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Doc/library/configparser.rst
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Erlend E. Aasland
[3.11] Docs: align usage of versionadded/versionchanged with recommended practice (#114409) (#114473)
23 янв 2024, 12:39
23 янв 2024, 12:39eb94a04
:mod:`configparser` --- Configuration file parser
=================================================

.. module:: configparser
   :synopsis: Configuration file parser.

.. moduleauthor:: Ken Manheimer <klm@zope.com>
.. moduleauthor:: Barry Warsaw <bwarsaw@python.org>
.. moduleauthor:: Eric S. Raymond <esr@thyrsus.com>
.. moduleauthor:: Łukasz Langa <lukasz@langa.pl>
.. sectionauthor:: Christopher G. Petrilli <petrilli@amber.org>
.. sectionauthor:: Łukasz Langa <lukasz@langa.pl>

**Source code:** :source:`Lib/configparser.py`

.. index::
   pair: .ini; file
   pair: configuration; file
   single: ini file
   single: Windows ini file

--------------

This module provides the :class:`ConfigParser` class which implements a basic
configuration language which provides a structure similar to what's found in
Microsoft Windows INI files.  You can use this to write Python programs which
can be customized by end users easily.

.. note::

   This library does *not* interpret or write the value-type prefixes used in
   the Windows Registry extended version of INI syntax.

.. seealso::

   Module :mod:`tomllib`
      TOML is a well-specified format for application configuration files.
      It is specifically designed to be an improved version of INI.

   Module :mod:`shlex`
      Support for creating Unix shell-like mini-languages which can also
      be used for application configuration files.

   Module :mod:`json`
      The ``json`` module implements a subset of JavaScript syntax which is
      sometimes used for configuration, but does not support comments.


.. testsetup::

   import configparser

.. testcleanup::

   import os
   os.remove("example.ini")


Quick Start
-----------

Let's take a very basic configuration file that looks like this:

.. code-block:: ini

   [DEFAULT]
   ServerAliveInterval = 45
   Compression = yes
   CompressionLevel = 9
   ForwardX11 = yes

   [forge.example]
   User = hg

   [topsecret.server.example]
   Port = 50022
   ForwardX11 = no

The structure of INI files is described `in the following section
<#supported-ini-file-structure>`_.  Essentially, the file
consists of sections, each of which contains keys with values.
:mod:`configparser` classes can read and write such files.  Let's start by
creating the above configuration file programmatically.

.. doctest::

   >>> import configparser
   >>> config = configparser.ConfigParser()
   >>> config['DEFAULT'] = {'ServerAliveInterval': '45',
   ...                      'Compression': 'yes',
   ...                      'CompressionLevel': '9'}
   >>> config['forge.example'] = {}
   >>> config['forge.example']['User'] = 'hg'
   >>> config['topsecret.server.example'] = {}
   >>> topsecret = config['topsecret.server.example']
   >>> topsecret['Port'] = '50022'     # mutates the parser
   >>> topsecret['ForwardX11'] = 'no'  # same here
   >>> config['DEFAULT']['ForwardX11'] = 'yes'
   >>> with open('example.ini', 'w') as configfile:
   ...   config.write(configfile)
   ...

As you can see, we can treat a config parser much like a dictionary.
There are differences, `outlined later <#mapping-protocol-access>`_, but
the behavior is very close to what you would expect from a dictionary.

Now that we have created and saved a configuration file, let's read it
back and explore the data it holds.

.. doctest::

   >>> config = configparser.ConfigParser()
   >>> config.sections()
   []
   >>> config.read('example.ini')
   ['example.ini']
   >>> config.sections()
   ['forge.example', 'topsecret.server.example']
   >>> 'forge.example' in config
   True
   >>> 'python.org' in config
   False
   >>> config['forge.example']['User']
   'hg'
   >>> config['DEFAULT']['Compression']
   'yes'
   >>> topsecret = config['topsecret.server.example']
   >>> topsecret['ForwardX11']
   'no'
   >>> topsecret['Port']
   '50022'
   >>> for key in config['forge.example']:  # doctest: +SKIP
   ...     print(key)
   user
   compressionlevel
   serveraliveinterval
   compression
   forwardx11
   >>> config['forge.example']['ForwardX11']
   'yes'

As we can see above, the API is pretty straightforward.  The only bit of magic
involves the ``DEFAULT`` section which provides default values for all other
sections [1]_.  Note also that keys in sections are
case-insensitive and stored in lowercase [1]_.

It is possible to read several configurations into a single
:class:`ConfigParser`, where the most recently added configuration has the
highest priority. Any conflicting keys are taken from the more recent
configuration while the previously existing keys are retained.

.. doctest::

   >>> another_config = configparser.ConfigParser()
   >>> another_config.read('example.ini')
   ['example.ini']
   >>> another_config['topsecret.server.example']['Port']
   '50022'
   >>> another_config.read_string("[topsecret.server.example]\nPort=48484")
   >>> another_config['topsecret.server.example']['Port']
   '48484'
   >>> another_config.read_dict({"topsecret.server.example": {"Port": 21212}})
   >>> another_config['topsecret.server.example']['Port']
   '21212'
   >>> another_config['topsecret.server.example']['ForwardX11']
   'no'

This behaviour is equivalent to a :meth:`ConfigParser.read` call with several
files passed to the *filenames* parameter.


