions, needs two
expressions separated with a colon followed by the usual “for” and “if” clauses.
When the comprehension is run, the resulting key and value elements are inserted
in the new dictionary in the order they are produced.</p>
<p id="index-20">Restrictions on the types of the key values are listed earlier in section
<a class="reference internal" href="datamodel.html#types"><span class="std std-ref">The standard type hierarchy</span></a>.  (To summarize, the key type should be <a class="reference internal" href="../glossary.html#term-hashable"><span class="xref std std-term">hashable</span></a>, which excludes
all mutable objects.)  Clashes between duplicate keys are not detected; the last
value (textually rightmost in the display) stored for a given key value
prevails.</p>
<div class="versionchanged">
<p><span class="versionmodified changed">Changed in version 3.8: </span>Prior to Python 3.8, in dict comprehensions, the evaluation order of key
and value was not well-defined.  In CPython, the value was evaluated before
the key.  Starting with 3.8, the key is evaluated before the value, as
proposed by <span class="target" id="index-21"></span><a class="pep reference external" href="https://peps.python.org/pep-0572/"><strong>PEP 572</strong></a>.</p>
</div>
</section>
<section id="generator-expressions">
<span id="genexpr"></span><h3><span class="section-number">6.2.9. </span>Generator expressions<a class="headerlink" href="#generator-expressions" title="Link to this heading">¶</a></h3>
<p id="index-22">A generator expression is a compact generator notation in parentheses:</p>
<pre class="highlight">
<strong id="grammar-token-python-grammar-generator_expression">generator_expression</strong>: <span class="sx">&quot;(&quot;</span> <a class="reference internal" href="#grammar-token-python-grammar-expression"><code class="xref docutils literal notranslate"><span class="pre">expression</span></code></a> <a class="reference internal" href="#grammar-token-python-grammar-comp_for"><code class="xref docutils literal notranslate"><span class="pre">comp_for</span></code></a> <span class="sx">&quot;)&quot;</span>
</pre>
<p>A generator expression yields a new generator object.  Its syntax is the same as
for comprehensions, except that it is enclosed in parentheses instead of
brackets or curly braces.</p>
<p>Variables used in the generator expression are evaluated lazily when the
<a class="reference internal" href="#generator.__next__" title="generator.__next__"><code class="xref py py-meth docutils literal notranslate"><span class="pre">__next__()</span></code></a> method is called for the generator object (in the same
fashion as normal generators).  However, the iterable expression in the
leftmost <code class="xref std std-keyword docutils literal notranslate"><span class="pre">for</span></code> clause is immediately evaluated, and the
<a class="reference internal" href="../glossary.html#term-iterator"><span class="xref std std-term">iterator</span></a> is immediately created for that iterable, so that an error
produced while creating the iterator will be emitted at the point where the generator expression
is defined, rather than at the point where the first value is retrieved.
Subsequent <code class="xref std std-keyword docutils literal notranslate"><span class="pre">for</span></code> clauses and any filter condition in the leftmost
<code class="xref std std-keyword docutils literal notranslate"><span class="pre">for</span></code> clause cannot be evaluated in the enclosing scope as they may
depend on the values obtained from the leftmost iterable. For example:
<code class="docutils literal notranslate"><span class="pre">(x*y</span> <span class="pre">for</span> <span class="pre">x</span> <span class="pre">in</span> <span class="pre">range(10)</span> <span class="pre">for</span> <span class="pre">y</span> <span class="pre">in</span> <span class="pre">range(x,</span> <span class="pre">x+10))</span></code>.</p>
<p>The parentheses can be omitted on calls with only one argument.  See section
<a class="reference internal" href="#calls"><span class="std std-ref">Calls</span></a> for details.</p>
<p>To avoid interfering with the expected operation of the generator expression
itself, <code class="docutils literal notranslate"><span class="pre">yield</span></code> and <code class="docutils literal notranslate"><span class="pre">yield</span> <span class="pre">from</span></code> expressions are prohibited in the
implicitly defined generator.</p>
<p>If a generator expression contains either <code class="xref std std-keyword docutils literal notranslate"><span class="pre">async</span> <span class="pre">for</span></code>
clauses or <a class="reference internal" href="#await"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">await</span></code></a> expressions it is called an
<em class="dfn">asynchronous generator expression</em>.  An asynchronous generator
expression returns a new asynchronous generator object,
which is an asynchronous iterator (see <a class="reference internal" href="datamodel.html#async-iterators"><span class="std std-ref">Asynchronous Iterators</span></a>).</p>
<div class="versionadded">
<p><span class="versionmodified added">Added in version 3.6: </span>Asynchronous generator expressions were introduced.</p>
</div>
<div class="versionchanged">
<p><span class="versionmodified changed">Changed in version 3.7: </span>Prior to Python 3.7, asynchronous generator expressions could
only appear in <a class="reference internal" href="compound_stmts.html#async-def"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">async</span> <span class="pre">def</span></code></a> coroutines.  Starting
with 3.7, any function can use asynchronous generator expressions.</p>
</div>
<div class="versionchanged">
<p><span class="versionmodified changed">Changed in version 3.8: </span><code class="docutils literal notranslate"><span class="pre">yield</span></code> and <code class="docutils literal notranslate"><span class="pre">yield</span> <span class="pre">from</span></code> prohibited in the implicitly nested scope.</p>
</div>
</section>
<section id="yield-expressions">
<span id="yieldexpr"></span><h3><span class="section-number">6.2.10. </span>Yield expressions<a class="headerlink" href="#yield-expressions" title="Link to this heading">¶</a></h3>
<pre class="highlight" id="index-23">
<strong id="grammar-token-python-grammar-yield_atom">yield_atom</strong>:       <span class="sx">&quot;(&quot;</span> <a class="reference internal" href="#grammar-token-python-grammar-yield_expression"><code class="xref docutils literal notranslate"><span class="pre">yield_expression</span></code></a> <span class="sx">&quot;)&quot;</span>
<strong id="grammar-token-python-grammar-yield_from">yield_from</strong>:       <span class="sx">&quot;yield&quot;</span> <span class="sx">&quot;from&quot;</span> <a class="reference internal" href="#grammar-token-python-grammar-expression"><code class="xref docutils literal notranslate"><span class="pre">expression</span></code></a>
<strong id="grammar-token-python-grammar-yield_expression">yield_expression</strong>: <span class="sx">&quot;yield&quot;</span> <a class="reference internal" href="#grammar-token-python-grammar-yield_list"><code class="xref docutils literal notranslate"><span class="pre">yield_list</span></code></a> | <a class="reference internal" href="#grammar-token-python-grammar-yield_from"><code class="xref docutils literal notranslate"><span class="pre">yield_from</span></code></a>
</pre>
<p>The yield expression is used when defining a <a class="reference internal" href="../glossary.html#term-generator"><span class="xref std std-term">generator</span></a> function
or an <a class="reference internal" href="../glossary.html#term-asynchronous-generator"><span class="xref std std-term">asynchronous generator</span></a> function and
thus can only be used in the body of a function definition.  Using a yield
expression in a function’s body causes that function to be a generator function,
and using it in an <a class="reference internal" href="compound_stmts.html#async-def"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">async</span> <span class="pre">def</span></code></a> function’s body causes that
coroutine function to be an asynchronous generator function. For example:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="k">def</span><span class="w"> </span><span class="nf">gen</span><span class="p">():</span>  <span class="c1"># defines a generator function</span>
    <span class="k">yield</span> <span class="mi">123</span>

<span class="k">async</span> <span class="k">def</span><span class="w"> </span><span class="nf">agen</span><span class="p">():</span> <span class="c1"># defines an asynchronous generator function</span>
    <span class="k">yield</span> <span class="mi">123</span>
</pre></div>
</div>
<p>Due to their side effects on the containing scope, <code class="docutils literal notranslate"><span class="pre">yield</span></code> expressions
are not permitted as part of the implicitly defined scopes used to
implement comprehensions and generator expressions.</p>
<div class="versionchanged">
<p><span class="versionmodified changed">Changed in version 3.8: </span>Yield expressions prohibited in the implicitly nested scopes used to
implement comprehensions and generator expressions.</p>
</div>
<p>Generator functions are described below, while asynchronous generator
functions are described separately in section
<a class="reference internal" href="#asynchronous-generator-functions"><span class="std std-ref">Asynchronous generator functions</span></a>.</p>
<p>When a generator function is called, it returns an iterator known as a
generator.  That generator then controls the execution of the generator
function.  The execution starts when one of the generator’s methods is called.
At that time, the execution proceeds to the first yield expression, where it is
suspended again, returning the value of <a class="reference internal" href="#grammar-token-python-grammar-yield_list"><code class="xref std std-token docutils literal notranslate"><span class="pre">yield_list</span></code></a>
to the generator’s caller,
or <code class="docutils literal notranslate"><span class="pre">None</span></code> if <code class="xref std std-token docutils literal notranslate"><span class="pre">yield_list</span></code> is omitted.
By suspended, we mean that all local state is
retained, including the current bindings of local variables, the instruction
pointer, the internal evaluation stack, and the state of any exception handling.
When the execution is resumed by calling one of the generator’s methods, the
function can proceed exactly as if the yield expression were just another
external call.  The value of the yield expression after resuming depends on the
method which resumed the execution.  If <a class="reference internal" href="#generator.__next__" title="generator.__next__"><code class="xref py py-meth docutils literal notranslate"><span class="pre">__next__()</span></code></a> is used
(typically via either a <a class="reference internal" href="compound_stmts.html#for"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">for</span></code></a> or the <a class="reference internal" href="../library/functions.html#next" title="next"><code class="xref py py-func docutils literal notranslate"><span class="pre">next()</span></code></a> builtin) then the
result is <a class="reference internal" href="../library/constants.html#None" title="None"><code class="xref py py-const docutils literal notranslate"><span class="pre">None</span></code></a>.  Otherwise, if <a class="reference internal" href="#generator.send" title="generator.send"><code class="xref py py-meth docutils literal notranslate"><span class="pre">send()</span></code></a> is used, then
the result will be the value passed in to that method.</p>
<p id="index-24">All of this makes generator functions quite similar to coroutines; they yield
multiple times, they have more than one entry point and their execution can be
suspended.  The only difference is that a generator function cannot control
where the execution should continue after it yields; the control is always
transferred to the generator’s caller.</p>
<p>Yield expressions are allowed anywhere in a <a class="reference internal" href="compound_stmts.html#try"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">try</span></code></a> construct.  If the
generator is not resumed before it is
finalized (by reaching a zero reference count or by being garbage collected),
the generator-iterator’s <a class="reference internal" href="#generator.close" title="generator.close"><code class="xref py py-meth docutils literal notranslate"><span class="pre">close()</span></code></a> method will be called,
allowing any pending <a class="reference internal" href="compound_stmts.html#finally"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">finally</span></code></a> clauses to execute.</p>
<p id="index-25">When <code class="docutils literal notranslate"><span class="pre">yield</span> <span class="pre">from</span> <span class="pre">&lt;expr&gt;</span></code> is used, the supplied expression must be an
iterable. The values produced by iterating that iterable are passed directly
to the caller of the current generator’s methods. Any values passed in with
<a class="reference internal" href="#generator.send" title="generator.send"><code class="xref py py-meth docutils literal notranslate"><span class="pre">send()</span></code></a> and any exceptions passed in with
<a class="reference internal" href="#generator.throw" title="generator.throw"><code class="xref py py-meth docutils literal notranslate"><span class="pre">throw()</span></code></a> are passed to the underlying iterator if it has the
appropriate methods.  If this is not the case, then <code class="xref py py-meth docutils literal notranslate"><span class="pre">send()</span></code>
will raise <a class="reference internal" href="../library/exceptions.html#AttributeError" title="AttributeError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">AttributeError</span></code></a> or <a class="reference internal" href="../library/exceptions.html#TypeError" title="TypeError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">TypeError</span></code></a>, while
<code class="xref py py-meth docutils literal notranslate"><span class="pre">throw()</span></code> will just raise the passed in exception immediately.</p>
<p>When the underlying iterator is complete, the <a class="reference internal" href="../library/exceptions.html#StopIteration.value" title="StopIteration.value"><code class="xref py py-attr docutils literal notranslate"><span class="pre">value</span></code></a>
attribute of the raised <a class="reference internal" href="../library/exceptions.html#StopIteration" title="StopIteration"><code class="xref py py-exc docutils literal notranslate"><span class="pre">StopIteration</span></code></a> instance becomes the value of
the yield expression. It can be either set explicitly when raising
<code class="xref py py-exc docutils literal notranslate"><span class="pre">StopIteration</span></code>, or automatically when the subiterator is a generator
(by returning a value from the subgenerator).</p>
<div class="versionchanged">
<p><span class="versionmodified changed">Changed in version 3.3: </span>Added <code class="docutils literal notranslate"><span class="pre">yield</span> <span class="pre">from</span> <span class="pre">&lt;expr&gt;</span></code> to delegate control flow to a subiterator.</p>
</div>
<p>The parentheses may be omitted when the yield expression is the sole expression
on the right hand side of an assignment statement.</p>
<div class="admonition seealso">
<p class="admonition-title">See also</p>
<dl class="simple">
<dt><span class="target" id="index-26"></span><a class="pep reference external" href="https://peps.python.org/pep-0255/"><strong>PEP 255</strong></a> - Simple Generators</dt><dd><p>The proposal for adding generators and the <a class="reference internal" href="simple_stmts.html#yield"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">yield</span></code></a> statement to Python.</p>
</dd>
<dt><span class="target" id="index-27"></span><a class="pep reference external" href="https://peps.python.org/pep-0342/"><strong>PEP 342</strong></a> - Coroutines via Enhanced Generators</dt><dd><p>The proposal to enhance the API and syntax of generators, making them
usable as simple coroutines.</p>
</dd>
<dt><span class="target" id="index-28"></span><a class="pep reference external" href="https://peps.python.org/pep-0380/"><strong>PEP 380</strong></a> - Syntax for Delegating to a Subgenerator</dt><dd><p>The proposal to introduce the <a class="reference internal" href="#grammar-token-python-grammar-yield_from"><code class="xref std std-token docutils literal notranslate"><span class="pre">yield_from</span></code></a> syntax,
making delegation to subgenerators easy.</p>
</dd>
<dt><span class="target" id="index-29"></span><a class="pep reference external" href="https://peps.python.org/pep-0525/"><strong>PEP 525</strong></a> - Asynchronous Generators</dt><dd><p>The proposal that expanded on <span class="target" id="index-30"></span><a class="pep reference external" href="https://peps.python.org/pep-0492/"><strong>PEP 492</strong></a> by adding generator capabilities to
coroutine functions.</p>
</dd>
</dl>
</div>
<section id="generator-iterator-methods">
<span id="generator-methods"></span><span id="index-31"></span><h4><span class="section-number">6.2.10.1. </span>Generator-iterator methods<a class="headerlink" href="#generator-iterator-methods" title="Link to this heading">¶</a></h4>
<p>This subsection describes the methods of a generator iterator.  They can
be used to control the execution of a generator function.</p>
<p>Note that calling any of the generator methods below when the generator
is already executing raises a <a class="reference internal" href="../library/exceptions.html#ValueError" title="ValueError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">ValueError</span></code></a> exception.</p>
<dl class="py method" id="index-32">
<dt class="sig sig-object py" id="generator.__next__">
<span class="sig-prename descclassname"><span class="pre">generator.</span></span><span class="sig-name descname"><span class="pre">__next__</span></span><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#generator.__next__" title="Link to this definition">¶</a></dt>
<dd><p>Starts the execution of a generator function or resumes it at the last
executed yield expression.  When a generator function is resumed with a
<code class="xref py py-meth docutils literal notranslate"><span class="pre">__next__()</span></code> method, the current yield expression always
evaluates to <a class="reference internal" href="../library/constants.html#None" title="None"><code class="xref py py-const docutils literal notranslate"><span class="pre">None</span></code></a>.  The execution then continues to the next yield
expression, where the generator is suspended again, and the value of the
<a class="reference internal" href="#grammar-token-python-grammar-yield_list"><code class="xref std std-token docutils literal notranslate"><span class="pre">yield_list</span></code></a> is returned to <code class="xref py py-meth docutils literal notranslate"><span class="pre">__next__()</span></code>’s
caller.  If the generator exits without yielding another value, a
<a class="reference internal" href="../library/exceptions.html#StopIteration" title="StopIteration"><code class="xref py py-exc docutils literal notranslate"><span class="pre">StopIteration</span></code></a> exception is raised.</p>
<p>This method is normally called implicitly, e.g. by a <a class="reference internal" href="compound_stmts.html#for"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">for</span></code></a> loop, or
by the built-in <a class="reference internal" href="../library/functions.html#next" title="next"><code class="xref py py-func docutils literal notranslate"><span class="pre">next()</span></code></a> function.</p>
</dd></dl>

<dl class="py method">
<dt class="sig sig-object py" id="generator.send">
<span class="sig-prename descclassname"><span class="pre">generator.</span></span><span class="sig-name descname"><span class="pre">send</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">value</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#generator.send" title="Link to this definition">¶</a></dt>
<dd><p>Resumes the execution and “sends” a value into the generator function.  The
<em>value</em> argument becomes the result of the current yield expression.  The
<code class="xref py py-meth docutils literal notranslate"><span class="pre">send()</span></code> method returns the next value yielded by the generator, or
raises <a class="reference internal" href="../library/exceptions.html#StopIteration" title="StopIteration"><code class="xref py py-exc docutils literal notranslate"><span class="pre">StopIteration</span></code></a> if the generator exits without yielding another
value.  When <code class="xref py py-meth docutils literal notranslate"><span class="pre">send()</span></code> is called to start the generator, it must be called
with <a class="reference internal" href="../library/constants.html#None" title="None"><code class="xref py py-const docutils literal notranslate"><span class="pre">None</span></code></a> as the argument, because there is no yield expression that
could receive the value.</p>
</dd></dl>

<dl class="py method">
<dt class="sig sig-object py" id="generator.throw">
<span class="sig-prename descclassname"><span class="pre">generator.</span></span><span class="sig-name descname"><span class="pre">throw</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">value</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#generator.throw" title="Link to this definition">¶</a></dt>
<dt class="sig sig-object py">
<span class="sig-prename descclassname"><span class="pre">generator.</span></span><span class="sig-name descname"><span class="pre">throw</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">type</span></span></em><span class="optional">[</span>, <em class="sig-param"><span class="n"><span class="pre">value</span></span></em><span class="optional">[</span>, <em class="sig-param"><span class="n"><span class="pre">traceback</span></span></em><span class="optional">]</span><span class="optional">]</span><span class="sig-paren">)</span></dt>
<dd><p>Raises an exception at the point where the generator was paused,
and returns the next value yielded by the generator function.  If the generator
exits without yielding another value, a <a class="reference internal" href="../library/exceptions.html#StopIteration" title="StopIteration"><code class="xref py py-exc docutils literal notranslate"><span class="pre">StopIteration</span></code></a> exception is
raised.  If the generator function does not catch the passed-in exception, or
raises a different exception, then that exception propagates to the caller.</p>
<p>In typical use, this is called with a single exception instance similar to the
way the <a class="reference internal" href="simple_stmts.html#raise"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">raise</span></code></a> keyword is used.</p>
<p>For backwards compatibility, however, the second signature is
supported, following a convention from older versions of Python.
The <em>type</em> argument should be an exception class, and <em>value</em>
should be an exception instance. If the <em>value</em> is not provided, the
<em>type</em> constructor is called to get an instance. If <em>traceback</em>
is provided, it is set on the exception, otherwise any existing
<a class="reference internal" href="../library/exceptions.html#BaseException.__traceback__" title="BaseException.__traceback__"><code class="xref py py-attr docutils literal notranslate"><span class="pre">__traceback__</span></code></a> attribute stored in <em>value</em> may
be cleared.</p>
<div class="versionchanged">
<p><span class="versionmodified changed">Changed in version 3.12: </span>The second signature (type[, value[, traceback]]) is deprecated and
may be removed in a future version of Python.</p>
</div>
</dd></dl>

<dl class="py method" id="index-33">
<dt class="sig sig-object py" id="generator.close">
<span class="sig-prename descclassname"><span class="pre">generator.</span></span><span class="sig-name descname"><span class="pre">close</span></span><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#generator.close" title="Link to this definition">¶</a></dt>
<dd><p>Raises a <a class="reference internal" href="../library/exceptions.html#GeneratorExit" title="GeneratorExit"><code class="xref py py-exc docutils literal notranslate"><span class="pre">GeneratorExit</span></code></a> exception at the point where the generator
function was paused (equivalent to calling <code class="docutils literal notranslate"><span class="pre">throw(GeneratorExit)</span></code>).
