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  <section id="pyhash-api">
<h1>PyHash API<a class="headerlink" href="#pyhash-api" title="Link to this heading">¶</a></h1>
<p>See also the <a class="reference internal" href="typeobj.html#c.PyTypeObject.tp_hash" title="PyTypeObject.tp_hash"><code class="xref c c-member docutils literal notranslate"><span class="pre">PyTypeObject.tp_hash</span></code></a> member and <a class="reference internal" href="../library/stdtypes.html#numeric-hash"><span class="std std-ref">Hashing of numeric types</span></a>.</p>
<dl class="c type">
<dt class="sig sig-object c" id="c.Py_hash_t">
<span class="k"><span class="pre">type</span></span><span class="w"> </span><span class="sig-name descname"><span class="n"><span class="pre">Py_hash_t</span></span></span><a class="headerlink" href="#c.Py_hash_t" title="Link to this definition">¶</a><br /></dt>
<dd><p>Hash value type: signed integer.</p>
<div class="versionadded">
<p><span class="versionmodified added">Added in version 3.2.</span></p>
</div>
</dd></dl>

<dl class="c type">
<dt class="sig sig-object c" id="c.Py_uhash_t">
<span class="k"><span class="pre">type</span></span><span class="w"> </span><span class="sig-name descname"><span class="n"><span class="pre">Py_uhash_t</span></span></span><a class="headerlink" href="#c.Py_uhash_t" title="Link to this definition">¶</a><br /></dt>
<dd><p>Hash value type: unsigned integer.</p>
<div class="versionadded">
<p><span class="versionmodified added">Added in version 3.2.</span></p>
</div>
</dd></dl>

<dl class="c macro">
<dt class="sig sig-object c" id="c.Py_HASH_ALGORITHM">
<span class="sig-name descname"><span class="n"><span class="pre">Py_HASH_ALGORITHM</span></span></span><a class="headerlink" href="#c.Py_HASH_ALGORITHM" title="Link to this definition">¶</a><br /></dt>
<dd><p>A numerical value indicating the algorithm for hashing 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>,
<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>, and <a class="reference internal" href="../library/stdtypes.html#memoryview" title="memoryview"><code class="xref py py-class docutils literal notranslate"><span class="pre">memoryview</span></code></a>.</p>
<p>The algorithm name is exposed by <a class="reference internal" href="../library/sys.html#sys.hash_info.algorithm" title="sys.hash_info.algorithm"><code class="xref py py-data docutils literal notranslate"><span class="pre">sys.hash_info.algorithm</span></code></a>.</p>
<div class="versionadded">
<p><span class="versionmodified added">Added in version 3.4.</span></p>
</div>
</dd></dl>

<dl class="c macro">
<dt class="sig sig-object c" id="c.Py_HASH_FNV">
<span class="sig-name descname"><span class="n"><span class="pre">Py_HASH_FNV</span></span></span><a class="headerlink" href="#c.Py_HASH_FNV" title="Link to this definition">¶</a><br /></dt>
<dt class="sig sig-object c" id="c.Py_HASH_SIPHASH24">
<span class="sig-name descname"><span class="n"><span class="pre">Py_HASH_SIPHASH24</span></span></span><a class="headerlink" href="#c.Py_HASH_SIPHASH24" title="Link to this definition">¶</a><br /></dt>
<dt class="sig sig-object c" id="c.Py_HASH_SIPHASH13">
<span class="sig-name descname"><span class="n"><span class="pre">Py_HASH_SIPHASH13</span></span></span><a class="headerlink" href="#c.Py_HASH_SIPHASH13" title="Link to this definition">¶</a><br /></dt>
<dd><p>Numerical values to compare to <a class="reference internal" href="#c.Py_HASH_ALGORITHM" title="Py_HASH_ALGORITHM"><code class="xref c c-macro docutils literal notranslate"><span class="pre">Py_HASH_ALGORITHM</span></code></a> to determine
which algorithm is used for hashing. The hash algorithm can be configured
via the configure <a class="reference internal" href="../using/configure.html#cmdoption-with-hash-algorithm"><code class="xref std std-option docutils literal notranslate"><span class="pre">--with-hash-algorithm</span></code></a> option.</p>
<div class="versionadded">
<p><span class="versionmodified added">Added in version 3.4: </span>Add <code class="xref c c-macro docutils literal notranslate"><span class="pre">Py_HASH_FNV</span></code> and <code class="xref c c-macro docutils literal notranslate"><span class="pre">Py_HASH_SIPHASH24</span></code>.</p>
</div>
<div class="versionadded">
<p><span class="versionmodified added">Added in version 3.11: </span>Add <code class="xref c c-macro docutils literal notranslate"><span class="pre">Py_HASH_SIPHASH13</span></code>.</p>
</div>
</dd></dl>