Supported Datatypes
-------------------

Config parsers do not guess datatypes of values in configuration files, always
storing them internally as strings.  This means that if you need other
datatypes, you should convert on your own:

.. doctest::

   >>> int(topsecret['Port'])
   50022
   >>> float(topsecret['CompressionLevel'])
   9.0

Since this task is so common, config parsers provide a range of handy getter
methods to handle integers, floats and booleans.  The last one is the most
interesting because simply passing the value to ``bool()`` would do no good
since ``bool('False')`` is still ``True``.  This is why config parsers also
provide :meth:`~ConfigParser.getboolean`.  This method is case-insensitive and
recognizes Boolean values from ``'yes'``/``'no'``, ``'on'``/``'off'``,
``'true'``/``'false'`` and ``'1'``/``'0'`` [1]_.  For example:

.. doctest::

   >>> topsecret.getboolean('ForwardX11')
   False
   >>> config['forge.example'].getboolean('ForwardX11')
   True
   >>> config.getboolean('forge.example', 'Compression')
   True

Apart from :meth:`~ConfigParser.getboolean`, config parsers also
provide equivalent :meth:`~ConfigParser.getint` and
:meth:`~ConfigParser.getfloat` methods.  You can register your own
converters and customize the provided ones. [1]_

Fallback Values
---------------

As with a dictionary, you can use a section's :meth:`~ConfigParser.get` method to
provide fallback values:

.. doctest::

   >>> topsecret.get('Port')
   '50022'
   >>> topsecret.get('CompressionLevel')
   '9'
   >>> topsecret.get('Cipher')
   >>> topsecret.get('Cipher', '3des-cbc')
   '3des-cbc'

Please note that default values have precedence over fallback values.
For instance, in our example the ``'CompressionLevel'`` key was
specified only in the ``'DEFAULT'`` section.  If we try to get it from
the section ``'topsecret.server.example'``, we will always get the default,
even if we specify a fallback:

.. doctest::

   >>> topsecret.get('CompressionLevel', '3')
   '9'

One more thing to be aware of is that the parser-level :meth:`~ConfigParser.get` method
provides a custom, more complex interface, maintained for backwards
compatibility.  When using this method, a fallback value can be provided via
the ``fallback`` keyword-only argument:

.. doctest::

   >>> config.get('forge.example', 'monster',
   ...            fallback='No such things as monsters')
   'No such things as monsters'

The same ``fallback`` argument can be used with the
:meth:`~ConfigParser.getint`, :meth:`~ConfigParser.getfloat` and
:meth:`~ConfigParser.getboolean` methods, for example:

.. doctest::

   >>> 'BatchMode' in topsecret
   False
   >>> topsecret.getboolean('BatchMode', fallback=True)
   True
   >>> config['DEFAULT']['BatchMode'] = 'no'
   >>> topsecret.getboolean('BatchMode', fallback=True)
   False


Supported INI File Structure
----------------------------

A configuration file consists of sections, each led by a ``[section]`` header,
followed by key/value entries separated by a specific string (``=`` or ``:`` by
default [1]_).  By default, section names are case sensitive but keys are not
[1]_.  Leading and trailing whitespace is removed from keys and values.
Values can be omitted if the parser is configured to allow it [1]_,
in which case the key/value delimiter may also be left
out.  Values can also span multiple lines, as long as they are indented deeper
than the first line of the value.  Depending on the parser's mode, blank lines
may be treated as parts of multiline values or ignored.

By default, a valid section name can be any string that does not contain '\\n'.
To change this, see :attr:`ConfigParser.SECTCRE`.

Configuration files may include comments, prefixed by specific
characters (``#`` and ``;`` by default [1]_).  Comments may appear on
their own on an otherwise empty line, possibly indented. [1]_

For example:

.. code-block:: ini

   [Simple Values]
   key=value
   spaces in keys=allowed
   spaces in values=allowed as well
   spaces around the delimiter = obviously
   you can also use : to delimit keys from values

   [All Values Are Strings]
   values like this: 1000000
   or this: 3.14159265359
   are they treated as numbers? : no
   integers, floats and booleans are held as: strings
   can use the API to get converted values directly: true

   [Multiline Values]
   chorus: I'm a lumberjack, and I'm okay
       I sleep all night and I work all day

   [No Values]
   key_without_value
   empty string value here =

   [You can use comments]
   # like this
   ; or this

   # By default only in an empty line.
   # Inline comments can be harmful because they prevent users
   # from using the delimiting characters as parts of values.
   # That being said, this can be customized.

       [Sections Can Be Indented]
           can_values_be_as_well = True
           does_that_mean_anything_special = False
           purpose = formatting for readability
           multiline_values = are
               handled just fine as
               long as they are indented
               deeper than the first line
               of a value
           # Did I mention we can indent comments, too?