The exception is raised by the yield expression where the generator was paused.
If the generator function catches the exception and returns a
value, this value is returned from <code class="xref py py-meth docutils literal notranslate"><span class="pre">close()</span></code>.  If the generator function
is already closed, or raises <code class="xref py py-exc docutils literal notranslate"><span class="pre">GeneratorExit</span></code> (by not catching the
exception), <code class="xref py py-meth docutils literal notranslate"><span class="pre">close()</span></code> returns <a class="reference internal" href="../library/constants.html#None" title="None"><code class="xref py py-const docutils literal notranslate"><span class="pre">None</span></code></a>.  If the generator yields a
value, a <a class="reference internal" href="../library/exceptions.html#RuntimeError" title="RuntimeError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">RuntimeError</span></code></a> is raised.  If the generator raises any other
exception, it is propagated to the caller.  If the generator has already
exited due to an exception or normal exit, <code class="xref py py-meth docutils literal notranslate"><span class="pre">close()</span></code> returns
<code class="xref py py-const docutils literal notranslate"><span class="pre">None</span></code> and has no other effect.</p>
<div class="versionchanged">
<p><span class="versionmodified changed">Changed in version 3.13: </span>If a generator returns a value upon being closed, the value is returned
by <code class="xref py py-meth docutils literal notranslate"><span class="pre">close()</span></code>.</p>
</div>
</dd></dl>

</section>
<section id="examples">
<span id="index-34"></span><h4><span class="section-number">6.2.10.2. </span>Examples<a class="headerlink" href="#examples" title="Link to this heading">¶</a></h4>
<p>Here is a simple example that demonstrates the behavior of generators and
generator functions:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="k">def</span><span class="w"> </span><span class="nf">echo</span><span class="p">(</span><span class="n">value</span><span class="o">=</span><span class="kc">None</span><span class="p">):</span>
<span class="gp">... </span>    <span class="nb">print</span><span class="p">(</span><span class="s2">&quot;Execution starts when &#39;next()&#39; is called for the first time.&quot;</span><span class="p">)</span>
<span class="gp">... </span>    <span class="k">try</span><span class="p">:</span>
<span class="gp">... </span>        <span class="k">while</span> <span class="kc">True</span><span class="p">:</span>
<span class="gp">... </span>            <span class="k">try</span><span class="p">:</span>
<span class="gp">... </span>                <span class="n">value</span> <span class="o">=</span> <span class="p">(</span><span class="k">yield</span> <span class="n">value</span><span class="p">)</span>
<span class="gp">... </span>            <span class="k">except</span> <span class="ne">Exception</span> <span class="k">as</span> <span class="n">e</span><span class="p">:</span>
<span class="gp">... </span>                <span class="n">value</span> <span class="o">=</span> <span class="n">e</span>
<span class="gp">... </span>    <span class="k">finally</span><span class="p">:</span>
<span class="gp">... </span>        <span class="nb">print</span><span class="p">(</span><span class="s2">&quot;Don&#39;t forget to clean up when &#39;close()&#39; is called.&quot;</span><span class="p">)</span>
<span class="gp">...</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">generator</span> <span class="o">=</span> <span class="n">echo</span><span class="p">(</span><span class="mi">1</span><span class="p">)</span>
<span class="gp">&gt;&gt;&gt; </span><span class="nb">print</span><span class="p">(</span><span class="nb">next</span><span class="p">(</span><span class="n">generator</span><span class="p">))</span>
<span class="go">Execution starts when &#39;next()&#39; is called for the first time.</span>
<span class="go">1</span>
<span class="gp">&gt;&gt;&gt; </span><span class="nb">print</span><span class="p">(</span><span class="nb">next</span><span class="p">(</span><span class="n">generator</span><span class="p">))</span>
<span class="go">None</span>
<span class="gp">&gt;&gt;&gt; </span><span class="nb">print</span><span class="p">(</span><span class="n">generator</span><span class="o">.</span><span class="n">send</span><span class="p">(</span><span class="mi">2</span><span class="p">))</span>
<span class="go">2</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">generator</span><span class="o">.</span><span class="n">throw</span><span class="p">(</span><span class="ne">TypeError</span><span class="p">,</span> <span class="s2">&quot;spam&quot;</span><span class="p">)</span>
<span class="go">TypeError(&#39;spam&#39;,)</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">generator</span><span class="o">.</span><span class="n">close</span><span class="p">()</span>
<span class="go">Don&#39;t forget to clean up when &#39;close()&#39; is called.</span>
</pre></div>
</div>
<p>For examples using <code class="docutils literal notranslate"><span class="pre">yield</span> <span class="pre">from</span></code>, see <a class="reference internal" href="../whatsnew/3.3.html#pep-380"><span class="std std-ref">PEP 380: Syntax for Delegating to a Subgenerator</span></a> in “What’s New in
Python.”</p>
</section>
<section id="asynchronous-generator-functions">
<span id="id4"></span><h4><span class="section-number">6.2.10.3. </span>Asynchronous generator functions<a class="headerlink" href="#asynchronous-generator-functions" title="Link to this heading">¶</a></h4>
<p>The presence of a yield expression in a function or method defined using
<a class="reference internal" href="compound_stmts.html#async-def"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">async</span> <span class="pre">def</span></code></a> further defines the function as an
<a class="reference internal" href="../glossary.html#term-asynchronous-generator"><span class="xref std std-term">asynchronous generator</span></a> function.</p>
<p>When an asynchronous generator function is called, it returns an
asynchronous iterator known as an asynchronous generator object.
That object then controls the execution of the generator function.
An asynchronous generator object is typically used in an
<a class="reference internal" href="compound_stmts.html#async-for"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">async</span> <span class="pre">for</span></code></a> statement in a coroutine function analogously to
how a generator object would be used in a <a class="reference internal" href="compound_stmts.html#for"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">for</span></code></a> statement.</p>
<p>Calling one of the asynchronous generator’s methods returns an <a class="reference internal" href="../glossary.html#term-awaitable"><span class="xref std std-term">awaitable</span></a>
object, and the execution starts when this object is awaited on. At that time,
the execution proceeds to the first yield expression, where it is suspended
again, returning the value of <a class="reference internal" href="#grammar-token-python-grammar-yield_list"><code class="xref std std-token docutils literal notranslate"><span class="pre">yield_list</span></code></a> to the
awaiting coroutine. As with a generator, suspension means that all local state
is retained, including the current bindings of local variables, the instruction
pointer, the internal evaluation stack, and the state of any exception handling.
When the execution is resumed by awaiting on the next object returned by the
asynchronous generator’s methods, the function can proceed exactly as if the
yield expression were just another external call. The value of the yield
expression after resuming depends on the method which resumed the execution.  If
<a class="reference internal" href="#agen.__anext__" title="agen.__anext__"><code class="xref py py-meth docutils literal notranslate"><span class="pre">__anext__()</span></code></a> is used then the result is <a class="reference internal" href="../library/constants.html#None" title="None"><code class="xref py py-const docutils literal notranslate"><span class="pre">None</span></code></a>. Otherwise, if
<a class="reference internal" href="#agen.asend" title="agen.asend"><code class="xref py py-meth docutils literal notranslate"><span class="pre">asend()</span></code></a> is used, then the result will be the value passed in to that
method.</p>
<p>If an asynchronous generator happens to exit early by <a class="reference internal" href="simple_stmts.html#break"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">break</span></code></a>, the caller
task being cancelled, or other exceptions, the generator’s async cleanup code
will run and possibly raise exceptions or access context variables in an
unexpected context–perhaps after the lifetime of tasks it depends, or
during the event loop shutdown when the async-generator garbage collection hook
is called.
To prevent this, the caller must explicitly close the async generator by calling
<a class="reference internal" href="#agen.aclose" title="agen.aclose"><code class="xref py py-meth docutils literal notranslate"><span class="pre">aclose()</span></code></a> method to finalize the generator and ultimately detach it
from the event loop.</p>
<p>In an asynchronous generator function, yield expressions are allowed anywhere
in a <a class="reference internal" href="compound_stmts.html#try"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">try</span></code></a> construct. However, if an asynchronous generator is not
resumed before it is finalized (by reaching a zero reference count or by
being garbage collected), then a yield expression within a <code class="xref std std-keyword docutils literal notranslate"><span class="pre">try</span></code>
construct could result in a failure to execute pending <a class="reference internal" href="compound_stmts.html#finally"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">finally</span></code></a>
clauses.  In this case, it is the responsibility of the event loop or
scheduler running the asynchronous generator to call the asynchronous
generator-iterator’s <a class="reference internal" href="#agen.aclose" title="agen.aclose"><code class="xref py py-meth docutils literal notranslate"><span class="pre">aclose()</span></code></a> method and run the resulting
coroutine object, thus allowing any pending <code class="xref std std-keyword docutils literal notranslate"><span class="pre">finally</span></code> clauses
to execute.</p>
<p>To take care of finalization upon event loop termination, an event loop should
define a <em>finalizer</em> function which takes an asynchronous generator-iterator and
presumably calls <a class="reference internal" href="#agen.aclose" title="agen.aclose"><code class="xref py py-meth docutils literal notranslate"><span class="pre">aclose()</span></code></a> and executes the coroutine.
This  <em>finalizer</em> may be registered by calling <a class="reference internal" href="../library/sys.html#sys.set_asyncgen_hooks" title="sys.set_asyncgen_hooks"><code class="xref py py-func docutils literal notranslate"><span class="pre">sys.set_asyncgen_hooks()</span></code></a>.
When first iterated over, an asynchronous generator-iterator will store the
registered <em>finalizer</em> to be called upon finalization. For a reference example
of a <em>finalizer</em> method see the implementation of
<code class="docutils literal notranslate"><span class="pre">asyncio.Loop.shutdown_asyncgens</span></code> in <a class="extlink-source reference external" href="https://github.com/python/cpython/tree/3.14/Lib/asyncio/base_events.py">Lib/asyncio/base_events.py</a>.</p>
<p>The expression <code class="docutils literal notranslate"><span class="pre">yield</span> <span class="pre">from</span> <span class="pre">&lt;expr&gt;</span></code> is a syntax error when used in an
asynchronous generator function.</p>
</section>
<section id="asynchronous-generator-iterator-methods">
<span id="asynchronous-generator-methods"></span><span id="index-35"></span><h4><span class="section-number">6.2.10.4. </span>Asynchronous generator-iterator methods<a class="headerlink" href="#asynchronous-generator-iterator-methods" title="Link to this heading">¶</a></h4>
<p>This subsection describes the methods of an asynchronous generator iterator,
which are used to control the execution of a generator function.</p>
<dl class="py method" id="index-36">
<dt class="sig sig-object py" id="agen.__anext__">
<em class="property"><span class="k"><span class="pre">async</span></span><span class="w"> </span></em><span class="sig-prename descclassname"><span class="pre">agen.</span></span><span class="sig-name descname"><span class="pre">__anext__</span></span><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#agen.__anext__" title="Link to this definition">¶</a></dt>
<dd><p>Returns an awaitable which when run starts to execute the asynchronous
generator or resumes it at the last executed yield expression.  When an
asynchronous generator function is resumed with an <code class="xref py py-meth docutils literal notranslate"><span class="pre">__anext__()</span></code>
method, the current yield expression always evaluates to <a class="reference internal" href="../library/constants.html#None" title="None"><code class="xref py py-const docutils literal notranslate"><span class="pre">None</span></code></a> in the
returned awaitable, which when run will continue to the next yield
expression. The value of the <a class="reference internal" href="#grammar-token-python-grammar-yield_list"><code class="xref std std-token docutils literal notranslate"><span class="pre">yield_list</span></code></a> of the
yield expression is the value of the <a class="reference internal" href="../library/exceptions.html#StopIteration" title="StopIteration"><code class="xref py py-exc docutils literal notranslate"><span class="pre">StopIteration</span></code></a> exception raised by
the completing coroutine.  If the asynchronous generator exits without
yielding another value, the awaitable instead raises a
<a class="reference internal" href="../library/exceptions.html#StopAsyncIteration" title="StopAsyncIteration"><code class="xref py py-exc docutils literal notranslate"><span class="pre">StopAsyncIteration</span></code></a> exception, signalling that the asynchronous
iteration has completed.</p>
<p>This method is normally called implicitly by a <a class="reference internal" href="compound_stmts.html#async-for"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">async</span> <span class="pre">for</span></code></a> loop.</p>
</dd></dl>

<dl class="py method">
<dt class="sig sig-object py" id="agen.asend">
<em class="property"><span class="k"><span class="pre">async</span></span><span class="w"> </span></em><span class="sig-prename descclassname"><span class="pre">agen.</span></span><span class="sig-name descname"><span class="pre">asend</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">value</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#agen.asend" title="Link to this definition">¶</a></dt>
<dd><p>Returns an awaitable which when run resumes the execution of the
asynchronous generator. As with the <a class="reference internal" href="#generator.send" title="generator.send"><code class="xref py py-meth docutils literal notranslate"><span class="pre">send()</span></code></a> method for a
generator, this “sends” a value into the asynchronous generator function,
and the <em>value</em> argument becomes the result of the current yield expression.
The awaitable returned by the <code class="xref py py-meth docutils literal notranslate"><span class="pre">asend()</span></code> method will return the next
value yielded by the generator as the value of the raised
<a class="reference internal" href="../library/exceptions.html#StopIteration" title="StopIteration"><code class="xref py py-exc docutils literal notranslate"><span class="pre">StopIteration</span></code></a>, or raises <a class="reference internal" href="../library/exceptions.html#StopAsyncIteration" title="StopAsyncIteration"><code class="xref py py-exc docutils literal notranslate"><span class="pre">StopAsyncIteration</span></code></a> if the
asynchronous generator exits without yielding another value.  When
<code class="xref py py-meth docutils literal notranslate"><span class="pre">asend()</span></code> is called to start the asynchronous
generator, it must be called with <a class="reference internal" href="../library/constants.html#None" title="None"><code class="xref py py-const docutils literal notranslate"><span class="pre">None</span></code></a> as the argument,
because there is no yield expression that could receive the value.</p>
</dd></dl>

<dl class="py method">
<dt class="sig sig-object py" id="agen.athrow">
<em class="property"><span class="k"><span class="pre">async</span></span><span class="w"> </span></em><span class="sig-prename descclassname"><span class="pre">agen.</span></span><span class="sig-name descname"><span class="pre">athrow</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">value</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#agen.athrow" title="Link to this definition">¶</a></dt>
<dt class="sig sig-object py">
<em class="property"><span class="k"><span class="pre">async</span></span><span class="w"> </span></em><span class="sig-prename descclassname"><span class="pre">agen.</span></span><span class="sig-name descname"><span class="pre">athrow</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">type</span></span></em><span class="optional">[</span>, <em class="sig-param"><span class="n"><span class="pre">value</span></span></em><span class="optional">[</span>, <em class="sig-param"><span class="n"><span class="pre">traceback</span></span></em><span class="optional">]</span><span class="optional">]</span><span class="sig-paren">)</span></dt>
<dd><p>Returns an awaitable that raises an exception of type <code class="docutils literal notranslate"><span class="pre">type</span></code> at the point
where the asynchronous generator was paused, and returns the next value
yielded by the generator function as the value of the raised
<a class="reference internal" href="../library/exceptions.html#StopIteration" title="StopIteration"><code class="xref py py-exc docutils literal notranslate"><span class="pre">StopIteration</span></code></a> exception.  If the asynchronous generator exits
without yielding another value, a <a class="reference internal" href="../library/exceptions.html#StopAsyncIteration" title="StopAsyncIteration"><code class="xref py py-exc docutils literal notranslate"><span class="pre">StopAsyncIteration</span></code></a> exception is
raised by the awaitable.
If the generator function does not catch the passed-in exception, or
raises a different exception, then when the awaitable is run that exception
propagates to the caller of the awaitable.</p>
<div class="versionchanged">
<p><span class="versionmodified changed">Changed in version 3.12: </span>The second signature (type[, value[, traceback]]) is deprecated and
may be removed in a future version of Python.</p>
</div>
</dd></dl>

<dl class="py method" id="index-37">
<dt class="sig sig-object py" id="agen.aclose">
<em class="property"><span class="k"><span class="pre">async</span></span><span class="w"> </span></em><span class="sig-prename descclassname"><span class="pre">agen.</span></span><span class="sig-name descname"><span class="pre">aclose</span></span><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#agen.aclose" title="Link to this definition">¶</a></dt>
<dd><p>Returns an awaitable that when run will throw a <a class="reference internal" href="../library/exceptions.html#GeneratorExit" title="GeneratorExit"><code class="xref py py-exc docutils literal notranslate"><span class="pre">GeneratorExit</span></code></a> into
the asynchronous generator function at the point where it was paused.
If the asynchronous generator function then exits gracefully, is already
closed, or raises <code class="xref py py-exc docutils literal notranslate"><span class="pre">GeneratorExit</span></code> (by not catching the exception),
then the returned awaitable will raise a <a class="reference internal" href="../library/exceptions.html#StopIteration" title="StopIteration"><code class="xref py py-exc docutils literal notranslate"><span class="pre">StopIteration</span></code></a> exception.
Any further awaitables returned by subsequent calls to the asynchronous
generator will raise a <a class="reference internal" href="../library/exceptions.html#StopAsyncIteration" title="StopAsyncIteration"><code class="xref py py-exc docutils literal notranslate"><span class="pre">StopAsyncIteration</span></code></a> exception.  If the
asynchronous generator yields a value, a <a class="reference internal" href="../library/exceptions.html#RuntimeError" title="RuntimeError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">RuntimeError</span></code></a> is raised
by the awaitable.  If the asynchronous generator raises any other exception,
it is propagated to the caller of the awaitable.  If the asynchronous
generator has already exited due to an exception or normal exit, then
further calls to <code class="xref py py-meth docutils literal notranslate"><span class="pre">aclose()</span></code> will return an awaitable that does nothing.</p>
</dd></dl>

</section>
</section>
</section>
<section id="primaries">
<span id="id5"></span><h2><span class="section-number">6.3. </span>Primaries<a class="headerlink" href="#primaries" title="Link to this heading">¶</a></h2>
<p id="index-38">Primaries represent the most tightly bound operations of the language. Their
syntax is:</p>
<pre class="highlight">
<strong id="grammar-token-python-grammar-primary">primary</strong>: <a class="reference internal" href="#grammar-token-python-grammar-atom"><code class="xref docutils literal notranslate"><span class="pre">atom</span></code></a> | <a class="reference internal" href="#grammar-token-python-grammar-attributeref"><code class="xref docutils literal notranslate"><span class="pre">attributeref</span></code></a> | <a class="reference internal" href="#grammar-token-python-grammar-subscription"><code class="xref docutils literal notranslate"><span class="pre">subscription</span></code></a> | <a class="reference internal" href="#grammar-token-python-grammar-call"><code class="xref docutils literal notranslate"><span class="pre">call</span></code></a>
</pre>
<section id="attribute-references">
<span id="id6"></span><h3><span class="section-number">6.3.1. </span>Attribute references<a class="headerlink" href="#attribute-references" title="Link to this heading">¶</a></h3>
<p id="index-39">An attribute reference is a primary followed by a period and a name:</p>
<pre class="highlight">
<strong id="grammar-token-python-grammar-attributeref">attributeref</strong>: <a class="reference internal" href="#grammar-token-python-grammar-primary"><code class="xref docutils literal notranslate"><span class="pre">primary</span></code></a> <span class="sx">&quot;.&quot;</span> <a class="reference internal" href="lexical_analysis.html#grammar-token-python-grammar-identifier"><code class="xref docutils literal notranslate"><span class="pre">identifier</span></code></a>
</pre>
<p id="index-40">The primary must evaluate to an object of a type that supports attribute
references, which most objects do.  This object is then asked to produce the
attribute whose name is the identifier. The type and value produced is
determined by the object.  Multiple evaluations of the same attribute
reference may yield different objects.</p>
<p>This production can be customized by overriding the
<a class="reference internal" href="datamodel.html#object.__getattribute__" title="object.__getattribute__"><code class="xref py py-meth docutils literal notranslate"><span class="pre">__getattribute__()</span></code></a> method or the <a class="reference internal" href="datamodel.html#object.__getattr__" title="object.__getattr__"><code class="xref py py-meth docutils literal notranslate"><span class="pre">__getattr__()</span></code></a>
method.  The <code class="xref py py-meth docutils literal notranslate"><span class="pre">__getattribute__()</span></code> method is called first and either
returns a value or raises <a class="reference internal" href="../library/exceptions.html#AttributeError" title="AttributeError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">AttributeError</span></code></a> if the attribute is not
available.</p>
<p>If an <a class="reference internal" href="../library/exceptions.html#AttributeError" title="AttributeError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">AttributeError</span></code></a> is raised and the object has a <code class="xref py py-meth docutils literal notranslate"><span class="pre">__getattr__()</span></code>
method, that method is called as a fallback.</p>
</section>
<section id="subscriptions-and-slicings">
<span id="subscriptions"></span><h3><span class="section-number">6.3.2. </span>Subscriptions and slicings<a class="headerlink" href="#subscriptions-and-slicings" title="Link to this heading">¶</a></h3>
<p id="index-42"><span id="index-41"></span>The <em class="dfn">subscription</em> syntax is usually used for selecting an element from a
<a class="reference internal" href="datamodel.html#sequence-types"><span class="std std-ref">container</span></a> – for example, to get a value from
a <a class="reference internal" href="../library/stdtypes.html#dict" title="dict"><code class="xref py py-class docutils literal notranslate"><span class="pre">dict</span></code></a>:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="n">digits_by_name</span> <span class="o">=</span> <span class="p">{</span><span class="s1">&#39;one&#39;</span><span class="p">:</span> <span class="mi">1</span><span class="p">,</span> <span class="s1">&#39;two&#39;</span><span class="p">:</span> <span class="mi">2</span><span class="p">}</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">digits_by_name</span><span class="p">[</span><span class="s1">&#39;two&#39;</span><span class="p">]</span>  <span class="c1"># Subscripting a dictionary using the key &#39;two&#39;</span>
<span class="go">2</span>
</pre></div>
</div>
<p>In the subscription syntax, the object being subscribed – a
<a class="reference internal" href="#primaries"><span class="std std-ref">primary</span></a> – is followed by a <em class="dfn">subscript</em> in
square brackets.