<dl class="c macro">
<dt class="sig sig-object c" id="c.Py_HASH_CUTOFF">
<span class="sig-name descname"><span class="n"><span class="pre">Py_HASH_CUTOFF</span></span></span><a class="headerlink" href="#c.Py_HASH_CUTOFF" title="Link to this definition">¶</a><br /></dt>
<dd><p>Buffers of length in range <code class="docutils literal notranslate"><span class="pre">[1,</span> <span class="pre">Py_HASH_CUTOFF)</span></code> are hashed using DJBX33A
instead of the algorithm described by <a class="reference internal" href="#c.Py_HASH_ALGORITHM" title="Py_HASH_ALGORITHM"><code class="xref c c-macro docutils literal notranslate"><span class="pre">Py_HASH_ALGORITHM</span></code></a>.</p>
<ul class="simple">
<li><p>A <code class="xref c c-macro docutils literal notranslate"><span class="pre">Py_HASH_CUTOFF</span></code> of 0 disables the optimization.</p></li>
<li><p><code class="xref c c-macro docutils literal notranslate"><span class="pre">Py_HASH_CUTOFF</span></code> must be non-negative and less or equal than 7.</p></li>
</ul>
<p>32-bit platforms should use a cutoff smaller than 64-bit platforms because
it is easier to create colliding strings. A cutoff of 7 on 64-bit platforms
and 5 on 32-bit platforms should provide a decent safety margin.</p>
<p>This corresponds to the <a class="reference internal" href="../library/sys.html#sys.hash_info.cutoff" title="sys.hash_info.cutoff"><code class="xref py py-data docutils literal notranslate"><span class="pre">sys.hash_info.cutoff</span></code></a> constant.</p>
<div class="versionadded">
<p><span class="versionmodified added">Added in version 3.4.</span></p>
</div>
</dd></dl>

<dl class="c macro">
<dt class="sig sig-object c" id="c.PyHASH_MODULUS">
<span class="sig-name descname"><span class="n"><span class="pre">PyHASH_MODULUS</span></span></span><a class="headerlink" href="#c.PyHASH_MODULUS" title="Link to this definition">¶</a><br /></dt>
<dd><p>The <a class="reference external" href="https://en.wikipedia.org/wiki/Mersenne_prime">Mersenne prime</a> <code class="docutils literal notranslate"><span class="pre">P</span> <span class="pre">=</span> <span class="pre">2**n</span> <span class="pre">-1</span></code>,
used for numeric hash scheme.</p>
<p>This corresponds to the <a class="reference internal" href="../library/sys.html#sys.hash_info.modulus" title="sys.hash_info.modulus"><code class="xref py py-data docutils literal notranslate"><span class="pre">sys.hash_info.modulus</span></code></a> constant.</p>
<div class="versionadded">
<p><span class="versionmodified added">Added in version 3.13.</span></p>
</div>
</dd></dl>

<dl class="c macro">
<dt class="sig sig-object c" id="c.PyHASH_BITS">
<span class="sig-name descname"><span class="n"><span class="pre">PyHASH_BITS</span></span></span><a class="headerlink" href="#c.PyHASH_BITS" title="Link to this definition">¶</a><br /></dt>
<dd><p>The exponent <code class="docutils literal notranslate"><span class="pre">n</span></code> of <code class="docutils literal notranslate"><span class="pre">P</span></code> in <a class="reference internal" href="#c.PyHASH_MODULUS" title="PyHASH_MODULUS"><code class="xref c c-macro docutils literal notranslate"><span class="pre">PyHASH_MODULUS</span></code></a>.</p>
<div class="versionadded">
<p><span class="versionmodified added">Added in version 3.13.</span></p>
</div>
</dd></dl>