Interpolation of values
-----------------------

On top of the core functionality, :class:`ConfigParser` supports
interpolation.  This means values can be preprocessed before returning them
from ``get()`` calls.

.. index:: single: % (percent); interpolation in configuration files

.. class:: BasicInterpolation()

   The default implementation used by :class:`ConfigParser`.  It enables
   values to contain format strings which refer to other values in the same
   section, or values in the special default section [1]_.  Additional default
   values can be provided on initialization.

   For example:

   .. code-block:: ini

      [Paths]
      home_dir: /Users
      my_dir: %(home_dir)s/lumberjack
      my_pictures: %(my_dir)s/Pictures

      [Escape]
      # use a %% to escape the % sign (% is the only character that needs to be escaped):
      gain: 80%%

   In the example above, :class:`ConfigParser` with *interpolation* set to
   ``BasicInterpolation()`` would resolve ``%(home_dir)s`` to the value of
   ``home_dir`` (``/Users`` in this case).  ``%(my_dir)s`` in effect would
   resolve to ``/Users/lumberjack``.  All interpolations are done on demand so
   keys used in the chain of references do not have to be specified in any
   specific order in the configuration file.

   With ``interpolation`` set to ``None``, the parser would simply return
   ``%(my_dir)s/Pictures`` as the value of ``my_pictures`` and
   ``%(home_dir)s/lumberjack`` as the value of ``my_dir``.

.. index:: single: $ (dollar); interpolation in configuration files

.. class:: ExtendedInterpolation()

   An alternative handler for interpolation which implements a more advanced
   syntax, used for instance in ``zc.buildout``.  Extended interpolation is
   using ``${section:option}`` to denote a value from a foreign section.
   Interpolation can span multiple levels.  For convenience, if the
   ``section:`` part is omitted, interpolation defaults to the current section
   (and possibly the default values from the special section).

   For example, the configuration specified above with basic interpolation,
   would look like this with extended interpolation:

   .. code-block:: ini

      [Paths]
      home_dir: /Users
      my_dir: ${home_dir}/lumberjack
      my_pictures: ${my_dir}/Pictures

      [Escape]
      # use a $$ to escape the $ sign ($ is the only character that needs to be escaped):
      cost: $$80

   Values from other sections can be fetched as well:

   .. code-block:: ini

      [Common]
      home_dir: /Users
      library_dir: /Library
      system_dir: /System
      macports_dir: /opt/local

      [Frameworks]
      Python: 3.2
      path: ${Common:system_dir}/Library/Frameworks/

      [Arthur]
      nickname: Two Sheds
      last_name: Jackson
      my_dir: ${Common:home_dir}/twosheds
      my_pictures: ${my_dir}/Pictures
      python_dir: ${Frameworks:path}/Python/Versions/${Frameworks:Python}

Mapping Protocol Access
-----------------------

.. versionadded:: 3.2

Mapping protocol access is a generic name for functionality that enables using
custom objects as if they were dictionaries.  In case of :mod:`configparser`,
the mapping interface implementation is using the
``parser['section']['option']`` notation.

``parser['section']`` in particular returns a proxy for the section's data in
the parser.  This means that the values are not copied but they are taken from
the original parser on demand.  What's even more important is that when values
are changed on a section proxy, they are actually mutated in the original
parser.

:mod:`configparser` objects behave as close to actual dictionaries as possible.
The mapping interface is complete and adheres to the
:class:`~collections.abc.MutableMapping` ABC.
However, there are a few differences that should be taken into account:

* By default, all keys in sections are accessible in a case-insensitive manner
  [1]_.  E.g. ``for option in parser["section"]`` yields only ``optionxform``'ed
  option key names.  This means lowercased keys by default.  At the same time,
  for a section that holds the key ``'a'``, both expressions return ``True``::

     "a" in parser["section"]
     "A" in parser["section"]

* All sections include ``DEFAULTSECT`` values as well which means that
  ``.clear()`` on a section may not leave the section visibly empty.  This is
  because default values cannot be deleted from the section (because technically
  they are not there).  If they are overridden in the section, deleting causes
  the default value to be visible again.  Trying to delete a default value
  causes a :exc:`KeyError`.

* ``DEFAULTSECT`` cannot be removed from the parser:

  * trying to delete it raises :exc:`ValueError`,

  * ``parser.clear()`` leaves it intact,

  * ``parser.popitem()`` never returns it.

* ``parser.get(section, option, **kwargs)`` - the second argument is **not**
  a fallback value.  Note however that the section-level ``get()`` methods are
  compatible both with the mapping protocol and the classic configparser API.

* ``parser.items()`` is compatible with the mapping protocol (returns a list of
  *section_name*, *section_proxy* pairs including the DEFAULTSECT).  However,
  this method can also be invoked with arguments: ``parser.items(section, raw,
  vars)``.  The latter call returns a list of *option*, *value* pairs for
  a specified ``section``, with all interpolations expanded (unless
  ``raw=True`` is provided).

The mapping protocol is implemented on top of the existing legacy API so that
subclasses overriding the original interface still should have mappings working
as expected.