In the simplest case, the subscript is a single expression.</p>
<p>Depending on the type of the object being subscribed, the subscript is
sometimes called a <a class="reference internal" href="../glossary.html#term-key"><span class="xref std std-term">key</span></a> (for mappings), <a class="reference internal" href="../glossary.html#term-index"><span class="xref std std-term">index</span></a> (for sequences),
or <em>type argument</em> (for <a class="reference internal" href="../glossary.html#term-generic-type"><span class="xref std std-term">generic types</span></a>).
Syntactically, these are all equivalent:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="n">colors</span> <span class="o">=</span> <span class="p">[</span><span class="s1">&#39;red&#39;</span><span class="p">,</span> <span class="s1">&#39;blue&#39;</span><span class="p">,</span> <span class="s1">&#39;green&#39;</span><span class="p">,</span> <span class="s1">&#39;black&#39;</span><span class="p">]</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">colors</span><span class="p">[</span><span class="mi">3</span><span class="p">]</span>  <span class="c1"># Subscripting a list using the index 3</span>
<span class="go">&#39;black&#39;</span>

<span class="gp">&gt;&gt;&gt; </span><span class="nb">list</span><span class="p">[</span><span class="nb">str</span><span class="p">]</span>  <span class="c1"># Parameterizing the list type using the type argument str</span>
<span class="go">list[str]</span>
</pre></div>
</div>
<p>At runtime, the interpreter will evaluate the primary and
the subscript, and call the primary’s <a class="reference internal" href="datamodel.html#object.__getitem__" title="object.__getitem__"><code class="xref py py-meth docutils literal notranslate"><span class="pre">__getitem__()</span></code></a> or
<a class="reference internal" href="datamodel.html#object.__class_getitem__" title="object.__class_getitem__"><code class="xref py py-meth docutils literal notranslate"><span class="pre">__class_getitem__()</span></code></a> <a class="reference internal" href="../glossary.html#term-special-method"><span class="xref std std-term">special method</span></a> with the subscript
as argument.
For more details on which of these methods is called, see
<a class="reference internal" href="datamodel.html#classgetitem-versus-getitem"><span class="std std-ref">__class_getitem__ versus __getitem__</span></a>.</p>
<p>To show how subscription works, we can define a custom object that
implements <a class="reference internal" href="datamodel.html#object.__getitem__" title="object.__getitem__"><code class="xref py py-meth docutils literal notranslate"><span class="pre">__getitem__()</span></code></a> and prints out the value of
the subscript:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="k">class</span><span class="w"> </span><span class="nc">SubscriptionDemo</span><span class="p">:</span>
<span class="gp">... </span>    <span class="k">def</span><span class="w"> </span><span class="fm">__getitem__</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">key</span><span class="p">):</span>
<span class="gp">... </span>        <span class="nb">print</span><span class="p">(</span><span class="sa">f</span><span class="s1">&#39;subscripted with: </span><span class="si">{</span><span class="n">key</span><span class="si">!r}</span><span class="s1">&#39;</span><span class="p">)</span>
<span class="gp">...</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">demo</span> <span class="o">=</span> <span class="n">SubscriptionDemo</span><span class="p">()</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">demo</span><span class="p">[</span><span class="mi">1</span><span class="p">]</span>
<span class="go">subscripted with: 1</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">demo</span><span class="p">[</span><span class="s1">&#39;a&#39;</span> <span class="o">*</span> <span class="mi">3</span><span class="p">]</span>
<span class="go">subscripted with: &#39;aaa&#39;</span>
</pre></div>
</div>
<p>See <a class="reference internal" href="datamodel.html#object.__getitem__" title="object.__getitem__"><code class="xref py py-meth docutils literal notranslate"><span class="pre">__getitem__()</span></code></a> documentation for how built-in types handle
subscription.</p>
<p>Subscriptions may also be used as targets in <a class="reference internal" href="simple_stmts.html#assignment"><span class="std std-ref">assignment</span></a> or
<a class="reference internal" href="simple_stmts.html#del"><span class="std std-ref">deletion</span></a> statements.
In these cases, the interpreter will call the subscripted object’s
<a class="reference internal" href="datamodel.html#object.__setitem__" title="object.__setitem__"><code class="xref py py-meth docutils literal notranslate"><span class="pre">__setitem__()</span></code></a> or <a class="reference internal" href="datamodel.html#object.__delitem__" title="object.__delitem__"><code class="xref py py-meth docutils literal notranslate"><span class="pre">__delitem__()</span></code></a>
<a class="reference internal" href="../glossary.html#term-special-method"><span class="xref std std-term">special method</span></a>, respectively, instead of <a class="reference internal" href="datamodel.html#object.__getitem__" title="object.__getitem__"><code class="xref py py-meth docutils literal notranslate"><span class="pre">__getitem__()</span></code></a>.</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="n">colors</span> <span class="o">=</span> <span class="p">[</span><span class="s1">&#39;red&#39;</span><span class="p">,</span> <span class="s1">&#39;blue&#39;</span><span class="p">,</span> <span class="s1">&#39;green&#39;</span><span class="p">,</span> <span class="s1">&#39;black&#39;</span><span class="p">]</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">colors</span><span class="p">[</span><span class="mi">3</span><span class="p">]</span> <span class="o">=</span> <span class="s1">&#39;white&#39;</span>  <span class="c1"># Setting item at index</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">colors</span>
<span class="go">[&#39;red&#39;, &#39;blue&#39;, &#39;green&#39;, &#39;white&#39;]</span>
<span class="gp">&gt;&gt;&gt; </span><span class="k">del</span> <span class="n">colors</span><span class="p">[</span><span class="mi">3</span><span class="p">]</span>  <span class="c1"># Deleting item at index 3</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">colors</span>
<span class="go">[&#39;red&#39;, &#39;blue&#39;, &#39;green&#39;]</span>
</pre></div>
</div>
<p>All advanced forms of <em>subscript</em> documented in the following sections
are also usable for assignment and deletion.</p>
<section id="slicings">
<span id="index-44"></span><span id="index-43"></span><span id="id7"></span><h4><span class="section-number">6.3.2.1. </span>Slicings<a class="headerlink" href="#slicings" title="Link to this heading">¶</a></h4>
<p>A more advanced form of subscription, <em class="dfn">slicing</em>, is commonly used
to extract a portion of a <a class="reference internal" href="datamodel.html#datamodel-sequences"><span class="std std-ref">sequence</span></a>.
In this form, the subscript is a <a class="reference internal" href="../glossary.html#term-slice"><span class="xref std std-term">slice</span></a>: up to three
expressions separated by colons.
Any of the expressions may be omitted, but a slice must contain at least one
colon:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="n">number_names</span> <span class="o">=</span> <span class="p">[</span><span class="s1">&#39;zero&#39;</span><span class="p">,</span> <span class="s1">&#39;one&#39;</span><span class="p">,</span> <span class="s1">&#39;two&#39;</span><span class="p">,</span> <span class="s1">&#39;three&#39;</span><span class="p">,</span> <span class="s1">&#39;four&#39;</span><span class="p">,</span> <span class="s1">&#39;five&#39;</span><span class="p">]</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">number_names</span><span class="p">[</span><span class="mi">1</span><span class="p">:</span><span class="mi">3</span><span class="p">]</span>
<span class="go">[&#39;one&#39;, &#39;two&#39;]</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">number_names</span><span class="p">[</span><span class="mi">1</span><span class="p">:]</span>
<span class="go">[&#39;one&#39;, &#39;two&#39;, &#39;three&#39;, &#39;four&#39;, &#39;five&#39;]</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">number_names</span><span class="p">[:</span><span class="mi">3</span><span class="p">]</span>
<span class="go">[&#39;zero&#39;, &#39;one&#39;, &#39;two&#39;]</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">number_names</span><span class="p">[:]</span>
<span class="go">[&#39;zero&#39;, &#39;one&#39;, &#39;two&#39;, &#39;three&#39;, &#39;four&#39;, &#39;five&#39;]</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">number_names</span><span class="p">[::</span><span class="mi">2</span><span class="p">]</span>
<span class="go">[&#39;zero&#39;, &#39;two&#39;, &#39;four&#39;]</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">number_names</span><span class="p">[:</span><span class="o">-</span><span class="mi">3</span><span class="p">]</span>
<span class="go">[&#39;zero&#39;, &#39;one&#39;, &#39;two&#39;]</span>
<span class="gp">&gt;&gt;&gt; </span><span class="k">del</span> <span class="n">number_names</span><span class="p">[</span><span class="mi">4</span><span class="p">:]</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">number_names</span>
<span class="go">[&#39;zero&#39;, &#39;one&#39;, &#39;two&#39;, &#39;three&#39;]</span>
</pre></div>
</div>
<p>When a slice is evaluated, the interpreter constructs a <a class="reference internal" href="../library/functions.html#slice" title="slice"><code class="xref py py-class docutils literal notranslate"><span class="pre">slice</span></code></a> object
whose <a class="reference internal" href="../library/functions.html#slice.start" title="slice.start"><code class="xref py py-attr docutils literal notranslate"><span class="pre">start</span></code></a>, <a class="reference internal" href="../library/functions.html#slice.stop" title="slice.stop"><code class="xref py py-attr docutils literal notranslate"><span class="pre">stop</span></code></a> and
<a class="reference internal" href="../library/functions.html#slice.step" title="slice.step"><code class="xref py py-attr docutils literal notranslate"><span class="pre">step</span></code></a> attributes, respectively, are the results of the
expressions between the colons.
Any missing expression evaluates to <a class="reference internal" href="../library/constants.html#None" title="None"><code class="xref py py-const docutils literal notranslate"><span class="pre">None</span></code></a>.
This <code class="xref py py-class docutils literal notranslate"><span class="pre">slice</span></code> object is then passed to the <a class="reference internal" href="datamodel.html#object.__getitem__" title="object.__getitem__"><code class="xref py py-meth docutils literal notranslate"><span class="pre">__getitem__()</span></code></a>
or <a class="reference internal" href="datamodel.html#object.__class_getitem__" title="object.__class_getitem__"><code class="xref py py-meth docutils literal notranslate"><span class="pre">__class_getitem__()</span></code></a> <a class="reference internal" href="../glossary.html#term-special-method"><span class="xref std std-term">special method</span></a>, as above.</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="c1"># continuing with the SubscriptionDemo instance defined above:</span>
<span class="o">&gt;&gt;&gt;</span> <span class="n">demo</span><span class="p">[</span><span class="mi">2</span><span class="p">:</span><span class="mi">3</span><span class="p">]</span>
<span class="n">subscripted</span> <span class="k">with</span><span class="p">:</span> <span class="nb">slice</span><span class="p">(</span><span class="mi">2</span><span class="p">,</span> <span class="mi">3</span><span class="p">,</span> <span class="kc">None</span><span class="p">)</span>
<span class="o">&gt;&gt;&gt;</span> <span class="n">demo</span><span class="p">[::</span><span class="s1">&#39;spam&#39;</span><span class="p">]</span>
<span class="n">subscripted</span> <span class="k">with</span><span class="p">:</span> <span class="nb">slice</span><span class="p">(</span><span class="kc">None</span><span class="p">,</span> <span class="kc">None</span><span class="p">,</span> <span class="s1">&#39;spam&#39;</span><span class="p">)</span>
</pre></div>
</div>
</section>
<section id="comma-separated-subscripts">
<h4><span class="section-number">6.3.2.2. </span>Comma-separated subscripts<a class="headerlink" href="#comma-separated-subscripts" title="Link to this heading">¶</a></h4>
<p>The subscript can also be given as two or more comma-separated expressions
or slices:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="c1"># continuing with the SubscriptionDemo instance defined above:</span>
<span class="o">&gt;&gt;&gt;</span> <span class="n">demo</span><span class="p">[</span><span class="mi">1</span><span class="p">,</span> <span class="mi">2</span><span class="p">,</span> <span class="mi">3</span><span class="p">]</span>
<span class="n">subscripted</span> <span class="k">with</span><span class="p">:</span> <span class="p">(</span><span class="mi">1</span><span class="p">,</span> <span class="mi">2</span><span class="p">,</span> <span class="mi">3</span><span class="p">)</span>
<span class="o">&gt;&gt;&gt;</span> <span class="n">demo</span><span class="p">[</span><span class="mi">1</span><span class="p">:</span><span class="mi">2</span><span class="p">,</span> <span class="mi">3</span><span class="p">]</span>
<span class="n">subscripted</span> <span class="k">with</span><span class="p">:</span> <span class="p">(</span><span class="nb">slice</span><span class="p">(</span><span class="mi">1</span><span class="p">,</span> <span class="mi">2</span><span class="p">,</span> <span class="kc">None</span><span class="p">),</span> <span class="mi">3</span><span class="p">)</span>
</pre></div>
</div>
<p>This form is commonly used with numerical libraries for slicing
multi-dimensional data.
In this case, the interpreter constructs a <a class="reference internal" href="../library/stdtypes.html#tuple" title="tuple"><code class="xref py py-class docutils literal notranslate"><span class="pre">tuple</span></code></a> of the results of the
expressions or slices, and passes this tuple to the <a class="reference internal" href="datamodel.html#object.__getitem__" title="object.__getitem__"><code class="xref py py-meth docutils literal notranslate"><span class="pre">__getitem__()</span></code></a>
or <a class="reference internal" href="datamodel.html#object.__class_getitem__" title="object.__class_getitem__"><code class="xref py py-meth docutils literal notranslate"><span class="pre">__class_getitem__()</span></code></a> <a class="reference internal" href="../glossary.html#term-special-method"><span class="xref std std-term">special method</span></a>, as above.</p>
<p>The subscript may also be given as a single expression or slice followed
by a comma, to specify a one-element tuple:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="n">demo</span><span class="p">[</span><span class="s1">&#39;spam&#39;</span><span class="p">,]</span>
<span class="go">subscripted with: (&#39;spam&#39;,)</span>
</pre></div>
</div>
</section>
<section id="starred-subscriptions">
<h4><span class="section-number">6.3.2.3. </span>“Starred” subscriptions<a class="headerlink" href="#starred-subscriptions" title="Link to this heading">¶</a></h4>
<div class="versionadded">
<p><span class="versionmodified added">Added in version 3.11: </span>Expressions in <em>tuple_slices</em> may be starred. See <span class="target" id="index-45"></span><a class="pep reference external" href="https://peps.python.org/pep-0646/"><strong>PEP 646</strong></a>.</p>
</div>
<p>The subscript can also contain a starred expression.
In this case, the interpreter unpacks the result into a tuple, and passes
this tuple to <a class="reference internal" href="datamodel.html#object.__getitem__" title="object.__getitem__"><code class="xref py py-meth docutils literal notranslate"><span class="pre">__getitem__()</span></code></a> or <a class="reference internal" href="datamodel.html#object.__class_getitem__" title="object.__class_getitem__"><code class="xref py py-meth docutils literal notranslate"><span class="pre">__class_getitem__()</span></code></a>:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="c1"># continuing with the SubscriptionDemo instance defined above:</span>
<span class="o">&gt;&gt;&gt;</span> <span class="n">demo</span><span class="p">[</span><span class="o">*</span><span class="nb">range</span><span class="p">(</span><span class="mi">10</span><span class="p">)]</span>
<span class="n">subscripted</span> <span class="k">with</span><span class="p">:</span> <span class="p">(</span><span class="mi">0</span><span class="p">,</span> <span class="mi">1</span><span class="p">,</span> <span class="mi">2</span><span class="p">,</span> <span class="mi">3</span><span class="p">,</span> <span class="mi">4</span><span class="p">,</span> <span class="mi">5</span><span class="p">,</span> <span class="mi">6</span><span class="p">,</span> <span class="mi">7</span><span class="p">,</span> <span class="mi">8</span><span class="p">,</span> <span class="mi">9</span><span class="p">)</span>
</pre></div>
</div>
<p>Starred expressions may be combined with comma-separated expressions
and slices:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="n">demo</span><span class="p">[</span><span class="s1">&#39;a&#39;</span><span class="p">,</span> <span class="s1">&#39;b&#39;</span><span class="p">,</span> <span class="o">*</span><span class="nb">range</span><span class="p">(</span><span class="mi">3</span><span class="p">),</span> <span class="s1">&#39;c&#39;</span><span class="p">]</span>
<span class="go">subscripted with: (&#39;a&#39;, &#39;b&#39;, 0, 1, 2, &#39;c&#39;)</span>
</pre></div>
</div>
</section>
<section id="formal-subscription-grammar">
<h4><span class="section-number">6.3.2.4. </span>Formal subscription grammar<a class="headerlink" href="#formal-subscription-grammar" title="Link to this heading">¶</a></h4>
<pre class="highlight">
<strong id="grammar-token-python-grammar-subscription">subscription</strong>:     <a class="reference internal" href="#grammar-token-python-grammar-primary"><code class="xref docutils literal notranslate"><span class="pre">primary</span></code></a> <span class="sx">'['</span> <a class="reference internal" href="#grammar-token-python-grammar-subscript"><code class="xref docutils literal notranslate"><span class="pre">subscript</span></code></a> <span class="sx">']'</span>
<strong id="grammar-token-python-grammar-subscript">subscript</strong>:        <a class="reference internal" href="#grammar-token-python-grammar-single_subscript"><code class="xref docutils literal notranslate"><span class="pre">single_subscript</span></code></a> | <a class="reference internal" href="#grammar-token-python-grammar-tuple_subscript"><code class="xref docutils literal notranslate"><span class="pre">tuple_subscript</span></code></a>
<strong id="grammar-token-python-grammar-single_subscript">single_subscript</strong>: <a class="reference internal" href="#grammar-token-python-grammar-proper_slice"><code class="xref docutils literal notranslate"><span class="pre">proper_slice</span></code></a> | <a class="reference internal" href="#grammar-token-python-grammar-assignment_expression"><code class="xref docutils literal notranslate"><span class="pre">assignment_expression</span></code></a>
<strong id="grammar-token-python-grammar-proper_slice">proper_slice</strong>:     [<a class="reference internal" href="#grammar-token-python-grammar-expression"><code class="xref docutils literal notranslate"><span class="pre">expression</span></code></a>] <span class="sx">&quot;:&quot;</span> [<a class="reference internal" href="#grammar-token-python-grammar-expression"><code class="xref docutils literal notranslate"><span class="pre">expression</span></code></a>] [ <span class="sx">&quot;:&quot;</span> [<a class="reference internal" href="#grammar-token-python-grammar-expression"><code class="xref docutils literal notranslate"><span class="pre">expression</span></code></a>] ]
<strong id="grammar-token-python-grammar-tuple_subscript">tuple_subscript</strong>:  <span class="sx">','</span>.(<a class="reference internal" href="#grammar-token-python-grammar-single_subscript"><code class="xref docutils literal notranslate"><span class="pre">single_subscript</span></code></a> | <a class="reference internal" href="#grammar-token-python-grammar-starred_expression"><code class="xref docutils literal notranslate"><span class="pre">starred_expression</span></code></a>)+ [<span class="sx">','</span>]
</pre>
<p>Recall that the <code class="docutils literal notranslate"><span class="pre">|</span></code> operator <a class="reference internal" href="introduction.html#notation"><span class="std std-ref">denotes ordered choice</span></a>.