<dl class="c macro">
<dt class="sig sig-object c" id="c.PyHASH_MULTIPLIER">
<span class="sig-name descname"><span class="n"><span class="pre">PyHASH_MULTIPLIER</span></span></span><a class="headerlink" href="#c.PyHASH_MULTIPLIER" title="Link to this definition">¶</a><br /></dt>
<dd><p>Prime multiplier used in string and various other hashes.</p>
<div class="versionadded">
<p><span class="versionmodified added">Added in version 3.13.</span></p>
</div>
</dd></dl>

<dl class="c macro">
<dt class="sig sig-object c" id="c.PyHASH_INF">
<span class="sig-name descname"><span class="n"><span class="pre">PyHASH_INF</span></span></span><a class="headerlink" href="#c.PyHASH_INF" title="Link to this definition">¶</a><br /></dt>
<dd><p>The hash value returned for a positive infinity.</p>
<p>This corresponds to the <a class="reference internal" href="../library/sys.html#sys.hash_info.inf" title="sys.hash_info.inf"><code class="xref py py-data docutils literal notranslate"><span class="pre">sys.hash_info.inf</span></code></a> constant.</p>
<div class="versionadded">
<p><span class="versionmodified added">Added in version 3.13.</span></p>
</div>
</dd></dl>

<dl class="c macro">
<dt class="sig sig-object c" id="c.PyHASH_IMAG">
<span class="sig-name descname"><span class="n"><span class="pre">PyHASH_IMAG</span></span></span><a class="headerlink" href="#c.PyHASH_IMAG" title="Link to this definition">¶</a><br /></dt>
<dd><p>The multiplier used for the imaginary part of a complex number.</p>
<p>This corresponds to the <a class="reference internal" href="../library/sys.html#sys.hash_info.imag" title="sys.hash_info.imag"><code class="xref py py-data docutils literal notranslate"><span class="pre">sys.hash_info.imag</span></code></a> constant.</p>
<div class="versionadded">
<p><span class="versionmodified added">Added in version 3.13.</span></p>
</div>
</dd></dl>

<dl class="c type">
<dt class="sig sig-object c" id="c.PyHash_FuncDef">
<span class="k"><span class="pre">type</span></span><span class="w"> </span><span class="sig-name descname"><span class="n"><span class="pre">PyHash_FuncDef</span></span></span><a class="headerlink" href="#c.PyHash_FuncDef" title="Link to this definition">¶</a><br /></dt>
<dd><p>Hash function definition used by <a class="reference internal" href="#c.PyHash_GetFuncDef" title="PyHash_GetFuncDef"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyHash_GetFuncDef()</span></code></a>.</p>
<dl class="c member">
<dt class="sig sig-object c" id="c.PyHash_FuncDef.hash">
<a class="reference internal" href="#c.Py_hash_t" title="Py_hash_t"><span class="n"><span class="pre">Py_hash_t</span></span></a><span class="w"> </span><span class="p"><span class="pre">(</span></span><span class="p"><span class="pre">*</span></span><span class="k"><span class="pre">const</span></span><span class="w"> </span><span class="sig-name descname"><span class="n"><span class="pre">hash</span></span></span><span class="p"><span class="pre">)</span></span><span class="p"><span class="pre">(</span></span><span class="k"><span class="pre">const</span></span><span class="w"> </span><span class="kt"><span class="pre">void</span></span><span class="p"><span class="pre">*</span></span><span class="p"><span class="pre">,</span></span><span class="w"> </span><a class="reference internal" href="intro.html#c.Py_ssize_t" title="Py_ssize_t"><span class="n"><span class="pre">Py_ssize_t</span></span></a><span class="p"><span class="pre">)</span></span><a class="headerlink" href="#c.PyHash_FuncDef.hash" title="Link to this definition">¶</a><br /></dt>
<dd><p>Hash function.</p>
</dd></dl>