Customizing Parser Behaviour
----------------------------

There are nearly as many INI format variants as there are applications using it.
:mod:`configparser` goes a long way to provide support for the largest sensible
set of INI styles available.  The default functionality is mainly dictated by
historical background and it's very likely that you will want to customize some
of the features.

The most common way to change the way a specific config parser works is to use
the :meth:`!__init__` options:

* *defaults*, default value: ``None``

  This option accepts a dictionary of key-value pairs which will be initially
  put in the ``DEFAULT`` section.  This makes for an elegant way to support
  concise configuration files that don't specify values which are the same as
  the documented default.

  Hint: if you want to specify default values for a specific section, use
  :meth:`~ConfigParser.read_dict` before you read the actual file.

* *dict_type*, default value: :class:`dict`

  This option has a major impact on how the mapping protocol will behave and how
  the written configuration files look.  With the standard dictionary, every
  section is stored in the order they were added to the parser.  Same goes for
  options within sections.

  An alternative dictionary type can be used for example to sort sections and
  options on write-back.

  Please note: there are ways to add a set of key-value pairs in a single
  operation.  When you use a regular dictionary in those operations, the order
  of the keys will be ordered.  For example:

  .. doctest::

     >>> parser = configparser.ConfigParser()
     >>> parser.read_dict({'section1': {'key1': 'value1',
     ...                                'key2': 'value2',
     ...                                'key3': 'value3'},
     ...                   'section2': {'keyA': 'valueA',
     ...                                'keyB': 'valueB',
     ...                                'keyC': 'valueC'},
     ...                   'section3': {'foo': 'x',
     ...                                'bar': 'y',
     ...                                'baz': 'z'}
     ... })
     >>> parser.sections()
     ['section1', 'section2', 'section3']
     >>> [option for option in parser['section3']]
     ['foo', 'bar', 'baz']

* *allow_no_value*, default value: ``False``

  Some configuration files are known to include settings without values, but
  which otherwise conform to the syntax supported by :mod:`configparser`.  The
  *allow_no_value* parameter to the constructor can be used to
  indicate that such values should be accepted:

  .. doctest::

     >>> import configparser

     >>> sample_config = """
     ... [mysqld]
     ...   user = mysql
     ...   pid-file = /var/run/mysqld/mysqld.pid
     ...   skip-external-locking
     ...   old_passwords = 1
     ...   skip-bdb
     ...   # we don't need ACID today
     ...   skip-innodb
     ... """
     >>> config = configparser.ConfigParser(allow_no_value=True)
     >>> config.read_string(sample_config)

     >>> # Settings with values are treated as before:
     >>> config["mysqld"]["user"]
     'mysql'

     >>> # Settings without values provide None:
     >>> config["mysqld"]["skip-bdb"]

     >>> # Settings which aren't specified still raise an error:
     >>> config["mysqld"]["does-not-exist"]
     Traceback (most recent call last):
       ...
     KeyError: 'does-not-exist'

* *delimiters*, default value: ``('=', ':')``

  Delimiters are substrings that delimit keys from values within a section.
  The first occurrence of a delimiting substring on a line is considered
  a delimiter.  This means values (but not keys) can contain the delimiters.

  See also the *space_around_delimiters* argument to
  :meth:`ConfigParser.write`.

* *comment_prefixes*, default value: ``('#', ';')``

* *inline_comment_prefixes*, default value: ``None``

  Comment prefixes are strings that indicate the start of a valid comment within
  a config file. *comment_prefixes* are used only on otherwise empty lines
  (optionally indented) whereas *inline_comment_prefixes* can be used after
  every valid value (e.g. section names, options and empty lines as well).  By
  default inline comments are disabled and ``'#'`` and ``';'`` are used as
  prefixes for whole line comments.

  .. versionchanged:: 3.2
     In previous versions of :mod:`configparser` behaviour matched
     ``comment_prefixes=('#',';')`` and ``inline_comment_prefixes=(';',)``.

  Please note that config parsers don't support escaping of comment prefixes so
  using *inline_comment_prefixes* may prevent users from specifying option
  values with characters used as comment prefixes.  When in doubt, avoid
  setting *inline_comment_prefixes*.  In any circumstances, the only way of
  storing comment prefix characters at the beginning of a line in multiline
  values is to interpolate the prefix, for example::

    >>> from configparser import ConfigParser, ExtendedInterpolation
    >>> parser = ConfigParser(interpolation=ExtendedInterpolation())
    >>> # the default BasicInterpolation could be used as well
    >>> parser.read_string("""
    ... [DEFAULT]
    ... hash = #
    ...
    ... [hashes]
    ... shebang =
    ...   ${hash}!/usr/bin/env python
    ...   ${hash} -*- coding: utf-8 -*-
    ...
    ... extensions =
    ...   enabled_extension
    ...   another_extension
    ...   #disabled_by_comment
    ...   yet_another_extension
    ...
    ... interpolation not necessary = if # is not at line start
    ... even in multiline values = line #1
    ...   line #2
    ...   line #3
    ... """)
    >>> print(parser['hashes']['shebang'])
    <BLANKLINE>
    #!/usr/bin/env python
    # -*- coding: utf-8 -*-
    >>> print(parser['hashes']['extensions'])
    <BLANKLINE>
    enabled_extension
    another_extension
    yet_another_extension
    >>> print(parser['hashes']['interpolation not necessary'])
    if # is not at line start
    >>> print(parser['hashes']['even in multiline values'])
    line #1
    line #2
    line #3