Specifically, in <code class="xref std std-token docutils literal notranslate"><span class="pre">subscript</span></code>, if both alternatives would match, the
first (<code class="xref std std-token docutils literal notranslate"><span class="pre">single_subscript</span></code>) has priority.</p>
</section>
</section>
<section id="calls">
<span id="index-46"></span><span id="id8"></span><h3><span class="section-number">6.3.3. </span>Calls<a class="headerlink" href="#calls" title="Link to this heading">¶</a></h3>
<p>A call calls a callable object (e.g., a <a class="reference internal" href="../glossary.html#term-function"><span class="xref std std-term">function</span></a>) with a possibly empty
series of <a class="reference internal" href="../glossary.html#term-argument"><span class="xref std std-term">arguments</span></a>:</p>
<pre class="highlight">
<strong id="grammar-token-python-grammar-call">call</strong>:                 <a class="reference internal" href="#grammar-token-python-grammar-primary"><code class="xref docutils literal notranslate"><span class="pre">primary</span></code></a> <span class="sx">&quot;(&quot;</span> [<a class="reference internal" href="#grammar-token-python-grammar-argument_list"><code class="xref docutils literal notranslate"><span class="pre">argument_list</span></code></a> [<span class="sx">&quot;,&quot;</span>] | <a class="reference internal" href="#grammar-token-python-grammar-comprehension"><code class="xref docutils literal notranslate"><span class="pre">comprehension</span></code></a>] <span class="sx">&quot;)&quot;</span>
<strong id="grammar-token-python-grammar-argument_list">argument_list</strong>:        <a class="reference internal" href="#grammar-token-python-grammar-positional_arguments"><code class="xref docutils literal notranslate"><span class="pre">positional_arguments</span></code></a> [<span class="sx">&quot;,&quot;</span> <a class="reference internal" href="#grammar-token-python-grammar-starred_and_keywords"><code class="xref docutils literal notranslate"><span class="pre">starred_and_keywords</span></code></a>]
                        [<span class="sx">&quot;,&quot;</span> <a class="reference internal" href="#grammar-token-python-grammar-keywords_arguments"><code class="xref docutils literal notranslate"><span class="pre">keywords_arguments</span></code></a>]
                      | <a class="reference internal" href="#grammar-token-python-grammar-starred_and_keywords"><code class="xref docutils literal notranslate"><span class="pre">starred_and_keywords</span></code></a> [<span class="sx">&quot;,&quot;</span> <a class="reference internal" href="#grammar-token-python-grammar-keywords_arguments"><code class="xref docutils literal notranslate"><span class="pre">keywords_arguments</span></code></a>]
                      | <a class="reference internal" href="#grammar-token-python-grammar-keywords_arguments"><code class="xref docutils literal notranslate"><span class="pre">keywords_arguments</span></code></a>
<strong id="grammar-token-python-grammar-positional_arguments">positional_arguments</strong>: <a class="reference internal" href="#grammar-token-python-grammar-positional_item"><code class="xref docutils literal notranslate"><span class="pre">positional_item</span></code></a> (<span class="sx">&quot;,&quot;</span> <a class="reference internal" href="#grammar-token-python-grammar-positional_item"><code class="xref docutils literal notranslate"><span class="pre">positional_item</span></code></a>)*
<strong id="grammar-token-python-grammar-positional_item">positional_item</strong>:      <a class="reference internal" href="#grammar-token-python-grammar-assignment_expression"><code class="xref docutils literal notranslate"><span class="pre">assignment_expression</span></code></a> | <span class="sx">&quot;*&quot;</span> <a class="reference internal" href="#grammar-token-python-grammar-expression"><code class="xref docutils literal notranslate"><span class="pre">expression</span></code></a>
<strong id="grammar-token-python-grammar-starred_and_keywords">starred_and_keywords</strong>: (<span class="sx">&quot;*&quot;</span> <a class="reference internal" href="#grammar-token-python-grammar-expression"><code class="xref docutils literal notranslate"><span class="pre">expression</span></code></a> | <a class="reference internal" href="#grammar-token-python-grammar-keyword_item"><code class="xref docutils literal notranslate"><span class="pre">keyword_item</span></code></a>)
                      (<span class="sx">&quot;,&quot;</span> <span class="sx">&quot;*&quot;</span> <a class="reference internal" href="#grammar-token-python-grammar-expression"><code class="xref docutils literal notranslate"><span class="pre">expression</span></code></a> | <span class="sx">&quot;,&quot;</span> <a class="reference internal" href="#grammar-token-python-grammar-keyword_item"><code class="xref docutils literal notranslate"><span class="pre">keyword_item</span></code></a>)*
<strong id="grammar-token-python-grammar-keywords_arguments">keywords_arguments</strong>:   (<a class="reference internal" href="#grammar-token-python-grammar-keyword_item"><code class="xref docutils literal notranslate"><span class="pre">keyword_item</span></code></a> | <span class="sx">&quot;**&quot;</span> <a class="reference internal" href="#grammar-token-python-grammar-expression"><code class="xref docutils literal notranslate"><span class="pre">expression</span></code></a>)
                      (<span class="sx">&quot;,&quot;</span> <a class="reference internal" href="#grammar-token-python-grammar-keyword_item"><code class="xref docutils literal notranslate"><span class="pre">keyword_item</span></code></a> | <span class="sx">&quot;,&quot;</span> <span class="sx">&quot;**&quot;</span> <a class="reference internal" href="#grammar-token-python-grammar-expression"><code class="xref docutils literal notranslate"><span class="pre">expression</span></code></a>)*
<strong id="grammar-token-python-grammar-keyword_item">keyword_item</strong>:         <a class="reference internal" href="lexical_analysis.html#grammar-token-python-grammar-identifier"><code class="xref docutils literal notranslate"><span class="pre">identifier</span></code></a> <span class="sx">&quot;=&quot;</span> <a class="reference internal" href="#grammar-token-python-grammar-expression"><code class="xref docutils literal notranslate"><span class="pre">expression</span></code></a>
</pre>
<p>An optional trailing comma may be present after the positional and keyword arguments
but does not affect the semantics.</p>
<p id="index-47">The primary must evaluate to a callable object (user-defined functions, built-in
functions, methods of built-in objects, class objects, methods of class
instances, and all objects having a <a class="reference internal" href="datamodel.html#object.__call__" title="object.__call__"><code class="xref py py-meth docutils literal notranslate"><span class="pre">__call__()</span></code></a> method are callable).  All
argument expressions are evaluated before the call is attempted.  Please refer
to section <a class="reference internal" href="compound_stmts.html#function"><span class="std std-ref">Function definitions</span></a> for the syntax of formal <a class="reference internal" href="../glossary.html#term-parameter"><span class="xref std std-term">parameter</span></a> lists.</p>
<p>If keyword arguments are present, they are first converted to positional
arguments, as follows.  First, a list of unfilled slots is created for the
formal parameters.  If there are N positional arguments, they are placed in the
first N slots.  Next, for each keyword argument, the identifier is used to
determine the corresponding slot (if the identifier is the same as the first
formal parameter name, the first slot is used, and so on).  If the slot is
already filled, a <a class="reference internal" href="../library/exceptions.html#TypeError" title="TypeError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">TypeError</span></code></a> exception is raised. Otherwise, the
argument is placed in the slot, filling it (even if the expression is
<code class="docutils literal notranslate"><span class="pre">None</span></code>, it fills the slot).  When all arguments have been processed, the slots
that are still unfilled are filled with the corresponding default value from the
function definition.  (Default values are calculated, once, when the function is
defined; thus, a mutable object such as a list or dictionary used as default
value will be shared by all calls that don’t specify an argument value for the
corresponding slot; this should usually be avoided.)  If there are any unfilled
slots for which no default value is specified, a <code class="xref py py-exc docutils literal notranslate"><span class="pre">TypeError</span></code> exception is
raised.  Otherwise, the list of filled slots is used as the argument list for
the call.</p>
<div class="impl-detail compound">
<p><strong>CPython implementation detail:</strong> An implementation may provide built-in functions whose positional parameters
do not have names, even if they are ‘named’ for the purpose of documentation,
and which therefore cannot be supplied by keyword.  In CPython, this is the
case for functions implemented in C that use <a class="reference internal" href="../c-api/arg.html#c.PyArg_ParseTuple" title="PyArg_ParseTuple"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyArg_ParseTuple()</span></code></a> to
parse their arguments.</p>
</div>
<p>If there are more positional arguments than there are formal parameter slots, a
<a class="reference internal" href="../library/exceptions.html#TypeError" title="TypeError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">TypeError</span></code></a> exception is raised, unless a formal parameter using the syntax
<code class="docutils literal notranslate"><span class="pre">*identifier</span></code> is present; in this case, that formal parameter receives a tuple
containing the excess positional arguments (or an empty tuple if there were no
excess positional arguments).</p>
<p>If any keyword argument does not correspond to a formal parameter name, a
<a class="reference internal" href="../library/exceptions.html#TypeError" title="TypeError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">TypeError</span></code></a> exception is raised, unless a formal parameter using the syntax
<code class="docutils literal notranslate"><span class="pre">**identifier</span></code> is present; in this case, that formal parameter receives a
dictionary containing the excess keyword arguments (using the keywords as keys
and the argument values as corresponding values), or a (new) empty dictionary if
there were no excess keyword arguments.</p>
<p id="index-48">If the syntax <code class="docutils literal notranslate"><span class="pre">*expression</span></code> appears in the function call, <code class="docutils literal notranslate"><span class="pre">expression</span></code> must
evaluate to an <a class="reference internal" href="../glossary.html#term-iterable"><span class="xref std std-term">iterable</span></a>.  Elements from these iterables are
treated as if they were additional positional arguments.  For the call
<code class="docutils literal notranslate"><span class="pre">f(x1,</span> <span class="pre">x2,</span> <span class="pre">*y,</span> <span class="pre">x3,</span> <span class="pre">x4)</span></code>, if <em>y</em> evaluates to a sequence <em>y1</em>, …, <em>yM</em>,
this is equivalent to a call with M+4 positional arguments <em>x1</em>, <em>x2</em>,
<em>y1</em>, …, <em>yM</em>, <em>x3</em>, <em>x4</em>.</p>
<p>A consequence of this is that although the <code class="docutils literal notranslate"><span class="pre">*expression</span></code> syntax may appear
<em>after</em> explicit keyword arguments, it is processed <em>before</em> the
keyword arguments (and any <code class="docutils literal notranslate"><span class="pre">**expression</span></code> arguments – see below).  So:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="k">def</span><span class="w"> </span><span class="nf">f</span><span class="p">(</span><span class="n">a</span><span class="p">,</span> <span class="n">b</span><span class="p">):</span>
<span class="gp">... </span>    <span class="nb">print</span><span class="p">(</span><span class="n">a</span><span class="p">,</span> <span class="n">b</span><span class="p">)</span>
<span class="gp">...</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">f</span><span class="p">(</span><span class="n">b</span><span class="o">=</span><span class="mi">1</span><span class="p">,</span> <span class="o">*</span><span class="p">(</span><span class="mi">2</span><span class="p">,))</span>
<span class="go">2 1</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">f</span><span class="p">(</span><span class="n">a</span><span class="o">=</span><span class="mi">1</span><span class="p">,</span> <span class="o">*</span><span class="p">(</span><span class="mi">2</span><span class="p">,))</span>
<span class="gt">Traceback (most recent call last):</span>
  File <span class="nb">&quot;&lt;stdin&gt;&quot;</span>, line <span class="m">1</span>, in <span class="n">&lt;module&gt;</span>
<span class="gr">TypeError</span>: <span class="n">f() got multiple values for keyword argument &#39;a&#39;</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">f</span><span class="p">(</span><span class="mi">1</span><span class="p">,</span> <span class="o">*</span><span class="p">(</span><span class="mi">2</span><span class="p">,))</span>
<span class="go">1 2</span>
</pre></div>
</div>
<p>It is unusual for both keyword arguments and the <code class="docutils literal notranslate"><span class="pre">*expression</span></code> syntax to be
used in the same call, so in practice this confusion does not often arise.</p>
<p id="index-49">If the syntax <code class="docutils literal notranslate"><span class="pre">**expression</span></code> appears in the function call, <code class="docutils literal notranslate"><span class="pre">expression</span></code> must
evaluate to a <a class="reference internal" href="../glossary.html#term-mapping"><span class="xref std std-term">mapping</span></a>, the contents of which are treated as
additional keyword arguments. If a parameter matching a key has already been
given a value (by an explicit keyword argument, or from another unpacking),
a <a class="reference internal" href="../library/exceptions.html#TypeError" title="TypeError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">TypeError</span></code></a> exception is raised.</p>
<p>When <code class="docutils literal notranslate"><span class="pre">**expression</span></code> is used, each key in this mapping must be
a string.
Each value from the mapping is assigned to the first formal parameter
eligible for keyword assignment whose name is equal to the key.
A key need not be a Python identifier (e.g. <code class="docutils literal notranslate"><span class="pre">&quot;max-temp</span> <span class="pre">°F&quot;</span></code> is acceptable,
although it will not match any formal parameter that could be declared).
If there is no match to a formal parameter
the key-value pair is collected by the <code class="docutils literal notranslate"><span class="pre">**</span></code> parameter, if there is one,
or if there is not, a <a class="reference internal" href="../library/exceptions.html#TypeError" title="TypeError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">TypeError</span></code></a> exception is raised.</p>
<p>Formal parameters using the syntax <code class="docutils literal notranslate"><span class="pre">*identifier</span></code> or <code class="docutils literal notranslate"><span class="pre">**identifier</span></code> cannot be
used as positional argument slots or as keyword argument names.</p>
<div class="versionchanged">
<p><span class="versionmodified changed">Changed in version 3.5: </span>Function calls accept any number of <code class="docutils literal notranslate"><span class="pre">*</span></code> and <code class="docutils literal notranslate"><span class="pre">**</span></code> unpackings,
positional arguments may follow iterable unpackings (<code class="docutils literal notranslate"><span class="pre">*</span></code>),
and keyword arguments may follow dictionary unpackings (<code class="docutils literal notranslate"><span class="pre">**</span></code>).
Originally proposed by <span class="target" id="index-50"></span><a class="pep reference external" href="https://peps.python.org/pep-0448/"><strong>PEP 448</strong></a>.</p>
</div>
<p>A call always returns some value, possibly <code class="docutils literal notranslate"><span class="pre">None</span></code>, unless it raises an
exception.  How this value is computed depends on the type of the callable
object.</p>
<p>If it is—</p>
<dl>
<dt>a user-defined function:</dt><dd><p id="index-51">The code block for the function is executed, passing it the argument list.  The
first thing the code block will do is bind the formal parameters to the
arguments; this is described in section <a class="reference internal" href="compound_stmts.html#function"><span class="std std-ref">Function definitions</span></a>.  When the code block
executes a <a class="reference internal" href="simple_stmts.html#return"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">return</span></code></a> statement, this specifies the return value of the
function call.  If execution reaches the end of the code block without
executing a <code class="xref std std-keyword docutils literal notranslate"><span class="pre">return</span></code> statement, the return value is <code class="docutils literal notranslate"><span class="pre">None</span></code>.</p>
</dd>
<dt>a built-in function or method:</dt><dd><p id="index-52">The result is up to the interpreter; see <a class="reference internal" href="../library/functions.html#built-in-funcs"><span class="std std-ref">Built-in Functions</span></a> for the
descriptions of built-in functions and methods.</p>
</dd>
<dt>a class object:</dt><dd><p id="index-53">A new instance of that class is returned.</p>
</dd>
<dt>a class instance method:</dt><dd><p id="index-54">The corresponding user-defined function is called, with an argument list that is
one longer than the argument list of the call: the instance becomes the first
argument.</p>
</dd>
<dt>a class instance:</dt><dd><p id="index-55">The class must define a <a class="reference internal" href="datamodel.html#object.__call__" title="object.__call__"><code class="xref py py-meth docutils literal notranslate"><span class="pre">__call__()</span></code></a> method; the effect is then the same as
if that method was called.</p>
</dd>
</dl>
</section>
</section>
<section id="await-expression">
<span id="await"></span><span id="index-56"></span><h2><span class="section-number">6.4. </span>Await expression<a class="headerlink" href="#await-expression" title="Link to this heading">¶</a></h2>
<p>Suspend the execution of <a class="reference internal" href="../glossary.html#term-coroutine"><span class="xref std std-term">coroutine</span></a> on an <a class="reference internal" href="../glossary.html#term-awaitable"><span class="xref std std-term">awaitable</span></a> object.
Can only be used inside a <a class="reference internal" href="../glossary.html#term-coroutine-function"><span class="xref std std-term">coroutine function</span></a>.</p>
<pre class="highlight">
<strong id="grammar-token-python-grammar-await_expr">await_expr</strong>: <span class="sx">&quot;await&quot;</span> <a class="reference internal" href="#grammar-token-python-grammar-primary"><code class="xref docutils literal notranslate"><span class="pre">primary</span></code></a>
</pre>
<div class="versionadded">
<p><span class="versionmodified added">Added in version 3.5.</span></p>
</div>
</section>
<section id="the-power-operator">
<span id="power"></span><h2><span class="section-number">6.5. </span>The power operator<a class="headerlink" href="#the-power-operator" title="Link to this heading">¶</a></h2>
<p id="index-57">The power operator binds more tightly than unary operators on its left; it binds
less tightly than unary operators on its right.  The syntax is:</p>
<pre class="highlight">
<strong id="grammar-token-python-grammar-power">power</strong>: (<a class="reference internal" href="#grammar-token-python-grammar-await_expr"><code class="xref docutils literal notranslate"><span class="pre">await_expr</span></code></a> | <a class="reference internal" href="#grammar-token-python-grammar-primary"><code class="xref docutils literal notranslate"><span class="pre">primary</span></code></a>) [<span class="sx">&quot;**&quot;</span> <a class="reference internal" href="#grammar-token-python-grammar-u_expr"><code class="xref docutils literal notranslate"><span class="pre">u_expr</span></code></a>]
</pre>
<p>Thus, in an unparenthesized sequence of power and unary operators, the operators
are evaluated from right to left (this does not constrain the evaluation order
for the operands): <code class="docutils literal notranslate"><span class="pre">-1**2</span></code> results in <code class="docutils literal notranslate"><span class="pre">-1</span></code>.</p>
<p>The power operator has the same semantics as the built-in <a class="reference internal" href="../library/functions.html#pow" title="pow"><code class="xref py py-func docutils literal notranslate"><span class="pre">pow()</span></code></a> function,
when called with two arguments: it yields its left argument raised to the power
of its right argument.
Numeric arguments are first <a class="reference internal" href="../library/stdtypes.html#stdtypes-mixed-arithmetic"><span class="std std-ref">converted to a common type</span></a>,
and the result is of that type.</p>
<p>For int operands, the result has the same type as the operands unless the second
argument is negative; in that case, all arguments are converted to float and a
float result is delivered. For example, <code class="docutils literal notranslate"><span class="pre">10**2</span></code> returns <code class="docutils literal notranslate"><span class="pre">100</span></code>, but
<code class="docutils literal notranslate"><span class="pre">10**-2</span></code> returns <code class="docutils literal notranslate"><span class="pre">0.01</span></code>.</p>
<p>Raising <code class="docutils literal notranslate"><span class="pre">0.0</span></code> to a negative power results in a <a class="reference internal" href="../library/exceptions.html#ZeroDivisionError" title="ZeroDivisionError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">ZeroDivisionError</span></code></a>.