<dl class="c member">
<dt class="sig sig-object c" id="c.PyHash_FuncDef.name">
<span class="k"><span class="pre">const</span></span><span class="w"> </span><span class="kt"><span class="pre">char</span></span><span class="w"> </span><span class="p"><span class="pre">*</span></span><span class="sig-name descname"><span class="n"><span class="pre">name</span></span></span><a class="headerlink" href="#c.PyHash_FuncDef.name" title="Link to this definition">¶</a><br /></dt>
<dd><p>Hash function name (UTF-8 encoded string).</p>
<p>This corresponds to the <a class="reference internal" href="../library/sys.html#sys.hash_info.algorithm" title="sys.hash_info.algorithm"><code class="xref py py-data docutils literal notranslate"><span class="pre">sys.hash_info.algorithm</span></code></a> constant.</p>
</dd></dl>

<dl class="c member">
<dt class="sig sig-object c" id="c.PyHash_FuncDef.hash_bits">
<span class="k"><span class="pre">const</span></span><span class="w"> </span><span class="kt"><span class="pre">int</span></span><span class="w"> </span><span class="sig-name descname"><span class="n"><span class="pre">hash_bits</span></span></span><a class="headerlink" href="#c.PyHash_FuncDef.hash_bits" title="Link to this definition">¶</a><br /></dt>
<dd><p>Internal size of the hash value in bits.</p>
<p>This corresponds to the <a class="reference internal" href="../library/sys.html#sys.hash_info.hash_bits" title="sys.hash_info.hash_bits"><code class="xref py py-data docutils literal notranslate"><span class="pre">sys.hash_info.hash_bits</span></code></a> constant.</p>
</dd></dl>

<dl class="c member">
<dt class="sig sig-object c" id="c.PyHash_FuncDef.seed_bits">
<span class="k"><span class="pre">const</span></span><span class="w"> </span><span class="kt"><span class="pre">int</span></span><span class="w"> </span><span class="sig-name descname"><span class="n"><span class="pre">seed_bits</span></span></span><a class="headerlink" href="#c.PyHash_FuncDef.seed_bits" title="Link to this definition">¶</a><br /></dt>
<dd><p>Size of seed input in bits.</p>
<p>This corresponds to the <a class="reference internal" href="../library/sys.html#sys.hash_info.seed_bits" title="sys.hash_info.seed_bits"><code class="xref py py-data docutils literal notranslate"><span class="pre">sys.hash_info.seed_bits</span></code></a> constant.</p>
</dd></dl>

<div class="versionadded">
<p><span class="versionmodified added">Added in version 3.4.</span></p>
</div>
</dd></dl>

<dl class="c function">
<dt class="sig sig-object c" id="c.PyHash_GetFuncDef">
<a class="reference internal" href="#c.PyHash_FuncDef" title="PyHash_FuncDef"><span class="n"><span class="pre">PyHash_FuncDef</span></span></a><span class="w"> </span><span class="p"><span class="pre">*</span></span><span class="sig-name descname"><span class="n"><span class="pre">PyHash_GetFuncDef</span></span></span><span class="sig-paren">(</span><span class="kt"><span class="pre">void</span></span><span class="sig-paren">)</span><a class="headerlink" href="#c.PyHash_GetFuncDef" title="Link to this definition">¶</a><br /></dt>
<dd><p>Get the hash function definition.</p>
<div class="admonition seealso">
<p class="admonition-title">See also</p>
<p><span class="target" id="index-0"></span><a class="pep reference external" href="https://peps.python.org/pep-0456/"><strong>PEP 456</strong></a> “Secure and interchangeable hash algorithm”.</p>
</div>
<div class="versionadded">
<p><span class="versionmodified added">Added in version 3.4.</span></p>
</div>
</dd></dl>

<dl class="c function">
<dt class="sig sig-object c" id="c.Py_HashPointer">
<a class="reference internal" href="#c.Py_hash_t" title="Py_hash_t"><span class="n"><span class="pre">Py_hash_t</span></span></a><span class="w"> </span><span class="sig-name descname"><span class="n"><span class="pre">Py_HashPointer</span></span></span><span class="sig-paren">(</span><span class="k"><span class="pre">const</span></span><span class="w"> </span><span class="kt"><span class="pre">void</span></span><span class="w"> </span><span class="p"><span class="pre">*</span></span><span class="n"><span class="pre">ptr</span></span><span class="sig-paren">)</span><a class="headerlink" href="#c.Py_HashPointer" title="Link to this definition">¶</a><br /></dt>
<dd><p>Hash a pointer value: process the pointer value as an integer (cast it to
<code class="docutils literal notranslate"><span class="pre">uintptr_t</span></code> internally). The pointer is not dereferenced.</p>
<p>The function cannot fail: it cannot return <code class="docutils literal notranslate"><span class="pre">-1</span></code>.</p>
<div class="versionadded">
<p><span class="versionmodified added">Added in version 3.13.</span></p>
</div>
</dd></dl>