* *strict*, default value: ``True``

  When set to ``True``, the parser will not allow for any section or option
  duplicates while reading from a single source (using :meth:`~ConfigParser.read_file`,
  :meth:`~ConfigParser.read_string` or :meth:`~ConfigParser.read_dict`).  It is recommended to use strict
  parsers in new applications.

  .. versionchanged:: 3.2
     In previous versions of :mod:`configparser` behaviour matched
     ``strict=False``.

* *empty_lines_in_values*, default value: ``True``

  In config parsers, values can span multiple lines as long as they are
  indented more than the key that holds them.  By default parsers also let
  empty lines to be parts of values.  At the same time, keys can be arbitrarily
  indented themselves to improve readability.  In consequence, when
  configuration files get big and complex, it is easy for the user to lose
  track of the file structure.  Take for instance:

  .. code-block:: ini

     [Section]
     key = multiline
       value with a gotcha

      this = is still a part of the multiline value of 'key'

  This can be especially problematic for the user to see if she's using a
  proportional font to edit the file.  That is why when your application does
  not need values with empty lines, you should consider disallowing them.  This
  will make empty lines split keys every time.  In the example above, it would
  produce two keys, ``key`` and ``this``.

* *default_section*, default value: ``configparser.DEFAULTSECT`` (that is:
  ``"DEFAULT"``)

  The convention of allowing a special section of default values for other
  sections or interpolation purposes is a powerful concept of this library,
  letting users create complex declarative configurations.  This section is
  normally called ``"DEFAULT"`` but this can be customized to point to any
  other valid section name.  Some typical values include: ``"general"`` or
  ``"common"``.  The name provided is used for recognizing default sections
  when reading from any source and is used when writing configuration back to
  a file.  Its current value can be retrieved using the
  ``parser_instance.default_section`` attribute and may be modified at runtime
  (i.e. to convert files from one format to another).

* *interpolation*, default value: ``configparser.BasicInterpolation``

  Interpolation behaviour may be customized by providing a custom handler
  through the *interpolation* argument. ``None`` can be used to turn off
  interpolation completely, ``ExtendedInterpolation()`` provides a more
  advanced variant inspired by ``zc.buildout``.  More on the subject in the
  `dedicated documentation section <#interpolation-of-values>`_.
  :class:`RawConfigParser` has a default value of ``None``.

* *converters*, default value: not set

  Config parsers provide option value getters that perform type conversion.  By
  default :meth:`~ConfigParser.getint`, :meth:`~ConfigParser.getfloat`, and
  :meth:`~ConfigParser.getboolean` are implemented.  Should other getters be
  desirable, users may define them in a subclass or pass a dictionary where each
  key is a name of the converter and each value is a callable implementing said
  conversion.  For instance, passing ``{'decimal': decimal.Decimal}`` would add
  :meth:`!getdecimal` on both the parser object and all section proxies.  In
  other words, it will be possible to write both
  ``parser_instance.getdecimal('section', 'key', fallback=0)`` and
  ``parser_instance['section'].getdecimal('key', 0)``.

  If the converter needs to access the state of the parser, it can be
  implemented as a method on a config parser subclass.  If the name of this
  method starts with ``get``, it will be available on all section proxies, in
  the dict-compatible form (see the ``getdecimal()`` example above).

More advanced customization may be achieved by overriding default values of
these parser attributes.  The defaults are defined on the classes, so they may
be overridden by subclasses or by attribute assignment.

.. attribute:: ConfigParser.BOOLEAN_STATES

   By default when using :meth:`~ConfigParser.getboolean`, config parsers
   consider the following values ``True``: ``'1'``, ``'yes'``, ``'true'``,
   ``'on'`` and the following values ``False``: ``'0'``, ``'no'``, ``'false'``,
   ``'off'``.  You can override this by specifying a custom dictionary of strings
   and their Boolean outcomes. For example:

   .. doctest::

      >>> custom = configparser.ConfigParser()
      >>> custom['section1'] = {'funky': 'nope'}
      >>> custom['section1'].getboolean('funky')
      Traceback (most recent call last):
      ...
      ValueError: Not a boolean: nope
      >>> custom.BOOLEAN_STATES = {'sure': True, 'nope': False}
      >>> custom['section1'].getboolean('funky')
      False

   Other typical Boolean pairs include ``accept``/``reject`` or
   ``enabled``/``disabled``.