Raising a negative number to a fractional power results in a <a class="reference internal" href="../library/functions.html#complex" title="complex"><code class="xref py py-class docutils literal notranslate"><span class="pre">complex</span></code></a>
number. (In earlier versions it raised a <a class="reference internal" href="../library/exceptions.html#ValueError" title="ValueError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">ValueError</span></code></a>.)</p>
<p>This operation can be customized using the special <a class="reference internal" href="datamodel.html#object.__pow__" title="object.__pow__"><code class="xref py py-meth docutils literal notranslate"><span class="pre">__pow__()</span></code></a> and
<a class="reference internal" href="datamodel.html#object.__rpow__" title="object.__rpow__"><code class="xref py py-meth docutils literal notranslate"><span class="pre">__rpow__()</span></code></a> methods.</p>
</section>
<section id="unary-arithmetic-and-bitwise-operations">
<span id="unary"></span><h2><span class="section-number">6.6. </span>Unary arithmetic and bitwise operations<a class="headerlink" href="#unary-arithmetic-and-bitwise-operations" title="Link to this heading">¶</a></h2>
<p id="index-58">All unary arithmetic and bitwise operations have the same priority:</p>
<pre class="highlight">
<strong id="grammar-token-python-grammar-u_expr">u_expr</strong>: <a class="reference internal" href="#grammar-token-python-grammar-power"><code class="xref docutils literal notranslate"><span class="pre">power</span></code></a> | <span class="sx">&quot;-&quot;</span> <a class="reference internal" href="#grammar-token-python-grammar-u_expr"><code class="xref docutils literal notranslate"><span class="pre">u_expr</span></code></a> | <span class="sx">&quot;+&quot;</span> <a class="reference internal" href="#grammar-token-python-grammar-u_expr"><code class="xref docutils literal notranslate"><span class="pre">u_expr</span></code></a> | <span class="sx">&quot;~&quot;</span> <a class="reference internal" href="#grammar-token-python-grammar-u_expr"><code class="xref docutils literal notranslate"><span class="pre">u_expr</span></code></a>
</pre>
<p id="index-59">The unary <code class="docutils literal notranslate"><span class="pre">-</span></code> (minus) operator yields the negation of its numeric argument; the
operation can be overridden with the <a class="reference internal" href="datamodel.html#object.__neg__" title="object.__neg__"><code class="xref py py-meth docutils literal notranslate"><span class="pre">__neg__()</span></code></a> special method.</p>
<p id="index-60">The unary <code class="docutils literal notranslate"><span class="pre">+</span></code> (plus) operator yields its numeric argument unchanged; the
operation can be overridden with the <a class="reference internal" href="datamodel.html#object.__pos__" title="object.__pos__"><code class="xref py py-meth docutils literal notranslate"><span class="pre">__pos__()</span></code></a> special method.</p>
<p id="index-61">The unary <code class="docutils literal notranslate"><span class="pre">~</span></code> (invert) operator yields the bitwise inversion of its integer
argument.  The bitwise inversion of <code class="docutils literal notranslate"><span class="pre">x</span></code> is defined as <code class="docutils literal notranslate"><span class="pre">-(x+1)</span></code>.  It only
applies to integral numbers or to custom objects that override the
<a class="reference internal" href="datamodel.html#object.__invert__" title="object.__invert__"><code class="xref py py-meth docutils literal notranslate"><span class="pre">__invert__()</span></code></a> special method.</p>
<p id="index-62">In all three cases, if the argument does not have the proper type, a
<a class="reference internal" href="../library/exceptions.html#TypeError" title="TypeError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">TypeError</span></code></a> exception is raised.</p>
</section>
<section id="binary-arithmetic-operations">
<span id="binary"></span><h2><span class="section-number">6.7. </span>Binary arithmetic operations<a class="headerlink" href="#binary-arithmetic-operations" title="Link to this heading">¶</a></h2>
<p id="index-63">The binary arithmetic operations have the conventional priority levels.  Note
that some of these operations also apply to certain non-numeric types.  Apart
from the power operator, there are only two levels, one for multiplicative
operators and one for additive operators:</p>
<pre class="highlight">
<strong id="grammar-token-python-grammar-m_expr">m_expr</strong>: <a class="reference internal" href="#grammar-token-python-grammar-u_expr"><code class="xref docutils literal notranslate"><span class="pre">u_expr</span></code></a> | <a class="reference internal" href="#grammar-token-python-grammar-m_expr"><code class="xref docutils literal notranslate"><span class="pre">m_expr</span></code></a> <span class="sx">&quot;*&quot;</span> <a class="reference internal" href="#grammar-token-python-grammar-u_expr"><code class="xref docutils literal notranslate"><span class="pre">u_expr</span></code></a> | <a class="reference internal" href="#grammar-token-python-grammar-m_expr"><code class="xref docutils literal notranslate"><span class="pre">m_expr</span></code></a> <span class="sx">&quot;&#64;&quot;</span> <a class="reference internal" href="#grammar-token-python-grammar-m_expr"><code class="xref docutils literal notranslate"><span class="pre">m_expr</span></code></a> |
        <a class="reference internal" href="#grammar-token-python-grammar-m_expr"><code class="xref docutils literal notranslate"><span class="pre">m_expr</span></code></a> <span class="sx">&quot;//&quot;</span> <a class="reference internal" href="#grammar-token-python-grammar-u_expr"><code class="xref docutils literal notranslate"><span class="pre">u_expr</span></code></a> | <a class="reference internal" href="#grammar-token-python-grammar-m_expr"><code class="xref docutils literal notranslate"><span class="pre">m_expr</span></code></a> <span class="sx">&quot;/&quot;</span> <a class="reference internal" href="#grammar-token-python-grammar-u_expr"><code class="xref docutils literal notranslate"><span class="pre">u_expr</span></code></a> |
        <a class="reference internal" href="#grammar-token-python-grammar-m_expr"><code class="xref docutils literal notranslate"><span class="pre">m_expr</span></code></a> <span class="sx">&quot;%&quot;</span> <a class="reference internal" href="#grammar-token-python-grammar-u_expr"><code class="xref docutils literal notranslate"><span class="pre">u_expr</span></code></a>
<strong id="grammar-token-python-grammar-a_expr">a_expr</strong>: <a class="reference internal" href="#grammar-token-python-grammar-m_expr"><code class="xref docutils literal notranslate"><span class="pre">m_expr</span></code></a> | <a class="reference internal" href="#grammar-token-python-grammar-a_expr"><code class="xref docutils literal notranslate"><span class="pre">a_expr</span></code></a> <span class="sx">&quot;+&quot;</span> <a class="reference internal" href="#grammar-token-python-grammar-m_expr"><code class="xref docutils literal notranslate"><span class="pre">m_expr</span></code></a> | <a class="reference internal" href="#grammar-token-python-grammar-a_expr"><code class="xref docutils literal notranslate"><span class="pre">a_expr</span></code></a> <span class="sx">&quot;-&quot;</span> <a class="reference internal" href="#grammar-token-python-grammar-m_expr"><code class="xref docutils literal notranslate"><span class="pre">m_expr</span></code></a>
</pre>
<p id="index-64">The <code class="docutils literal notranslate"><span class="pre">*</span></code> (multiplication) operator yields the product of its arguments.  The
arguments must either both be numbers, or one argument must be an integer and
the other must be a sequence. In the former case, the numbers are
<a class="reference internal" href="../library/stdtypes.html#stdtypes-mixed-arithmetic"><span class="std std-ref">converted to a common real type</span></a> and then
multiplied together.  In the latter case, sequence repetition is performed;
a negative repetition factor yields an empty sequence.</p>
<p>This operation can be customized using the special <a class="reference internal" href="datamodel.html#object.__mul__" title="object.__mul__"><code class="xref py py-meth docutils literal notranslate"><span class="pre">__mul__()</span></code></a> and
<a class="reference internal" href="datamodel.html#object.__rmul__" title="object.__rmul__"><code class="xref py py-meth docutils literal notranslate"><span class="pre">__rmul__()</span></code></a> methods.</p>
<div class="versionchanged">
<p><span class="versionmodified changed">Changed in version 3.14: </span>If only one operand is a complex number, the other operand is converted
to a floating-point number.</p>
</div>
<p id="index-65">The <code class="docutils literal notranslate"><span class="pre">&#64;</span></code> (at) operator is intended to be used for matrix multiplication.  No
builtin Python types implement this operator.</p>
<p>This operation can be customized using the special <a class="reference internal" href="datamodel.html#object.__matmul__" title="object.__matmul__"><code class="xref py py-meth docutils literal notranslate"><span class="pre">__matmul__()</span></code></a> and
<a class="reference internal" href="datamodel.html#object.__rmatmul__" title="object.__rmatmul__"><code class="xref py py-meth docutils literal notranslate"><span class="pre">__rmatmul__()</span></code></a> methods.</p>
<div class="versionadded">
<p><span class="versionmodified added">Added in version 3.5.</span></p>
</div>
<p id="index-66">The <code class="docutils literal notranslate"><span class="pre">/</span></code> (division) and <code class="docutils literal notranslate"><span class="pre">//</span></code> (floor division) operators yield the quotient of
their arguments.  The numeric arguments are first
<a class="reference internal" href="../library/stdtypes.html#stdtypes-mixed-arithmetic"><span class="std std-ref">converted to a common type</span></a>.
Division of integers yields a float, while floor division of integers results in an
integer; the result is that of mathematical division with the ‘floor’ function
applied to the result.  Division by zero raises the <a class="reference internal" href="../library/exceptions.html#ZeroDivisionError" title="ZeroDivisionError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">ZeroDivisionError</span></code></a>
exception.</p>
<p>The division operation can be customized using the special <a class="reference internal" href="datamodel.html#object.__truediv__" title="object.__truediv__"><code class="xref py py-meth docutils literal notranslate"><span class="pre">__truediv__()</span></code></a>
and <a class="reference internal" href="datamodel.html#object.__rtruediv__" title="object.__rtruediv__"><code class="xref py py-meth docutils literal notranslate"><span class="pre">__rtruediv__()</span></code></a> methods.
The floor division operation can be customized using the special
<a class="reference internal" href="datamodel.html#object.__floordiv__" title="object.__floordiv__"><code class="xref py py-meth docutils literal notranslate"><span class="pre">__floordiv__()</span></code></a> and <a class="reference internal" href="datamodel.html#object.__rfloordiv__" title="object.__rfloordiv__"><code class="xref py py-meth docutils literal notranslate"><span class="pre">__rfloordiv__()</span></code></a> methods.</p>
<p id="index-67">The <code class="docutils literal notranslate"><span class="pre">%</span></code> (modulo) operator yields the remainder from the division of the first
argument by the second.  The numeric arguments are first
<a class="reference internal" href="../library/stdtypes.html#stdtypes-mixed-arithmetic"><span class="std std-ref">converted to a common type</span></a>.
A zero right argument raises the <a class="reference internal" href="../library/exceptions.html#ZeroDivisionError" title="ZeroDivisionError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">ZeroDivisionError</span></code></a> exception.  The
arguments may be floating-point numbers, e.g., <code class="docutils literal notranslate"><span class="pre">3.14%0.7</span></code> equals <code class="docutils literal notranslate"><span class="pre">0.34</span></code>
(since <code class="docutils literal notranslate"><span class="pre">3.14</span></code> equals <code class="docutils literal notranslate"><span class="pre">4*0.7</span> <span class="pre">+</span> <span class="pre">0.34</span></code>.)  The modulo operator always yields a
result with the same sign as its second operand (or zero); the absolute value of
the result is strictly smaller than the absolute value of the second operand
<a class="footnote-reference brackets" href="#id18" id="id9" role="doc-noteref"><span class="fn-bracket">[</span>1<span class="fn-bracket">]</span></a>.</p>
<p>The floor division and modulo operators are connected by the following
identity: <code class="docutils literal notranslate"><span class="pre">x</span> <span class="pre">==</span> <span class="pre">(x//y)*y</span> <span class="pre">+</span> <span class="pre">(x%y)</span></code>.  Floor division and modulo are also
connected with the built-in function <a class="reference internal" href="../library/functions.html#divmod" title="divmod"><code class="xref py py-func docutils literal notranslate"><span class="pre">divmod()</span></code></a>: <code class="docutils literal notranslate"><span class="pre">divmod(x,</span> <span class="pre">y)</span> <span class="pre">==</span> <span class="pre">(x//y,</span>
<span class="pre">x%y)</span></code>. <a class="footnote-reference brackets" href="#id19" id="id10" role="doc-noteref"><span class="fn-bracket">[</span>2<span class="fn-bracket">]</span></a>.</p>
<p>In addition to performing the modulo operation on numbers, the <code class="docutils literal notranslate"><span class="pre">%</span></code> operator is
also overloaded by string objects to perform old-style string formatting (also
known as interpolation).  The syntax for string formatting is described in the
Python Library Reference, section <a class="reference internal" href="../library/stdtypes.html#old-string-formatting"><span class="std std-ref">printf-style String Formatting</span></a>.</p>
<p>The <em>modulo</em> operation can be customized using the special <a class="reference internal" href="datamodel.html#object.__mod__" title="object.__mod__"><code class="xref py py-meth docutils literal notranslate"><span class="pre">__mod__()</span></code></a>
and <a class="reference internal" href="datamodel.html#object.__rmod__" title="object.__rmod__"><code class="xref py py-meth docutils literal notranslate"><span class="pre">__rmod__()</span></code></a> methods.</p>
<p>The floor division operator, the modulo operator, and the <a class="reference internal" href="../library/functions.html#divmod" title="divmod"><code class="xref py py-func docutils literal notranslate"><span class="pre">divmod()</span></code></a>
function are not defined for complex numbers.  Instead, convert to a
floating-point number using the <a class="reference internal" href="../library/functions.html#abs" title="abs"><code class="xref py py-func docutils literal notranslate"><span class="pre">abs()</span></code></a> function if appropriate.</p>
<p id="index-68">The <code class="docutils literal notranslate"><span class="pre">+</span></code> (addition) operator yields the sum of its arguments.  The arguments
must either both be numbers or both be sequences of the same type.  In the
former case, the numbers are
<a class="reference internal" href="../library/stdtypes.html#stdtypes-mixed-arithmetic"><span class="std std-ref">converted to a common real type</span></a> and then
added together.
In the latter case, the sequences are concatenated.</p>
<p>This operation can be customized using the special <a class="reference internal" href="datamodel.html#object.__add__" title="object.__add__"><code class="xref py py-meth docutils literal notranslate"><span class="pre">__add__()</span></code></a> and
<a class="reference internal" href="datamodel.html#object.__radd__" title="object.__radd__"><code class="xref py py-meth docutils literal notranslate"><span class="pre">__radd__()</span></code></a> methods.</p>
<div class="versionchanged">
<p><span class="versionmodified changed">Changed in version 3.14: </span>If only one operand is a complex number, the other operand is converted
to a floating-point number.</p>
</div>
<p id="index-69">The <code class="docutils literal notranslate"><span class="pre">-</span></code> (subtraction) operator yields the difference of its arguments.
The numeric arguments are first
<a class="reference internal" href="../library/stdtypes.html#stdtypes-mixed-arithmetic"><span class="std std-ref">converted to a common real type</span></a>.</p>
<p>This operation can be customized using the special <a class="reference internal" href="datamodel.html#object.__sub__" title="object.__sub__"><code class="xref py py-meth docutils literal notranslate"><span class="pre">__sub__()</span></code></a> and
<a class="reference internal" href="datamodel.html#object.__rsub__" title="object.__rsub__"><code class="xref py py-meth docutils literal notranslate"><span class="pre">__rsub__()</span></code></a> methods.</p>
<div class="versionchanged">
<p><span class="versionmodified changed">Changed in version 3.14: </span>If only one operand is a complex number, the other operand is converted
to a floating-point number.</p>
</div>
</section>
<section id="shifting-operations">
<span id="shifting"></span><h2><span class="section-number">6.8. </span>Shifting operations<a class="headerlink" href="#shifting-operations" title="Link to this heading">¶</a></h2>
<p id="index-70">The shifting operations have lower priority than the arithmetic operations:</p>
<pre class="highlight">
<strong id="grammar-token-python-grammar-shift_expr">shift_expr</strong>: <a class="reference internal" href="#grammar-token-python-grammar-a_expr"><code class="xref docutils literal notranslate"><span class="pre">a_expr</span></code></a> | <a class="reference internal" href="#grammar-token-python-grammar-shift_expr"><code class="xref docutils literal notranslate"><span class="pre">shift_expr</span></code></a> (<span class="sx">&quot;&lt;&lt;&quot;</span> | <span class="sx">&quot;&gt;&gt;&quot;</span>) <a class="reference internal" href="#grammar-token-python-grammar-a_expr"><code class="xref docutils literal notranslate"><span class="pre">a_expr</span></code></a>
</pre>
<p>These operators accept integers as arguments.  They shift the first argument to
the left or right by the number of bits given by the second argument.</p>
<p>The left shift operation can be customized using the special <a class="reference internal" href="datamodel.html#object.__lshift__" title="object.__lshift__"><code class="xref py py-meth docutils literal notranslate"><span class="pre">__lshift__()</span></code></a>
and <a class="reference internal" href="datamodel.html#object.__rlshift__" title="object.__rlshift__"><code class="xref py py-meth docutils literal notranslate"><span class="pre">__rlshift__()</span></code></a> methods.