<dl class="c function">
<dt class="sig sig-object c" id="c.Py_HashBuffer">
<a class="reference internal" href="#c.Py_hash_t" title="Py_hash_t"><span class="n"><span class="pre">Py_hash_t</span></span></a><span class="w"> </span><span class="sig-name descname"><span class="n"><span class="pre">Py_HashBuffer</span></span></span><span class="sig-paren">(</span><span class="k"><span class="pre">const</span></span><span class="w"> </span><span class="kt"><span class="pre">void</span></span><span class="w"> </span><span class="p"><span class="pre">*</span></span><span class="n"><span class="pre">ptr</span></span>, <a class="reference internal" href="intro.html#c.Py_ssize_t" title="Py_ssize_t"><span class="n"><span class="pre">Py_ssize_t</span></span></a><span class="w"> </span><span class="n"><span class="pre">len</span></span><span class="sig-paren">)</span><a class="headerlink" href="#c.Py_HashBuffer" title="Link to this definition">¶</a><br /></dt>
<dd><p>Compute and return the hash value of a buffer of <em>len</em> bytes
starting at address <em>ptr</em>. The hash is guaranteed to match that 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>, <a class="reference internal" href="../library/stdtypes.html#memoryview" title="memoryview"><code class="xref py py-class docutils literal notranslate"><span class="pre">memoryview</span></code></a>, and other built-in objects
that implement the <a class="reference internal" href="buffer.html#bufferobjects"><span class="std std-ref">buffer protocol</span></a>.</p>
<p>Use this function to implement hashing for immutable objects whose
<a class="reference internal" href="typeobj.html#c.PyTypeObject.tp_richcompare" title="PyTypeObject.tp_richcompare"><code class="xref c c-member docutils literal notranslate"><span class="pre">tp_richcompare</span></code></a> function compares to another
object’s buffer.</p>
<p><em>len</em> must be greater than or equal to <code class="docutils literal notranslate"><span class="pre">0</span></code>.</p>
<p>This function always succeeds.</p>
<div class="versionadded">
<p><span class="versionmodified added">Added in version 3.14.</span></p>
</div>
</dd></dl>

<dl class="c function">
<dt class="sig sig-object c" id="c.PyObject_GenericHash">
<a class="reference internal" href="#c.Py_hash_t" title="Py_hash_t"><span class="n"><span class="pre">Py_hash_t</span></span></a><span class="w"> </span><span class="sig-name descname"><span class="n"><span class="pre">PyObject_GenericHash</span></span></span><span class="sig-paren">(</span><a class="reference internal" href="structures.html#c.PyObject" title="PyObject"><span class="n"><span class="pre">PyObject</span></span></a><span class="w"> </span><span class="p"><span class="pre">*</span></span><span class="n"><span class="pre">obj</span></span><span class="sig-paren">)</span><a class="headerlink" href="#c.PyObject_GenericHash" title="Link to this definition">¶</a><br /></dt>
<dd><p>Generic hashing function that is meant to be put into a type
object’s <code class="docutils literal notranslate"><span class="pre">tp_hash</span></code> slot.
Its result only depends on the object’s identity.</p>
<div class="impl-detail compound">
<p><strong>CPython implementation detail:</strong> In CPython, it is equivalent to <a class="reference internal" href="#c.Py_HashPointer" title="Py_HashPointer"><code class="xref c c-func docutils literal notranslate"><span class="pre">Py_HashPointer()</span></code></a>.</p>
</div>
<div class="versionadded">
<p><span class="versionmodified added">Added in version 3.13.</span></p>
</div>
</dd></dl>

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