.. method:: ConfigParser.optionxform(option)
   :noindex:

   This method transforms option names on every read, get, or set
   operation.  The default converts the name to lowercase.  This also
   means that when a configuration file gets written, all keys will be
   lowercase.  Override this method if that's unsuitable.
   For example:

   .. doctest::

      >>> config = """
      ... [Section1]
      ... Key = Value
      ...
      ... [Section2]
      ... AnotherKey = Value
      ... """
      >>> typical = configparser.ConfigParser()
      >>> typical.read_string(config)
      >>> list(typical['Section1'].keys())
      ['key']
      >>> list(typical['Section2'].keys())
      ['anotherkey']
      >>> custom = configparser.RawConfigParser()
      >>> custom.optionxform = lambda option: option
      >>> custom.read_string(config)
      >>> list(custom['Section1'].keys())
      ['Key']
      >>> list(custom['Section2'].keys())
      ['AnotherKey']

   .. note::
      The optionxform function transforms option names to a canonical form.
      This should be an idempotent function: if the name is already in
      canonical form, it should be returned unchanged.


.. attribute:: ConfigParser.SECTCRE

   A compiled regular expression used to parse section headers.  The default
   matches ``[section]`` to the name ``"section"``.  Whitespace is considered
   part of the section name, thus ``[  larch  ]`` will be read as a section of
   name ``"  larch  "``.  Override this attribute if that's unsuitable.  For
   example:

   .. doctest::

      >>> import re
      >>> config = """
      ... [Section 1]
      ... option = value
      ...
      ... [  Section 2  ]
      ... another = val
      ... """
      >>> typical = configparser.ConfigParser()
      >>> typical.read_string(config)
      >>> typical.sections()
      ['Section 1', '  Section 2  ']
      >>> custom = configparser.ConfigParser()
      >>> custom.SECTCRE = re.compile(r"\[ *(?P<header>[^]]+?) *\]")
      >>> custom.read_string(config)
      >>> custom.sections()
      ['Section 1', 'Section 2']

   .. note::

      While ConfigParser objects also use an ``OPTCRE`` attribute for recognizing
      option lines, it's not recommended to override it because that would
      interfere with constructor options *allow_no_value* and *delimiters*.


Legacy API Examples
-------------------

Mainly because of backwards compatibility concerns, :mod:`configparser`
provides also a legacy API with explicit ``get``/``set`` methods.  While there
are valid use cases for the methods outlined below, mapping protocol access is
preferred for new projects.  The legacy API is at times more advanced,
low-level and downright counterintuitive.

An example of writing to a configuration file::

   import configparser

   config = configparser.RawConfigParser()

   # Please note that using RawConfigParser's set functions, you can assign
   # non-string values to keys internally, but will receive an error when
   # attempting to write to a file or when you get it in non-raw mode. Setting
   # values using the mapping protocol or ConfigParser's set() does not allow
   # such assignments to take place.
   config.add_section('Section1')
   config.set('Section1', 'an_int', '15')
   config.set('Section1', 'a_bool', 'true')
   config.set('Section1', 'a_float', '3.1415')
   config.set('Section1', 'baz', 'fun')
   config.set('Section1', 'bar', 'Python')
   config.set('Section1', 'foo', '%(bar)s is %(baz)s!')

   # Writing our configuration file to 'example.cfg'
   with open('example.cfg', 'w') as configfile:
       config.write(configfile)

An example of reading the configuration file again::

   import configparser

   config = configparser.RawConfigParser()
   config.read('example.cfg')

   # getfloat() raises an exception if the value is not a float
   # getint() and getboolean() also do this for their respective types
   a_float = config.getfloat('Section1', 'a_float')
   an_int = config.getint('Section1', 'an_int')
   print(a_float + an_int)

   # Notice that the next output does not interpolate '%(bar)s' or '%(baz)s'.
   # This is because we are using a RawConfigParser().
   if config.getboolean('Section1', 'a_bool'):
       print(config.get('Section1', 'foo'))

To get interpolation, use :class:`ConfigParser`::

   import configparser

   cfg = configparser.ConfigParser()
   cfg.read('example.cfg')

   # Set the optional *raw* argument of get() to True if you wish to disable
   # interpolation in a single get operation.
   print(cfg.get('Section1', 'foo', raw=False))  # -> "Python is fun!"
   print(cfg.get('Section1', 'foo', raw=True))   # -> "%(bar)s is %(baz)s!"

   # The optional *vars* argument is a dict with members that will take
   # precedence in interpolation.
   print(cfg.get('Section1', 'foo', vars={'bar': 'Documentation',
                                          'baz': 'evil'}))

   # The optional *fallback* argument can be used to provide a fallback value
   print(cfg.get('Section1', 'foo'))
         # -> "Python is fun!"

   print(cfg.get('Section1', 'foo', fallback='Monty is not.'))
         # -> "Python is fun!"

   print(cfg.get('Section1', 'monster', fallback='No such things as monsters.'))
         # -> "No such things as monsters."