The right shift operation can be customized using the special <a class="reference internal" href="datamodel.html#object.__rshift__" title="object.__rshift__"><code class="xref py py-meth docutils literal notranslate"><span class="pre">__rshift__()</span></code></a>
and <a class="reference internal" href="datamodel.html#object.__rrshift__" title="object.__rrshift__"><code class="xref py py-meth docutils literal notranslate"><span class="pre">__rrshift__()</span></code></a> methods.</p>
<p id="index-71">A right shift by <em>n</em> bits is defined as floor division by <code class="docutils literal notranslate"><span class="pre">pow(2,n)</span></code>.  A left
shift by <em>n</em> bits is defined as multiplication with <code class="docutils literal notranslate"><span class="pre">pow(2,n)</span></code>.</p>
</section>
<section id="binary-bitwise-operations">
<span id="bitwise"></span><h2><span class="section-number">6.9. </span>Binary bitwise operations<a class="headerlink" href="#binary-bitwise-operations" title="Link to this heading">¶</a></h2>
<p id="index-72">Each of the three bitwise operations has a different priority level:</p>
<pre class="highlight">
<strong id="grammar-token-python-grammar-and_expr">and_expr</strong>: <a class="reference internal" href="#grammar-token-python-grammar-shift_expr"><code class="xref docutils literal notranslate"><span class="pre">shift_expr</span></code></a> | <a class="reference internal" href="#grammar-token-python-grammar-and_expr"><code class="xref docutils literal notranslate"><span class="pre">and_expr</span></code></a> <span class="sx">&quot;&amp;&quot;</span> <a class="reference internal" href="#grammar-token-python-grammar-shift_expr"><code class="xref docutils literal notranslate"><span class="pre">shift_expr</span></code></a>
<strong id="grammar-token-python-grammar-xor_expr">xor_expr</strong>: <a class="reference internal" href="#grammar-token-python-grammar-and_expr"><code class="xref docutils literal notranslate"><span class="pre">and_expr</span></code></a> | <a class="reference internal" href="#grammar-token-python-grammar-xor_expr"><code class="xref docutils literal notranslate"><span class="pre">xor_expr</span></code></a> <span class="sx">&quot;^&quot;</span> <a class="reference internal" href="#grammar-token-python-grammar-and_expr"><code class="xref docutils literal notranslate"><span class="pre">and_expr</span></code></a>
<strong id="grammar-token-python-grammar-or_expr">or_expr</strong>:  <a class="reference internal" href="#grammar-token-python-grammar-xor_expr"><code class="xref docutils literal notranslate"><span class="pre">xor_expr</span></code></a> | <a class="reference internal" href="#grammar-token-python-grammar-or_expr"><code class="xref docutils literal notranslate"><span class="pre">or_expr</span></code></a> <span class="sx">&quot;|&quot;</span> <a class="reference internal" href="#grammar-token-python-grammar-xor_expr"><code class="xref docutils literal notranslate"><span class="pre">xor_expr</span></code></a>
</pre>
<p id="index-73">The <code class="docutils literal notranslate"><span class="pre">&amp;</span></code> operator yields the bitwise AND of its arguments, which must be
integers or one of them must be a custom object overriding <a class="reference internal" href="datamodel.html#object.__and__" title="object.__and__"><code class="xref py py-meth docutils literal notranslate"><span class="pre">__and__()</span></code></a> or
<a class="reference internal" href="datamodel.html#object.__rand__" title="object.__rand__"><code class="xref py py-meth docutils literal notranslate"><span class="pre">__rand__()</span></code></a> special methods.</p>
<p id="index-74">The <code class="docutils literal notranslate"><span class="pre">^</span></code> operator yields the bitwise XOR (exclusive OR) of its arguments, which
must be integers or one of them must be a custom object overriding <a class="reference internal" href="datamodel.html#object.__xor__" title="object.__xor__"><code class="xref py py-meth docutils literal notranslate"><span class="pre">__xor__()</span></code></a> or
<a class="reference internal" href="datamodel.html#object.__rxor__" title="object.__rxor__"><code class="xref py py-meth docutils literal notranslate"><span class="pre">__rxor__()</span></code></a> special methods.</p>
<p id="index-75">The <code class="docutils literal notranslate"><span class="pre">|</span></code> operator yields the bitwise (inclusive) OR of its arguments, which
must be integers or one of them must be a custom object overriding <a class="reference internal" href="datamodel.html#object.__or__" title="object.__or__"><code class="xref py py-meth docutils literal notranslate"><span class="pre">__or__()</span></code></a> or
<a class="reference internal" href="datamodel.html#object.__ror__" title="object.__ror__"><code class="xref py py-meth docutils literal notranslate"><span class="pre">__ror__()</span></code></a> special methods.</p>
</section>
<section id="comparisons">
<span id="id11"></span><h2><span class="section-number">6.10. </span>Comparisons<a class="headerlink" href="#comparisons" title="Link to this heading">¶</a></h2>
<p id="index-76">Unlike C, all comparison operations in Python have the same priority, which is
lower than that of any arithmetic, shifting or bitwise operation.  Also unlike
C, expressions like <code class="docutils literal notranslate"><span class="pre">a</span> <span class="pre">&lt;</span> <span class="pre">b</span> <span class="pre">&lt;</span> <span class="pre">c</span></code> have the interpretation that is conventional
in mathematics:</p>
<pre class="highlight">
<strong id="grammar-token-python-grammar-comparison">comparison</strong>:    <a class="reference internal" href="#grammar-token-python-grammar-or_expr"><code class="xref docutils literal notranslate"><span class="pre">or_expr</span></code></a> (<a class="reference internal" href="#grammar-token-python-grammar-comp_operator"><code class="xref docutils literal notranslate"><span class="pre">comp_operator</span></code></a> <a class="reference internal" href="#grammar-token-python-grammar-or_expr"><code class="xref docutils literal notranslate"><span class="pre">or_expr</span></code></a>)*
<strong id="grammar-token-python-grammar-comp_operator">comp_operator</strong>: <span class="sx">&quot;&lt;&quot;</span> | <span class="sx">&quot;&gt;&quot;</span> | <span class="sx">&quot;==&quot;</span> | <span class="sx">&quot;&gt;=&quot;</span> | <span class="sx">&quot;&lt;=&quot;</span> | <span class="sx">&quot;!=&quot;</span>
               | <span class="sx">&quot;is&quot;</span> [<span class="sx">&quot;not&quot;</span>] | [<span class="sx">&quot;not&quot;</span>] <span class="sx">&quot;in&quot;</span>
</pre>
<p>Comparisons yield boolean values: <code class="docutils literal notranslate"><span class="pre">True</span></code> or <code class="docutils literal notranslate"><span class="pre">False</span></code>. Custom
<em class="dfn">rich comparison methods</em> may return non-boolean values. In this case
Python will call <a class="reference internal" href="../library/functions.html#bool" title="bool"><code class="xref py py-func docutils literal notranslate"><span class="pre">bool()</span></code></a> on such value in boolean contexts.</p>
<p id="index-77">Comparisons can be chained arbitrarily, e.g., <code class="docutils literal notranslate"><span class="pre">x</span> <span class="pre">&lt;</span> <span class="pre">y</span> <span class="pre">&lt;=</span> <span class="pre">z</span></code> is equivalent to
<code class="docutils literal notranslate"><span class="pre">x</span> <span class="pre">&lt;</span> <span class="pre">y</span> <span class="pre">and</span> <span class="pre">y</span> <span class="pre">&lt;=</span> <span class="pre">z</span></code>, except that <code class="docutils literal notranslate"><span class="pre">y</span></code> is evaluated only once (but in both
cases <code class="docutils literal notranslate"><span class="pre">z</span></code> is not evaluated at all when <code class="docutils literal notranslate"><span class="pre">x</span> <span class="pre">&lt;</span> <span class="pre">y</span></code> is found to be false).</p>
<p>Formally, if <em>a</em>, <em>b</em>, <em>c</em>, …, <em>y</em>, <em>z</em> are expressions and <em>op1</em>, <em>op2</em>, …,
<em>opN</em> are comparison operators, then <code class="docutils literal notranslate"><span class="pre">a</span> <span class="pre">op1</span> <span class="pre">b</span> <span class="pre">op2</span> <span class="pre">c</span> <span class="pre">...</span> <span class="pre">y</span> <span class="pre">opN</span> <span class="pre">z</span></code> is equivalent
to <code class="docutils literal notranslate"><span class="pre">a</span> <span class="pre">op1</span> <span class="pre">b</span> <span class="pre">and</span> <span class="pre">b</span> <span class="pre">op2</span> <span class="pre">c</span> <span class="pre">and</span> <span class="pre">...</span> <span class="pre">y</span> <span class="pre">opN</span> <span class="pre">z</span></code>, except that each expression is
evaluated at most once.</p>
<p>Note that <code class="docutils literal notranslate"><span class="pre">a</span> <span class="pre">op1</span> <span class="pre">b</span> <span class="pre">op2</span> <span class="pre">c</span></code> doesn’t imply any kind of comparison between <em>a</em> and
<em>c</em>, so that, e.g., <code class="docutils literal notranslate"><span class="pre">x</span> <span class="pre">&lt;</span> <span class="pre">y</span> <span class="pre">&gt;</span> <span class="pre">z</span></code> is perfectly legal (though perhaps not
pretty).</p>
<section id="value-comparisons">
<span id="expressions-value-comparisons"></span><h3><span class="section-number">6.10.1. </span>Value comparisons<a class="headerlink" href="#value-comparisons" title="Link to this heading">¶</a></h3>
<p>The operators <code class="docutils literal notranslate"><span class="pre">&lt;</span></code>, <code class="docutils literal notranslate"><span class="pre">&gt;</span></code>, <code class="docutils literal notranslate"><span class="pre">==</span></code>, <code class="docutils literal notranslate"><span class="pre">&gt;=</span></code>, <code class="docutils literal notranslate"><span class="pre">&lt;=</span></code>, and <code class="docutils literal notranslate"><span class="pre">!=</span></code> compare the
values of two objects.  The objects do not need to have the same type.</p>
<p>Chapter <a class="reference internal" href="datamodel.html#objects"><span class="std std-ref">Objects, values and types</span></a> states that objects have a value (in addition to type
and identity).  The value of an object is a rather abstract notion in Python:
For example, there is no canonical access method for an object’s value.  Also,
there is no requirement that the value of an object should be constructed in a
particular way, e.g. comprised of all its data attributes. Comparison operators
implement a particular notion of what the value of an object is.  One can think
of them as defining the value of an object indirectly, by means of their
comparison implementation.</p>
<p>Because all types are (direct or indirect) subtypes of <a class="reference internal" href="../library/functions.html#object" title="object"><code class="xref py py-class docutils literal notranslate"><span class="pre">object</span></code></a>, they
inherit the default comparison behavior from <code class="xref py py-class docutils literal notranslate"><span class="pre">object</span></code>.  Types can
customize their comparison behavior by implementing
<em class="dfn">rich comparison methods</em> like <a class="reference internal" href="datamodel.html#object.__lt__" title="object.__lt__"><code class="xref py py-meth docutils literal notranslate"><span class="pre">__lt__()</span></code></a>, described in
<a class="reference internal" href="datamodel.html#customization"><span class="std std-ref">Basic customization</span></a>.</p>
<p>The default behavior for equality comparison (<code class="docutils literal notranslate"><span class="pre">==</span></code> and <code class="docutils literal notranslate"><span class="pre">!=</span></code>) is based on
the identity of the objects.  Hence, equality comparison of instances with the
same identity results in equality, and equality comparison of instances with
different identities results in inequality.  A motivation for this default
behavior is the desire that all objects should be reflexive (i.e. <code class="docutils literal notranslate"><span class="pre">x</span> <span class="pre">is</span> <span class="pre">y</span></code>
implies <code class="docutils literal notranslate"><span class="pre">x</span> <span class="pre">==</span> <span class="pre">y</span></code>).</p>
<p>A default order comparison (<code class="docutils literal notranslate"><span class="pre">&lt;</span></code>, <code class="docutils literal notranslate"><span class="pre">&gt;</span></code>, <code class="docutils literal notranslate"><span class="pre">&lt;=</span></code>, and <code class="docutils literal notranslate"><span class="pre">&gt;=</span></code>) is not provided;
an attempt raises <a class="reference internal" href="../library/exceptions.html#TypeError" title="TypeError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">TypeError</span></code></a>.  A motivation for this default behavior is
the lack of a similar invariant as for equality.</p>
<p>The behavior of the default equality comparison, that instances with different
identities are always unequal, may be in contrast to what types will need that
have a sensible definition of object value and value-based equality.  Such
types will need to customize their comparison behavior, and in fact, a number
of built-in types have done that.</p>
<p>The following list describes the comparison behavior of the most important
built-in types.</p>
<ul>
<li><p>Numbers of built-in numeric types (<a class="reference internal" href="../library/stdtypes.html#typesnumeric"><span class="std std-ref">Numeric Types — int, float, complex</span></a>) and of the standard
library types <a class="reference internal" href="../library/fractions.html#fractions.Fraction" title="fractions.Fraction"><code class="xref py py-class docutils literal notranslate"><span class="pre">fractions.Fraction</span></code></a> and <a class="reference internal" href="../library/decimal.html#decimal.Decimal" title="decimal.Decimal"><code class="xref py py-class docutils literal notranslate"><span class="pre">decimal.Decimal</span></code></a> can be
compared within and across their types, with the restriction that complex
numbers do not support order comparison.  Within the limits of the types
involved, they compare mathematically (algorithmically) correct without loss
of precision.</p>
<p>The not-a-number values <code class="docutils literal notranslate"><span class="pre">float('NaN')</span></code> and <code class="docutils literal notranslate"><span class="pre">decimal.Decimal('NaN')</span></code> are
special.  Any ordered comparison of a number to a not-a-number value is false.
A counter-intuitive implication is that not-a-number values are not equal to
themselves.  For example, if <code class="docutils literal notranslate"><span class="pre">x</span> <span class="pre">=</span> <span class="pre">float('NaN')</span></code>, <code class="docutils literal notranslate"><span class="pre">3</span> <span class="pre">&lt;</span> <span class="pre">x</span></code>, <code class="docutils literal notranslate"><span class="pre">x</span> <span class="pre">&lt;</span> <span class="pre">3</span></code> and
<code class="docutils literal notranslate"><span class="pre">x</span> <span class="pre">==</span> <span class="pre">x</span></code> are all false, while <code class="docutils literal notranslate"><span class="pre">x</span> <span class="pre">!=</span> <span class="pre">x</span></code> is true.  This behavior is
compliant with IEEE 754.</p>
</li>
<li><p><code class="docutils literal notranslate"><span class="pre">None</span></code> and <a class="reference internal" href="../library/constants.html#NotImplemented" title="NotImplemented"><code class="xref py py-data docutils literal notranslate"><span class="pre">NotImplemented</span></code></a> are singletons.  <span class="target" id="index-78"></span><a class="pep reference external" href="https://peps.python.org/pep-0008/"><strong>PEP 8</strong></a> advises that
comparisons for singletons should always be done with <code class="docutils literal notranslate"><span class="pre">is</span></code> or <code class="docutils literal notranslate"><span class="pre">is</span> <span class="pre">not</span></code>,
never the equality operators.</p></li>
<li><p>Binary sequences (instances of <a class="reference internal" href="../library/stdtypes.html#bytes" title="bytes"><code class="xref py py-class docutils literal notranslate"><span class="pre">bytes</span></code></a> or <a class="reference internal" href="../library/stdtypes.html#bytearray" title="bytearray"><code class="xref py py-class docutils literal notranslate"><span class="pre">bytearray</span></code></a>) can be
compared within and across their types.  They compare lexicographically using
the numeric values of their elements.</p></li>
<li><p>Strings (instances of <a class="reference internal" href="../library/stdtypes.html#str" title="str"><code class="xref py py-class docutils literal notranslate"><span class="pre">str</span></code></a>) compare lexicographically using the
numerical Unicode code points (the result of the built-in function
<a class="reference internal" href="../library/functions.html#ord" title="ord"><code class="xref py py-func docutils literal notranslate"><span class="pre">ord()</span></code></a>) of their characters. <a class="footnote-reference brackets" href="#id20" id="id12" role="doc-noteref"><span class="fn-bracket">[</span>3<span class="fn-bracket">]</span></a></p>
<p>Strings and binary sequences cannot be directly compared.</p>
</li>
<li><p>Sequences (instances of <a class="reference internal" href="../library/stdtypes.html#tuple" title="tuple"><code class="xref py py-class docutils literal notranslate"><span class="pre">tuple</span></code></a>, <a class="reference internal" href="../library/stdtypes.html#list" title="list"><code class="xref py py-class docutils literal notranslate"><span class="pre">list</span></code></a>, or <a class="reference internal" href="../library/stdtypes.html#range" title="range"><code class="xref py py-class docutils literal notranslate"><span class="pre">range</span></code></a>) can
be compared only within each of their types, with the restriction that ranges
do not support order comparison.  Equality comparison across these types
results in inequality, and ordering comparison across these types raises
<a class="reference internal" href="../library/exceptions.html#TypeError" title="TypeError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">TypeError</span></code></a>.</p>
<p>Sequences compare lexicographically using comparison of corresponding
elements.  The built-in containers typically assume identical objects are
equal to themselves.  That lets them bypass equality tests for identical
objects to improve performance and to maintain their internal invariants.</p>
<p>Lexicographical comparison between built-in collections works as follows:</p>
<ul class="simple">
<li><p>For two collections to compare equal, they must be of the same type, have
the same length, and each pair of corresponding elements must compare
equal (for example, <code class="docutils literal notranslate"><span class="pre">[1,2]</span> <span class="pre">==</span> <span class="pre">(1,2)</span></code> is false because the type is not the
same).</p></li>
<li><p>Collections that support order comparison are ordered the same as their
first unequal elements (for example, <code class="docutils literal notranslate"><span class="pre">[1,2,x]</span> <span class="pre">&lt;=</span> <span class="pre">[1,2,y]</span></code> has the same
value as <code class="docutils literal notranslate"><span class="pre">x</span> <span class="pre">&lt;=</span> <span class="pre">y</span></code>).  If a corresponding element does not exist, the
shorter collection is ordered first (for example, <code class="docutils literal notranslate"><span class="pre">[1,2]</span> <span class="pre">&lt;</span> <span class="pre">[1,2,3]</span></code> is
true).</p></li>
</ul>
</li>
<li><p>Mappings (instances of <a class="reference internal" href="../library/stdtypes.html#dict" title="dict"><code class="xref py py-class docutils literal notranslate"><span class="pre">dict</span></code></a>) compare equal if and only if they have
equal <code class="docutils literal notranslate"><span class="pre">(key,</span> <span class="pre">value)</span></code> pairs. Equality comparison of the keys and values
enforces reflexivity.</p>
<p>Order comparisons (<code class="docutils literal notranslate"><span class="pre">&lt;</span></code>, <code class="docutils literal notranslate"><span class="pre">&gt;</span></code>, <code class="docutils literal notranslate"><span class="pre">&lt;=</span></code>, and <code class="docutils literal notranslate"><span class="pre">&gt;=</span></code>) raise <a class="reference internal" href="../library/exceptions.html#TypeError" title="TypeError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">TypeError</span></code></a>.</p>
</li>
<li><p>Sets (instances of <a class="reference internal" href="../library/stdtypes.html#set" title="set"><code class="xref py py-class docutils literal notranslate"><span class="pre">set</span></code></a> or <a class="reference internal" href="../library/stdtypes.html#frozenset" title="frozenset"><code class="xref py py-class docutils literal notranslate"><span class="pre">frozenset</span></code></a>) can be compared within
and across their types.</p>
<p>They define order
comparison operators to mean subset and superset tests.  Those relations do
not define total orderings (for example, the two sets <code class="docutils literal notranslate"><span class="pre">{1,2}</span></code> and <code class="docutils literal notranslate"><span class="pre">{2,3}</span></code>
are not equal, nor subsets of one another, nor supersets of one
another).  Accordingly, sets are not appropriate arguments for functions
which depend on total ordering (for example, <a class="reference internal" href="../library/functions.html#min" title="min"><code class="xref py py-func docutils literal notranslate"><span class="pre">min()</span></code></a>, <a class="reference internal" href="../library/functions.html#max" title="max"><code class="xref py py-func docutils literal notranslate"><span class="pre">max()</span></code></a>, and
<a class="reference internal" href="../library/functions.html#sorted" title="sorted"><code class="xref py py-func docutils literal notranslate"><span class="pre">sorted()</span></code></a> produce undefined results given a list of sets as inputs).</p>
<p>Comparison of sets enforces reflexivity of its elements.</p>
</li>
<li><p>Most other built-in types have no comparison methods implemented, so they
inherit the default comparison behavior.</p></li>
</ul>
<p>User-defined classes that customize their comparison behavior should follow
some consistency rules, if possible:</p>
<ul>
<li><p>Equality comparison should be reflexive.
In other words, identical objects should compare equal:</p>
<blockquote>
<div><p><code class="docutils literal notranslate"><span class="pre">x</span> <span class="pre">is</span> <span class="pre">y</span></code> implies <code class="docutils literal notranslate"><span class="pre">x</span> <span class="pre">==</span> <span class="pre">y</span></code></p>
</div></blockquote>
</li>
<li><p>Comparison should be symmetric.
In other words, the following expressions should have the same result:</p>
<blockquote>
<div><p><code class="docutils literal notranslate"><span class="pre">x</span> <span class="pre">==</span> <span class="pre">y</span></code> and <code class="docutils literal notranslate"><span class="pre">y</span> <span class="pre">==</span> <span class="pre">x</span></code></p>
<p><code class="docutils literal notranslate"><span class="pre">x</span> <span class="pre">!=</span> <span class="pre">y</span></code> and <code class="docutils literal notranslate"><span class="pre">y</span> <span class="pre">!=</span> <span class="pre">x</span></code></p>
<p><code class="docutils literal notranslate"><span class="pre">x</span> <span class="pre">&lt;</span> <span class="pre">y</span></code> and <code class="docutils literal notranslate"><span class="pre">y</span> <span class="pre">&gt;</span> <span class="pre">x</span></code></p>
<p><code class="docutils literal notranslate"><span class="pre">x</span> <span class="pre">&lt;=</span> <span class="pre">y</span></code> and <code class="docutils literal notranslate"><span class="pre">y</span> <span class="pre">&gt;=</span> <span class="pre">x</span></code></p>
</div></blockquote>
</li>
<li><p>Comparison should be transitive.
The following (non-exhaustive) examples illustrate that:</p>
<blockquote>
<div><p><code class="docutils literal notranslate"><span class="pre">x</span> <span class="pre">&gt;</span> <span class="pre">y</span> <span class="pre">and</span> <span class="pre">y</span> <span class="pre">&gt;</span> <span class="pre">z</span></code> implies <code class="docutils literal notranslate"><span class="pre">x</span> <span class="pre">&gt;</span> <span class="pre">z</span></code></p>
<p><code class="docutils literal notranslate"><span class="pre">x</span> <span class="pre">&lt;</span> <span class="pre">y</span> <span class="pre">and</span> <span class="pre">y</span> <span class="pre">&lt;=</span> <span class="pre">z</span></code> implies <code class="docutils literal notranslate"><span class="pre">x</span> <span class="pre">&lt;</span> <span class="pre">z</span></code></p>
</div></blockquote>
</li>
<li><p>Inverse comparison should result in the boolean negation.
In other words, the following expressions should have the same result:</p>
<blockquote>
<div><p><code class="docutils literal notranslate"><span class="pre">x</span> <span class="pre">==</span> <span class="pre">y</span></code> and <code class="docutils literal notranslate"><span class="pre">not</span> <span class="pre">x</span> <span class="pre">!=</span> <span class="pre">y</span></code></p>
<p><code class="docutils literal notranslate"><span class="pre">x</span> <span class="pre">&lt;</span> <span class="pre">y</span></code> and <code class="docutils literal notranslate"><span class="pre">not</span> <span class="pre">x</span> <span class="pre">&gt;=</span> <span class="pre">y</span></code> (for total ordering)</p>
<p><code class="docutils literal notranslate"><span class="pre">x</span> <span class="pre">&gt;</span> <span class="pre">y</span></code> and <code class="docutils literal notranslate"><span class="pre">not</span> <span class="pre">x</span> <span class="pre">&lt;=</span> <span class="pre">y</span></code> (for total ordering)</p>
</div></blockquote>
<p>The last two expressions apply to totally ordered collections (e.g. to
sequences, but not to sets or mappings). See also the
<a class="reference internal" href="../library/functools.html#functools.total_ordering" title="functools.total_ordering"><code class="xref py py-func docutils literal notranslate"><span class="pre">total_ordering()</span></code></a> decorator.</p>
</li>
<li><p>The <a class="reference internal" href="../library/functions.html#hash" title="hash"><code class="xref py py-func docutils literal notranslate"><span class="pre">hash()</span></code></a> result should be consistent with equality.