   # A bare print(cfg.get('Section1', 'monster')) would raise NoOptionError
   # but we can also use:

   print(cfg.get('Section1', 'monster', fallback=None))
         # -> None

Default values are available in both types of ConfigParsers.  They are used in
interpolation if an option used is not defined elsewhere. ::

   import configparser

   # New instance with 'bar' and 'baz' defaulting to 'Life' and 'hard' each
   config = configparser.ConfigParser({'bar': 'Life', 'baz': 'hard'})
   config.read('example.cfg')

   print(config.get('Section1', 'foo'))     # -> "Python is fun!"
   config.remove_option('Section1', 'bar')
   config.remove_option('Section1', 'baz')
   print(config.get('Section1', 'foo'))     # -> "Life is hard!"


.. _configparser-objects:

ConfigParser Objects
--------------------

.. class:: ConfigParser(defaults=None, dict_type=dict, allow_no_value=False, delimiters=('=', ':'), comment_prefixes=('#', ';'), inline_comment_prefixes=None, strict=True, empty_lines_in_values=True, default_section=configparser.DEFAULTSECT, interpolation=BasicInterpolation(), converters={})

   The main configuration parser.  When *defaults* is given, it is initialized
   into the dictionary of intrinsic defaults.  When *dict_type* is given, it
   will be used to create the dictionary objects for the list of sections, for
   the options within a section, and for the default values.

   When *delimiters* is given, it is used as the set of substrings that
   divide keys from values.  When *comment_prefixes* is given, it will be used
   as the set of substrings that prefix comments in otherwise empty lines.
   Comments can be indented.  When *inline_comment_prefixes* is given, it will
   be used as the set of substrings that prefix comments in non-empty lines.

   When *strict* is ``True`` (the default), the parser won't allow for
   any section or option duplicates while reading from a single source (file,
   string or dictionary), raising :exc:`DuplicateSectionError` or
   :exc:`DuplicateOptionError`.  When *empty_lines_in_values* is ``False``
   (default: ``True``), each empty line marks the end of an option.  Otherwise,
   internal empty lines of a multiline option are kept as part of the value.
   When *allow_no_value* is ``True`` (default: ``False``), options without
   values are accepted; the value held for these is ``None`` and they are
   serialized without the trailing delimiter.

   When *default_section* is given, it specifies the name for the special
   section holding default values for other sections and interpolation purposes
   (normally named ``"DEFAULT"``).  This value can be retrieved and changed at
   runtime using the ``default_section`` instance attribute. This won't
   re-evaluate an already parsed config file, but will be used when writing
   parsed settings to a new config file.

   Interpolation behaviour may be customized by providing a custom handler
   through the *interpolation* argument. ``None`` can be used to turn off
   interpolation completely, ``ExtendedInterpolation()`` provides a more
   advanced variant inspired by ``zc.buildout``.  More on the subject in the
   `dedicated documentation section <#interpolation-of-values>`_.

   All option names used in interpolation will be passed through the
   :meth:`optionxform` method just like any other option name reference.  For
   example, using the default implementation of :meth:`optionxform` (which
   converts option names to lower case), the values ``foo %(bar)s`` and ``foo
   %(BAR)s`` are equivalent.

   When *converters* is given, it should be a dictionary where each key
   represents the name of a type converter and each value is a callable
   implementing the conversion from string to the desired datatype.  Every
   converter gets its own corresponding :meth:`!get*()` method on the parser
   object and section proxies.

   .. versionchanged:: 3.1
      The default *dict_type* is :class:`collections.OrderedDict`.

   .. versionchanged:: 3.2
      *allow_no_value*, *delimiters*, *comment_prefixes*, *strict*,
      *empty_lines_in_values*, *default_section* and *interpolation* were
      added.

   .. versionchanged:: 3.5
      The *converters* argument was added.

   .. versionchanged:: 3.7
      The *defaults* argument is read with :meth:`read_dict()`,
      providing consistent behavior across the parser: non-string
      keys and values are implicitly converted to strings.

   .. versionchanged:: 3.8
      The default *dict_type* is :class:`dict`, since it now preserves
      insertion order.

   .. method:: defaults()

      Return a dictionary containing the instance-wide defaults.


   .. method:: sections()

      Return a list of the sections available; the *default section* is not
      included in the list.


   .. method:: add_section(section)

      Add a section named *section* to the instance.  If a section by the given
      name already exists, :exc:`DuplicateSectionError` is raised.  If the
      *default section* name is passed, :exc:`ValueError` is raised.  The name
      of the section must be a string; if not, :exc:`TypeError` is raised.

      .. versionchanged:: 3.2
         Non-string section names raise :exc:`TypeError`.


   .. method:: has_section(section)

      Indicates whether the named *section* is present in the configuration.
      The *default section* is not acknowledged.


   .. method:: options(section)

      Return a list of options available in the specified *section*.


   .. method:: has_option(section, option)

      If the given *section* exists, and contains the given *option*, return
      :const:`True`; otherwise return :const:`False`.  If the specified
      *section* is :const:`None` or an empty string, DEFAULT is assumed.


   .. method:: read(filenames, encoding=None)

      Attempt to read and parse an iterable of filenames, returning a list of
      filenames which were successfully parsed.