Objects that are equal should either have the same hash value,
or be marked as unhashable.</p></li>
</ul>
<p>Python does not enforce these consistency rules. In fact, the not-a-number
values are an example for not following these rules.</p>
</section>
<section id="membership-test-operations">
<span id="membership-test-details"></span><span id="not-in"></span><span id="in"></span><h3><span class="section-number">6.10.2. </span>Membership test operations<a class="headerlink" href="#membership-test-operations" title="Link to this heading">¶</a></h3>
<p>The operators <a class="reference internal" href="#in"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">in</span></code></a> and <a class="reference internal" href="#not-in"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">not</span> <span class="pre">in</span></code></a> test for membership.  <code class="docutils literal notranslate"><span class="pre">x</span> <span class="pre">in</span>
<span class="pre">s</span></code> evaluates to <code class="docutils literal notranslate"><span class="pre">True</span></code> if <em>x</em> is a member of <em>s</em>, and <code class="docutils literal notranslate"><span class="pre">False</span></code> otherwise.
<code class="docutils literal notranslate"><span class="pre">x</span> <span class="pre">not</span> <span class="pre">in</span> <span class="pre">s</span></code> returns the negation of <code class="docutils literal notranslate"><span class="pre">x</span> <span class="pre">in</span> <span class="pre">s</span></code>.  All built-in sequences and
set types support this as well as dictionary, for which <code class="xref std std-keyword docutils literal notranslate"><span class="pre">in</span></code> tests
whether the dictionary has a given key. For container types such as list, tuple,
set, frozenset, dict, or collections.deque, the expression <code class="docutils literal notranslate"><span class="pre">x</span> <span class="pre">in</span> <span class="pre">y</span></code> is equivalent
to <code class="docutils literal notranslate"><span class="pre">any(x</span> <span class="pre">is</span> <span class="pre">e</span> <span class="pre">or</span> <span class="pre">x</span> <span class="pre">==</span> <span class="pre">e</span> <span class="pre">for</span> <span class="pre">e</span> <span class="pre">in</span> <span class="pre">y)</span></code>.</p>
<p>For the string and bytes types, <code class="docutils literal notranslate"><span class="pre">x</span> <span class="pre">in</span> <span class="pre">y</span></code> is <code class="docutils literal notranslate"><span class="pre">True</span></code> if and only if <em>x</em> is a
substring of <em>y</em>.  An equivalent test is <code class="docutils literal notranslate"><span class="pre">y.find(x)</span> <span class="pre">!=</span> <span class="pre">-1</span></code>.  Empty strings are
always considered to be a substring of any other string, so <code class="docutils literal notranslate"><span class="pre">&quot;&quot;</span> <span class="pre">in</span> <span class="pre">&quot;abc&quot;</span></code> will
return <code class="docutils literal notranslate"><span class="pre">True</span></code>.</p>
<p>For user-defined classes which define the <a class="reference internal" href="datamodel.html#object.__contains__" title="object.__contains__"><code class="xref py py-meth docutils literal notranslate"><span class="pre">__contains__()</span></code></a> method, <code class="docutils literal notranslate"><span class="pre">x</span> <span class="pre">in</span>
<span class="pre">y</span></code> returns <code class="docutils literal notranslate"><span class="pre">True</span></code> if <code class="docutils literal notranslate"><span class="pre">y.__contains__(x)</span></code> returns a true value, and
<code class="docutils literal notranslate"><span class="pre">False</span></code> otherwise.</p>
<p>For user-defined classes which do not define <a class="reference internal" href="datamodel.html#object.__contains__" title="object.__contains__"><code class="xref py py-meth docutils literal notranslate"><span class="pre">__contains__()</span></code></a> but do define
<a class="reference internal" href="datamodel.html#object.__iter__" title="object.__iter__"><code class="xref py py-meth docutils literal notranslate"><span class="pre">__iter__()</span></code></a>, <code class="docutils literal notranslate"><span class="pre">x</span> <span class="pre">in</span> <span class="pre">y</span></code> is <code class="docutils literal notranslate"><span class="pre">True</span></code> if some value <code class="docutils literal notranslate"><span class="pre">z</span></code>, for which the
expression <code class="docutils literal notranslate"><span class="pre">x</span> <span class="pre">is</span> <span class="pre">z</span> <span class="pre">or</span> <span class="pre">x</span> <span class="pre">==</span> <span class="pre">z</span></code> is true, is produced while iterating over <code class="docutils literal notranslate"><span class="pre">y</span></code>.
If an exception is raised during the iteration, it is as if <a class="reference internal" href="#in"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">in</span></code></a> raised
that exception.</p>
<p>Lastly, the old-style iteration protocol is tried: if a class defines
<a class="reference internal" href="datamodel.html#object.__getitem__" title="object.__getitem__"><code class="xref py py-meth docutils literal notranslate"><span class="pre">__getitem__()</span></code></a>, <code class="docutils literal notranslate"><span class="pre">x</span> <span class="pre">in</span> <span class="pre">y</span></code> is <code class="docutils literal notranslate"><span class="pre">True</span></code> if and only if there is a non-negative
integer index <em>i</em> such that <code class="docutils literal notranslate"><span class="pre">x</span> <span class="pre">is</span> <span class="pre">y[i]</span> <span class="pre">or</span> <span class="pre">x</span> <span class="pre">==</span> <span class="pre">y[i]</span></code>, and no lower integer index
raises the <a class="reference internal" href="../library/exceptions.html#IndexError" title="IndexError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">IndexError</span></code></a> exception.  (If any other exception is raised, it is as
if <a class="reference internal" href="#in"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">in</span></code></a> raised that exception).</p>
<p id="index-79">The operator <a class="reference internal" href="#not-in"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">not</span> <span class="pre">in</span></code></a> is defined to have the inverse truth value of
<a class="reference internal" href="#in"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">in</span></code></a>.</p>
</section>
<section id="is-not">
<span id="is"></span><span id="index-80"></span><span id="identity-comparisons"></span><h3><span class="section-number">6.10.3. </span>Identity comparisons<a class="headerlink" href="#is-not" title="Link to this heading">¶</a></h3>
<p>The operators <a class="reference internal" href="#is"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">is</span></code></a> and <a class="reference internal" href="#is-not"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">is</span> <span class="pre">not</span></code></a> test for an object’s identity: <code class="docutils literal notranslate"><span class="pre">x</span>
<span class="pre">is</span> <span class="pre">y</span></code> is true if and only if <em>x</em> and <em>y</em> are the same object.  An Object’s identity
is determined using the <a class="reference internal" href="../library/functions.html#id" title="id"><code class="xref py py-meth docutils literal notranslate"><span class="pre">id()</span></code></a> function.  <code class="docutils literal notranslate"><span class="pre">x</span> <span class="pre">is</span> <span class="pre">not</span> <span class="pre">y</span></code> yields the inverse
truth value. <a class="footnote-reference brackets" href="#id21" id="id13" role="doc-noteref"><span class="fn-bracket">[</span>4<span class="fn-bracket">]</span></a></p>
</section>
</section>
<section id="boolean-operations">
<span id="not"></span><span id="or"></span><span id="and"></span><span id="booleans"></span><h2><span class="section-number">6.11. </span>Boolean operations<a class="headerlink" href="#boolean-operations" title="Link to this heading">¶</a></h2>
<pre class="highlight" id="index-81">
<strong id="grammar-token-python-grammar-or_test">or_test</strong>:  <a class="reference internal" href="#grammar-token-python-grammar-and_test"><code class="xref docutils literal notranslate"><span class="pre">and_test</span></code></a> | <a class="reference internal" href="#grammar-token-python-grammar-or_test"><code class="xref docutils literal notranslate"><span class="pre">or_test</span></code></a> <span class="sx">&quot;or&quot;</span> <a class="reference internal" href="#grammar-token-python-grammar-and_test"><code class="xref docutils literal notranslate"><span class="pre">and_test</span></code></a>
<strong id="grammar-token-python-grammar-and_test">and_test</strong>: <a class="reference internal" href="#grammar-token-python-grammar-not_test"><code class="xref docutils literal notranslate"><span class="pre">not_test</span></code></a> | <a class="reference internal" href="#grammar-token-python-grammar-and_test"><code class="xref docutils literal notranslate"><span class="pre">and_test</span></code></a> <span class="sx">&quot;and&quot;</span> <a class="reference internal" href="#grammar-token-python-grammar-not_test"><code class="xref docutils literal notranslate"><span class="pre">not_test</span></code></a>
<strong id="grammar-token-python-grammar-not_test">not_test</strong>: <a class="reference internal" href="#grammar-token-python-grammar-comparison"><code class="xref docutils literal notranslate"><span class="pre">comparison</span></code></a> | <span class="sx">&quot;not&quot;</span> <a class="reference internal" href="#grammar-token-python-grammar-not_test"><code class="xref docutils literal notranslate"><span class="pre">not_test</span></code></a>
</pre>
<p>In the context of Boolean operations, and also when expressions are used by
control flow statements, the following values are interpreted as false:
<code class="docutils literal notranslate"><span class="pre">False</span></code>, <code class="docutils literal notranslate"><span class="pre">None</span></code>, numeric zero of all types, and empty strings and containers
(including strings, tuples, lists, dictionaries, sets and frozensets).  All
other values are interpreted as true.  User-defined objects can customize their
truth value by providing a <a class="reference internal" href="datamodel.html#object.__bool__" title="object.__bool__"><code class="xref py py-meth docutils literal notranslate"><span class="pre">__bool__()</span></code></a> method.</p>
<p id="index-82">The operator <a class="reference internal" href="#not"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">not</span></code></a> yields <code class="docutils literal notranslate"><span class="pre">True</span></code> if its argument is false, <code class="docutils literal notranslate"><span class="pre">False</span></code>
otherwise.</p>
<p id="index-83">The expression <code class="docutils literal notranslate"><span class="pre">x</span> <span class="pre">and</span> <span class="pre">y</span></code> first evaluates <em>x</em>; if <em>x</em> is false, its value is
returned; otherwise, <em>y</em> is evaluated and the resulting value is returned.</p>
<p id="index-84">The expression <code class="docutils literal notranslate"><span class="pre">x</span> <span class="pre">or</span> <span class="pre">y</span></code> first evaluates <em>x</em>; if <em>x</em> is true, its value is
returned; otherwise, <em>y</em> is evaluated and the resulting value is returned.</p>
<p>Note that neither <a class="reference internal" href="#and"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">and</span></code></a> nor <a class="reference internal" href="#or"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">or</span></code></a> restrict the value and type
they return to <code class="docutils literal notranslate"><span class="pre">False</span></code> and <code class="docutils literal notranslate"><span class="pre">True</span></code>, but rather return the last evaluated
argument.  This is sometimes useful, e.g., if <code class="docutils literal notranslate"><span class="pre">s</span></code> is a string that should be
replaced by a default value if it is empty, the expression <code class="docutils literal notranslate"><span class="pre">s</span> <span class="pre">or</span> <span class="pre">'foo'</span></code> yields
the desired value.  Because <a class="reference internal" href="#not"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">not</span></code></a> has to create a new value, it
returns a boolean value regardless of the type of its argument
(for example, <code class="docutils literal notranslate"><span class="pre">not</span> <span class="pre">'foo'</span></code> produces <code class="docutils literal notranslate"><span class="pre">False</span></code> rather than <code class="docutils literal notranslate"><span class="pre">''</span></code>.)</p>
</section>
<section id="assignment-expressions">
<span id="index-85"></span><span id="id14"></span><h2><span class="section-number">6.12. </span>Assignment expressions<a class="headerlink" href="#assignment-expressions" title="Link to this heading">¶</a></h2>
<pre class="highlight">
<strong id="grammar-token-python-grammar-assignment_expression">assignment_expression</strong>: [<a class="reference internal" href="lexical_analysis.html#grammar-token-python-grammar-identifier"><code class="xref docutils literal notranslate"><span class="pre">identifier</span></code></a> <span class="sx">&quot;:=&quot;</span>] <a class="reference internal" href="#grammar-token-python-grammar-expression"><code class="xref docutils literal notranslate"><span class="pre">expression</span></code></a>
</pre>
<p>An assignment expression (sometimes also called a “named expression” or
“walrus”) assigns an <a class="reference internal" href="#grammar-token-python-grammar-expression"><code class="xref std std-token docutils literal notranslate"><span class="pre">expression</span></code></a> to an
<a class="reference internal" href="lexical_analysis.html#grammar-token-python-grammar-identifier"><code class="xref std std-token docutils literal notranslate"><span class="pre">identifier</span></code></a>, while also returning the value of the
<code class="xref std std-token docutils literal notranslate"><span class="pre">expression</span></code>.</p>
<p>One common use case is when handling matched regular expressions:</p>
<div class="highlight-python notranslate"><div class="highlight"><pre><span></span><span class="k">if</span> <span class="n">matching</span> <span class="o">:=</span> <span class="n">pattern</span><span class="o">.</span><span class="n">search</span><span class="p">(</span><span class="n">data</span><span class="p">):</span>
    <span class="n">do_something</span><span class="p">(</span><span class="n">matching</span><span class="p">)</span>
</pre></div>
</div>
<p>Or, when processing a file stream in chunks:</p>
<div class="highlight-python notranslate"><div class="highlight"><pre><span></span><span class="k">while</span> <span class="n">chunk</span> <span class="o">:=</span> <span class="n">file</span><span class="o">.</span><span class="n">read</span><span class="p">(</span><span class="mi">9000</span><span class="p">):</span>
    <span class="n">process</span><span class="p">(</span><span class="n">chunk</span><span class="p">)</span>
</pre></div>
</div>
<p>Assignment expressions must be surrounded by parentheses when
used as expression statements and when used as sub-expressions in
slicing, conditional, lambda,
keyword-argument, and comprehension-if expressions and
in <code class="docutils literal notranslate"><span class="pre">assert</span></code>, <code class="docutils literal notranslate"><span class="pre">with</span></code>, and <code class="docutils literal notranslate"><span class="pre">assignment</span></code> statements.
In all other places where they can be used, parentheses are not required,
including in <code class="docutils literal notranslate"><span class="pre">if</span></code> and <code class="docutils literal notranslate"><span class="pre">while</span></code> statements.</p>
<div class="versionadded">
<p><span class="versionmodified added">Added in version 3.8: </span>See <span class="target" id="index-86"></span><a class="pep reference external" href="https://peps.python.org/pep-0572/"><strong>PEP 572</strong></a> for more details about assignment expressions.</p>
</div>
</section>
<section id="conditional-expressions">
<span id="if-expr"></span><h2><span class="section-number">6.13. </span>Conditional expressions<a class="headerlink" href="#conditional-expressions" title="Link to this heading">¶</a></h2>
<pre class="highlight" id="index-87">
<strong id="grammar-token-python-grammar-conditional_expression">conditional_expression</strong>: <a class="reference internal" href="#grammar-token-python-grammar-or_test"><code class="xref docutils literal notranslate"><span class="pre">or_test</span></code></a> [<span class="sx">&quot;if&quot;</span> <a class="reference internal" href="#grammar-token-python-grammar-or_test"><code class="xref docutils literal notranslate"><span class="pre">or_test</span></code></a> <span class="sx">&quot;else&quot;</span> <a class="reference internal" href="#grammar-token-python-grammar-expression"><code class="xref docutils literal notranslate"><span class="pre">expression</span></code></a>]
<strong id="grammar-token-python-grammar-expression">expression</strong>:             <a class="reference internal" href="#grammar-token-python-grammar-conditional_expression"><code class="xref docutils literal notranslate"><span class="pre">conditional_expression</span></code></a> | <a class="reference internal" href="#grammar-token-python-grammar-lambda_expr"><code class="xref docutils literal notranslate"><span class="pre">lambda_expr</span></code></a>
</pre>
<p>A conditional expression (sometimes called a “ternary operator”) is an
alternative to the if-else statement. As it is an expression, it returns a value
and can appear as a sub-expression.</p>
<p>The expression <code class="docutils literal notranslate"><span class="pre">x</span> <span class="pre">if</span> <span class="pre">C</span> <span class="pre">else</span> <span class="pre">y</span></code> first evaluates the condition, <em>C</em> rather than <em>x</em>.
If <em>C</em> is true, <em>x</em> is evaluated and its value is returned; otherwise, <em>y</em> is
evaluated and its value is returned.</p>
<p>See <span class="target" id="index-88"></span><a class="pep reference external" href="https://peps.python.org/pep-0308/"><strong>PEP 308</strong></a> for more details about conditional expressions.</p>
</section>
<section id="lambda">
<span id="lambdas"></span><span id="id15"></span><h2><span class="section-number">6.14. </span>Lambdas<a class="headerlink" href="#lambda" title="Link to this heading">¶</a></h2>
<pre class="highlight" id="index-89">
<strong id="grammar-token-python-grammar-lambda_expr">lambda_expr</strong>: <span class="sx">&quot;lambda&quot;</span> [<a class="reference internal" href="compound_stmts.html#grammar-token-python-grammar-parameter_list"><code class="xref docutils literal notranslate"><span class="pre">parameter_list</span></code></a>] <span class="sx">&quot;:&quot;</span> <a class="reference internal" href="#grammar-token-python-grammar-expression"><code class="xref docutils literal notranslate"><span class="pre">expression</span></code></a>
</pre>
<p>Lambda expressions (sometimes called lambda forms) are used to create anonymous
functions. The expression <code class="docutils literal notranslate"><span class="pre">lambda</span> <span class="pre">parameters:</span> <span class="pre">expression</span></code> yields a function
object.  The unnamed object behaves like a function object defined with:</p>
<div class="highlight-none notranslate"><div class="highlight"><pre><span></span>def &lt;lambda&gt;(parameters):
    return expression
</pre></div>
</div>
<p>See section <a class="reference internal" href="compound_stmts.html#function"><span class="std std-ref">Function definitions</span></a> for the syntax of parameter lists.  Note that
functions created with lambda expressions cannot contain statements or
annotations.</p>
</section>
<section id="expression-lists">
<span id="exprlists"></span><h2><span class="section-number">6.15. </span>Expression lists<a class="headerlink" href="#expression-lists" title="Link to this heading">¶</a></h2>
<pre class="highlight" id="index-90">
<strong id="grammar-token-python-grammar-starred_expression">starred_expression</strong>:       <span class="sx">&quot;*&quot;</span> <a class="reference internal" href="#grammar-token-python-grammar-or_expr"><code class="xref docutils literal notranslate"><span class="pre">or_expr</span></code></a> | <a class="reference internal" href="#grammar-token-python-grammar-expression"><code class="xref docutils literal notranslate"><span class="pre">expression</span></code></a>
<strong id="grammar-token-python-grammar-flexible_expression">flexible_expression</strong>:      <a class="reference internal" href="#grammar-token-python-grammar-assignment_expression"><code class="xref docutils literal notranslate"><span class="pre">assignment_expression</span></code></a> | <a class="reference internal" href="#grammar-token-python-grammar-starred_expression"><code class="xref docutils literal notranslate"><span class="pre">starred_expression</span></code></a>
<strong id="grammar-token-python-grammar-flexible_expression_list">flexible_expression_list</strong>: <a class="reference internal" href="#grammar-token-python-grammar-flexible_expression"><code class="xref docutils literal notranslate"><span class="pre">flexible_expression</span></code></a> (<span class="sx">&quot;,&quot;</span> <a class="reference internal" href="#grammar-token-python-grammar-flexible_expression"><code class="xref docutils literal notranslate"><span class="pre">flexible_expression</span></code></a>)* [<span class="sx">&quot;,&quot;</span>]
<strong id="grammar-token-python-grammar-starred_expression_list">starred_expression_list</strong>:  <a class="reference internal" href="#grammar-token-python-grammar-starred_expression"><code class="xref docutils literal notranslate"><span class="pre">starred_expression</span></code></a> (<span class="sx">&quot;,&quot;</span> <a class="reference internal" href="#grammar-token-python-grammar-starred_expression"><code class="xref docutils literal notranslate"><span class="pre">starred_expression</span></code></a>)* [<span class="sx">&quot;,&quot;</span>]
<strong id="grammar-token-python-grammar-expression_list">expression_list</strong>:          <a class="reference internal" href="#grammar-token-python-grammar-expression"><code class="xref docutils literal notranslate"><span class="pre">expression</span></code></a> (<span class="sx">&quot;,&quot;</span> <a class="reference internal" href="#grammar-token-python-grammar-expression"><code class="xref docutils literal notranslate"><span class="pre">expression</span></code></a>)* [<span class="sx">&quot;,&quot;</span>]
<strong id="grammar-token-python-grammar-yield_list">yield_list</strong>:               <a class="reference internal" href="#grammar-token-python-grammar-expression_list"><code class="xref docutils literal notranslate"><span class="pre">expression_list</span></code></a> | <a class="reference internal" href="#grammar-token-python-grammar-starred_expression"><code class="xref docutils literal notranslate"><span class="pre">starred_expression</span></code></a> <span class="sx">&quot;,&quot;</span> [<a class="reference internal" href="#grammar-token-python-grammar-starred_expression_list"><code class="xref docutils literal notranslate"><span class="pre">starred_expression_list</span></code></a>]
</pre>
<p id="index-91">Except when part of a list or set display, an expression list
containing at least one comma yields a tuple.  The length of
the tuple is the number of expressions in the list.  The expressions are
evaluated from left to right.</p>
<p id="index-92">An asterisk <code class="docutils literal notranslate"><span class="pre">*</span></code> denotes <em class="dfn">iterable unpacking</em>.  Its operand must be
an <a class="reference internal" href="../glossary.html#term-iterable"><span class="xref std std-term">iterable</span></a>.  The iterable is expanded into a sequence of items,
which are included in the new tuple, list, or set, at the site of
the unpacking.</p>
<div class="versionadded">
<p><span class="versionmodified added">Added in version 3.5: </span>Iterable unpacking in expression lists, originally proposed by <span class="target" id="index-93"></span><a class="pep reference external" href="https://peps.python.org/pep-0448/"><strong>PEP 448</strong></a>.</p>
</div>
<div class="versionadded">
<p><span class="versionmodified added">Added in version 3.11: </span>Any item in an expression list may be starred. See <span class="target" id="index-94"></span><a class="pep reference external" href="https://peps.python.org/pep-0646/"><strong>PEP 646</strong></a>.</p>
</div>
<p id="index-95">A trailing comma is required only to create a one-item tuple,
such as <code class="docutils literal notranslate"><span class="pre">1,</span></code>; it is optional in all other cases.
A single expression without a
trailing comma doesn’t create a tuple, but rather yields the value of that
expression. (To create an empty tuple, use an empty pair of parentheses:
<code class="docutils literal notranslate"><span class="pre">()</span></code>.)</p>
</section>
<section id="evaluation-order">
<span id="evalorder"></span><h2><span class="section-number">6.16. </span>Evaluation order<a class="headerlink" href="#evaluation-order" title="Link to this heading">¶</a></h2>
<p id="index-96">Python evaluates expressions from left to right.  Notice that while evaluating
an assignment, the right-hand side is evaluated before the left-hand side.</p>
<p>In the following lines, expressions will be evaluated in the arithmetic order of
their suffixes:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="n">expr1</span><span class="p">,</span> <span class="n">expr2</span><span class="p">,</span> <span class="n">expr3</span><span class="p">,</span> <span class="n">expr4</span>
<span class="p">(</span><span class="n">expr1</span><span class="p">,</span> <span class="n">expr2</span><span class="p">,</span> <span class="n">expr3</span><span class="p">,</span> <span class="n">expr4</span><span class="p">)</span>
<span class="p">{</span><span class="n">expr1</span><span class="p">:</span> <span class="n">expr2</span><span class="p">,</span> <span class="n">expr3</span><span class="p">:</span> <span class="n">expr4</span><span class="p">}</span>
<span class="n">expr1</span> <span class="o">+</span> <span class="n">expr2</span> <span class="o">*</span> <span class="p">(</span><span class="n">expr3</span> <span class="o">-</span> <span class="n">expr4</span><span class="p">)</span>
<span class="n">expr1</span><span class="p">(</span><span class="n">expr2</span><span class="p">,</span> <span class="n">expr3</span><span class="p">,</span> <span class="o">*</span><span class="n">expr4</span><span class="p">,</span> <span class="o">**</span><span class="n">expr5</span><span class="p">)</span>
<span class="n">expr3</span><span class="p">,</span> <span class="n">expr4</span> <span class="o">=</span> <span class="n">expr1</span><span class="p">,</span> <span class="n">expr2</span>
</pre></div>
</div>
</section>
<section id="operator-precedence">
<span id="operator-summary"></span><h2><span class="section-number">6.17. </span>Operator precedence<a class="headerlink" href="#operator-precedence" title="Link to this heading">¶</a></h2>
<p id="index-97">The following table summarizes the operator precedence in Python, from highest
precedence (most binding) to lowest precedence (least binding).  Operators in
the same box have the same precedence.  Unless the syntax is explicitly given,
operators are binary.  Operators in the same box group left to right (except for
exponentiation and conditional expressions, which group from right to left).</p>
<p>Note that comparisons, membership tests, and identity tests, all have the same
precedence and have a left-to-right chaining feature as described in the
<a class="reference internal" href="#comparisons"><span class="std std-ref">Comparisons</span></a> section.</p>
<table class="docutils align-default">
<thead>
<tr class="row-odd"><th class="head"><p>Operator</p></th>
<th class="head"><p>Description</p></th>
</tr>
</thead>
<tbody>
<tr class="row-even"><td><p><code class="docutils literal notranslate"><span class="pre">(expressions...)</span></code>,</p>
<p><code class="docutils literal notranslate"><span class="pre">[expressions...]</span></code>,
<code class="docutils literal notranslate"><span class="pre">{key:</span> <span class="pre">value...}</span></code>,
<code class="docutils literal notranslate"><span class="pre">{expressions...}</span></code></p>
</td>
<td><p>Binding or parenthesized
expression,
list display,
dictionary display,
set display</p></td>
</tr>
<tr class="row-odd"><td><p><code class="docutils literal notranslate"><span class="pre">x[index]</span></code>, <code class="docutils literal notranslate"><span class="pre">x[index:index]</span></code>
<code class="docutils literal notranslate"><span class="pre">x(arguments...)</span></code>, <code class="docutils literal notranslate"><span class="pre">x.attribute</span></code></p></td>
<td><p>Subscription (including slicing),
call, attribute reference</p></td>
</tr>
<tr class="row-even"><td><p><a class="reference internal" href="#await"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">await</span> <span class="pre">x</span></code></a></p></td>
<td><p>Await expression</p></td>
</tr>
<tr class="row-odd"><td><p><code class="docutils literal notranslate"><span class="pre">**</span></code></p></td>
<td><p>Exponentiation <a class="footnote-reference brackets" href="#id22" id="id16" role="doc-noteref"><span class="fn-bracket">[</span>5<span class="fn-bracket">]</span></a></p></td>
</tr>
<tr class="row-even"><td><p><code class="docutils literal notranslate"><span class="pre">+x</span></code>, <code class="docutils literal notranslate"><span class="pre">-x</span></code>, <code class="docutils literal notranslate"><span class="pre">~x</span></code></p></td>
<td><p>Positive, negative, bitwise NOT</p></td>
</tr>
<tr class="row-odd"><td><p><code class="docutils literal notranslate"><span class="pre">*</span></code>, <code class="docutils literal notranslate"><span class="pre">&#64;</span></code>, <code class="docutils literal notranslate"><span class="pre">/</span></code>, <code class="docutils literal notranslate"><span class="pre">//</span></code>, <code class="docutils literal notranslate"><span class="pre">%</span></code></p></td>
<td><p>Multiplication, matrix
multiplication, division, floor
division, remainder <a class="footnote-reference brackets" href="#id23" id="id17" role="doc-noteref"><span class="fn-bracket">[</span>6<span class="fn-bracket">]</span></a></p></td>
</tr>
<tr class="row-even"><td><p><code class="docutils literal notranslate"><span class="pre">+</span></code>, <code class="docutils literal notranslate"><span class="pre">-</span></code></p></td>
<td><p>Addition and subtraction</p></td>
</tr>
<tr class="row-odd"><td><p><code class="docutils literal notranslate"><span class="pre">&lt;&lt;</span></code>, <code class="docutils literal notranslate"><span class="pre">&gt;&gt;</span></code></p></td>
<td><p>Shifts</p></td>
</tr>
<tr class="row-even"><td><p><code class="docutils literal notranslate"><span class="pre">&amp;</span></code></p></td>
<td><p>Bitwise AND</p></td>
</tr>
<tr class="row-odd"><td><p><code class="docutils literal notranslate"><span class="pre">^</span></code></p></td>
<td><p>Bitwise XOR</p></td>
</tr>
<tr class="row-even"><td><p><code class="docutils literal notranslate"><span class="pre">|</span></code></p></td>
<td><p>Bitwise OR</p></td>
</tr>
<tr class="row-odd"><td><p><a class="reference internal" href="#in"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">in</span></code></a>, <a class="reference internal" href="#not-in"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">not</span> <span class="pre">in</span></code></a>,
<a class="reference internal" href="#is"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">is</span></code></a>, <a class="reference internal" href="#is-not"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">is</span> <span class="pre">not</span></code></a>, <code class="docutils literal notranslate"><span class="pre">&lt;</span></code>,
<code class="docutils literal notranslate"><span class="pre">&lt;=</span></code>, <code class="docutils literal notranslate"><span class="pre">&gt;</span></code>, <code class="docutils literal notranslate"><span class="pre">&gt;=</span></code>, <code class="docutils literal notranslate"><span class="pre">!=</span></code>, <code class="docutils literal notranslate"><span class="pre">==</span></code></p></td>
<td><p>Comparisons, including membership
tests and identity tests</p></td>
</tr>
<tr class="row-even"><td><p><a class="reference internal" href="#not"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">not</span> <span class="pre">x</span></code></a></p></td>
<td><p>Boolean NOT</p></td>
</tr>
<tr class="row-odd"><td><p><a class="reference internal" href="#and"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">and</span></code></a></p></td>
<td><p>Boolean AND</p></td>
</tr>
<tr class="row-even"><td><p><a class="reference internal" href="#or"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">or</span></code></a></p></td>
<td><p>Boolean OR</p></td>
</tr>
<tr class="row-odd"><td><p><a class="reference internal" href="#if-expr"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">if</span></code></a> – <code class="xref std std-keyword docutils literal notranslate"><span class="pre">else</span></code></p></td>
<td><p>Conditional expression</p></td>
</tr>
<tr class="row-even"><td><p><a class="reference internal" href="#lambda"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">lambda</span></code></a></p></td>
<td><p>Lambda expression</p></td>
</tr>
<tr class="row-odd"><td><p><code class="docutils literal notranslate"><span class="pre">:=</span></code></p></td>
<td><p>Assignment expression</p></td>
</tr>
</tbody>
</table>
<p class="rubric">Footnotes</p>
<aside class="footnote-list brackets">
<aside class="footnote brackets" id="id18" role="doc-footnote">
<span class="label"><span class="fn-bracket">[</span><a role="doc-backlink" href="#id9">1</a><span class="fn-bracket">]</span></span>
<p>While <code class="docutils literal notranslate"><span class="pre">abs(x%y)</span> <span class="pre">&lt;</span> <span class="pre">abs(y)</span></code> is true mathematically, for floats it may not be
true numerically due to roundoff.  For example, and assuming a platform on which
a Python float is an IEEE 754 double-precision number, in order that <code class="docutils literal notranslate"><span class="pre">-1e-100</span> <span class="pre">%</span>
<span class="pre">1e100</span></code> have the same sign as <code class="docutils literal notranslate"><span class="pre">1e100</span></code>, the computed result is <code class="docutils literal notranslate"><span class="pre">-1e-100</span> <span class="pre">+</span>
<span class="pre">1e100</span></code>, which is numerically exactly equal to <code class="docutils literal notranslate"><span class="pre">1e100</span></code>.  The function
<a class="reference internal" href="../library/math.html#math.fmod" title="math.fmod"><code class="xref py py-func docutils literal notranslate"><span class="pre">math.fmod()</span></code></a> returns a result whose sign matches the sign of the
first argument instead, and so returns <code class="docutils literal notranslate"><span class="pre">-1e-100</span></code> in this case. Which approach
is more appropriate depends on the application.</p>
</aside>
<aside class="footnote brackets" id="id19" role="doc-footnote">
<span class="label"><span class="fn-bracket">[</span><a role="doc-backlink" href="#id10">2</a><span class="fn-bracket">]</span></span>
<p>If x is very close to an exact integer multiple of y, it’s possible for
<code class="docutils literal notranslate"><span class="pre">x//y</span></code> to be one larger than <code class="docutils literal notranslate"><span class="pre">(x-x%y)//y</span></code> due to rounding.  In such
cases, Python returns the latter result, in order to preserve that
<code class="docutils literal notranslate"><span class="pre">divmod(x,y)[0]</span> <span class="pre">*</span> <span class="pre">y</span> <span class="pre">+</span> <span class="pre">x</span> <span class="pre">%</span> <span class="pre">y</span></code> be very close to <code class="docutils literal notranslate"><span class="pre">x</span></code>.</p>
</aside>
<aside class="footnote brackets" id="id20" role="doc-footnote">
<span class="label"><span class="fn-bracket">[</span><a role="doc-backlink" href="#id12">3</a><span class="fn-bracket">]</span></span>
<p>The Unicode standard distinguishes between <em class="dfn">code points</em>
(e.g. U+0041) and <em class="dfn">abstract characters</em> (e.g. “LATIN CAPITAL LETTER A”).
While most abstract characters in Unicode are only represented using one
code point, there is a number of abstract characters that can in addition be
represented using a sequence of more than one code point.  For example, the
abstract character “LATIN CAPITAL LETTER C WITH CEDILLA” can be represented
as a single <em class="dfn">precomposed character</em> at code position U+00C7, or as a
sequence of a <em class="dfn">base character</em> at code position U+0043 (LATIN CAPITAL
LETTER C), followed by a <em class="dfn">combining character</em> at code position U+0327
(COMBINING CEDILLA).</p>
<p>The comparison operators on strings compare at the level of Unicode code
points. This may be counter-intuitive to humans.  For example,
<code class="docutils literal notranslate"><span class="pre">&quot;\u00C7&quot;</span> <span class="pre">==</span> <span class="pre">&quot;\u0043\u0327&quot;</span></code> is <code class="docutils literal notranslate"><span class="pre">False</span></code>, even though both strings
represent the same abstract character “LATIN CAPITAL LETTER C WITH CEDILLA”.</p>
<p>To compare strings at the level of abstract characters (that is, in a way
intuitive to humans), use <a class="reference internal" href="../library/unicodedata.html#unicodedata.normalize" title="unicodedata.normalize"><code class="xref py py-func docutils literal notranslate"><span class="pre">unicodedata.normalize()</span></code></a>.</p>
</aside>
<aside class="footnote brackets" id="id21" role="doc-footnote">
<span class="label"><span class="fn-bracket">[</span><a role="doc-backlink" href="#id13">4</a><span class="fn-bracket">]</span></span>
<p>Due to automatic garbage-collection, free lists, and the dynamic nature of
descriptors, you may notice seemingly unusual behaviour in certain uses of
the <a class="reference internal" href="#is"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">is</span></code></a> operator, like those involving comparisons between instance
methods, or constants.  Check their documentation for more info.</p>
</aside>
<aside class="footnote brackets" id="id22" role="doc-footnote">
<span class="label"><span class="fn-bracket">[</span><a role="doc-backlink" href="#id16">5</a><span class="fn-bracket">]</span></span>
<p>The power operator <code class="docutils literal notranslate"><span class="pre">**</span></code> binds less tightly than an arithmetic or
bitwise unary operator on its right, that is, <code class="docutils literal notranslate"><span class="pre">2**-1</span></code> is <code class="docutils literal notranslate"><span class="pre">0.5</span></code>.</p>
</aside>
<aside class="footnote brackets" id="id23" role="doc-footnote">
<span class="label"><span class="fn-bracket">[</span><a role="doc-backlink" href="#id17">6</a><span class="fn-bracket">]</span></span>
<p>The <code class="docutils literal notranslate"><span class="pre">%</span></code> operator is also used for string formatting; the same
precedence applies.</p>
</aside>
</aside>
</section>
</section>


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    <h3><a href="../contents.html">Table of Contents</a></h3>
    <ul>
<li><a class="reference internal" href="#">6. Expressions</a><ul>
<li><a class="reference internal" href="#arithmetic-conversions">6.1. Arithmetic conversions</a></li>
<li><a class="reference internal" href="#atoms">6.2. Atoms</a><ul>
<li><a class="reference internal" href="#built-in-constants">6.2.1. Built-in constants</a></li>
<li><a class="reference internal" href="#atom-identifiers">6.2.2. Identifiers (Names)</a><ul>
<li><a class="reference internal" href="#index-5">6.2.2.1. Private name mangling</a></li>
</ul>
</li>
<li><a class="reference internal" href="#literals">6.2.3. Literals</a><ul>
<li><a class="reference internal" href="#literals-and-object-identity">6.2.3.1. Literals and object identity</a></li>
<li><a class="reference internal" href="#string-literal-concatenation">6.2.3.2. String literal concatenation</a></li>
</ul>
</li>
<li><a class="reference internal" href="#parenthesized-forms">6.2.4. Parenthesized forms</a></li>
<li><a class="reference internal" href="#displays-for-lists-sets-and-dictionaries">6.2.5. Displays for lists, sets and dictionaries</a></li>
<li><a class="reference internal" href="#list-displays">6.2.6. List displays</a></li>
<li><a class="reference internal" href="#set-displays">6.2.7. Set displays</a></li>
<li><a class="reference internal" href="#dictionary-displays">6.2.8. Dictionary displays</a></li>
<li><a class="reference internal" href="#generator-expressions">6.2.9. Generator expressions</a></li>
<li><a class="reference internal" href="#yield-expressions">6.2.10. Yield expressions</a><ul>
<li><a class="reference internal" href="#generator-iterator-methods">6.2.10.1. Generator-iterator methods</a></li>
<li><a class="reference internal" href="#examples">6.2.10.2. Examples</a></li>
<li><a class="reference internal" href="#asynchronous-generator-functions">6.2.10.3. Asynchronous generator functions</a></li>
<li><a class="reference internal" href="#asynchronous-generator-iterator-methods">6.2.10.4. Asynchronous generator-iterator methods</a></li>
</ul>
</li>
</ul>
</li>
<li><a class="reference internal" href="#primaries">6.3. Primaries</a><ul>
<li><a class="reference internal" href="#attribute-references">6.3.1. Attribute references</a></li>
<li><a class="reference internal" href="#subscriptions-and-slicings">6.3.2. Subscriptions and slicings</a><ul>
<li><a class="reference internal" href="#slicings">6.3.2.1. Slicings</a></li>
<li><a class="reference internal" href="#comma-separated-subscripts">6.3.2.2. Comma-separated subscripts</a></li>
<li><a class="reference internal" href="#starred-subscriptions">6.3.2.3. “Starred” subscriptions</a></li>
<li><a class="reference internal" href="#formal-subscription-grammar">6.3.2.4. Formal subscription grammar</a></li>
</ul>
</li>
<li><a class="reference internal" href="#calls">6.3.3. Calls</a></li>
</ul>
</li>
<li><a class="reference internal" href="#await-expression">6.4. Await expression</a></li>
<li><a class="reference internal" href="#the-power-operator">6.5. The power operator</a></li>
<li><a class="reference internal" href="#unary-arithmetic-and-bitwise-operations">6.6. Unary arithmetic and bitwise operations</a></li>
<li><a class="reference internal" href="#binary-arithmetic-operations">6.7. Binary arithmetic operations</a></li>
<li><a class="reference internal" href="#shifting-operations">6.8. Shifting operations</a></li>
<li><a class="reference internal" href="#binary-bitwise-operations">6.9. Binary bitwise operations</a></li>
<li><a class="reference internal" href="#comparisons">6.10. Comparisons</a><ul>
<li><a class="reference internal" href="#value-comparisons">6.10.1. Value comparisons</a></li>
<li><a class="reference internal" href="#membership-test-operations">6.10.2. Membership test operations</a></li>
<li><a class="reference internal" href="#is-not">6.10.3. Identity comparisons</a></li>
</ul>
</li>
<li><a class="reference internal" href="#boolean-operations">6.11. Boolean operations</a></li>
<li><a class="reference internal" href="#assignment-expressions">6.12. Assignment expressions</a></li>
<li><a class="reference internal" href="#conditional-expressions">6.13. Conditional expressions</a></li>
<li><a class="reference internal" href="#lambda">6.14. Lambdas</a></li>
<li><a class="reference internal" href="#expression-lists">6.15. Expression lists</a></li>
<li><a class="reference internal" href="#evaluation-order">6.16. Evaluation order</a></li>
<li><a class="reference internal" href="#operator-precedence">6.17. Operator precedence</a></li>
</ul>
</li>
</ul>

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