      If *filenames* is a string, a :class:`bytes` object or a
      :term:`path-like object`, it is treated as
      a single filename.  If a file named in *filenames* cannot be opened, that
      file will be ignored.  This is designed so that you can specify an
      iterable of potential configuration file locations (for example, the
      current directory, the user's home directory, and some system-wide
      directory), and all existing configuration files in the iterable will be
      read.

      If none of the named files exist, the :class:`ConfigParser`
      instance will contain an empty dataset.  An application which requires
      initial values to be loaded from a file should load the required file or
      files using :meth:`read_file` before calling :meth:`read` for any
      optional files::

         import configparser, os

         config = configparser.ConfigParser()
         config.read_file(open('defaults.cfg'))
         config.read(['site.cfg', os.path.expanduser('~/.myapp.cfg')],
                     encoding='cp1250')

      .. versionchanged:: 3.2
         Added the *encoding* parameter.
         Previously, all files were read using the default encoding for :func:`open`.

      .. versionchanged:: 3.6.1
         The *filenames* parameter accepts a :term:`path-like object`.

      .. versionchanged:: 3.7
         The *filenames* parameter accepts a :class:`bytes` object.


   .. method:: read_file(f, source=None)

      Read and parse configuration data from *f* which must be an iterable
      yielding Unicode strings (for example files opened in text mode).

      Optional argument *source* specifies the name of the file being read.  If
      not given and *f* has a :attr:`!name` attribute, that is used for
      *source*; the default is ``'<???>'``.

      .. versionadded:: 3.2
         Replaces :meth:`!readfp`.

   .. method:: read_string(string, source='<string>')

      Parse configuration data from a string.

      Optional argument *source* specifies a context-specific name of the
      string passed.  If not given, ``'<string>'`` is used.  This should
      commonly be a filesystem path or a URL.

      .. versionadded:: 3.2


   .. method:: read_dict(dictionary, source='<dict>')

      Load configuration from any object that provides a dict-like ``items()``
      method.  Keys are section names, values are dictionaries with keys and
      values that should be present in the section.  If the used dictionary
      type preserves order, sections and their keys will be added in order.
      Values are automatically converted to strings.

      Optional argument *source* specifies a context-specific name of the
      dictionary passed.  If not given, ``<dict>`` is used.

      This method can be used to copy state between parsers.

      .. versionadded:: 3.2


   .. method:: get(section, option, *, raw=False, vars=None[, fallback])

      Get an *option* value for the named *section*.  If *vars* is provided, it
      must be a dictionary.  The *option* is looked up in *vars* (if provided),
      *section*, and in *DEFAULTSECT* in that order.  If the key is not found
      and *fallback* is provided, it is used as a fallback value.  ``None`` can
      be provided as a *fallback* value.

      All the ``'%'`` interpolations are expanded in the return values, unless
      the *raw* argument is true.  Values for interpolation keys are looked up
      in the same manner as the option.

      .. versionchanged:: 3.2
         Arguments *raw*, *vars* and *fallback* are keyword only to protect
         users from trying to use the third argument as the *fallback* fallback
         (especially when using the mapping protocol).


   .. method:: getint(section, option, *, raw=False, vars=None[, fallback])

      A convenience method which coerces the *option* in the specified *section*
      to an integer.  See :meth:`get` for explanation of *raw*, *vars* and
      *fallback*.


   .. method:: getfloat(section, option, *, raw=False, vars=None[, fallback])

      A convenience method which coerces the *option* in the specified *section*
      to a floating point number.  See :meth:`get` for explanation of *raw*,
      *vars* and *fallback*.


   .. method:: getboolean(section, option, *, raw=False, vars=None[, fallback])

      A convenience method which coerces the *option* in the specified *section*
      to a Boolean value.  Note that the accepted values for the option are
      ``'1'``, ``'yes'``, ``'true'``, and ``'on'``, which cause this method to
      return ``True``, and ``'0'``, ``'no'``, ``'false'``, and ``'off'``, which
      cause it to return ``False``.  These string values are checked in a
      case-insensitive manner.  Any other value will cause it to raise
      :exc:`ValueError`.  See :meth:`get` for explanation of *raw*, *vars* and
      *fallback*.


   .. method:: items(raw=False, vars=None)
               items(section, raw=False, vars=None)

      When *section* is not given, return a list of *section_name*,
      *section_proxy* pairs, including DEFAULTSECT.

      Otherwise, return a list of *name*, *value* pairs for the options in the
      given *section*.  Optional arguments have the same meaning as for the
      :meth:`get` method.

      .. versionchanged:: 3.8
         Items present in *vars* no longer appear in the result.  The previous
         behaviour mixed actual parser options with variables provided for
         interpolation.


   .. method:: set(section, option, value)

      If the given section exists, set the given option to the specified value;
      otherwise raise :exc:`NoSectionError`.  *option* and *value* must be
      strings; if not, :exc:`TypeError` is raised.


   .. method:: write(fileobject, space_around_delimiters=True)

      Write a representation of the configuration to the specified :term:`file
      object`, which must be opened in text mode (accepting strings).  This
      representation can be parsed by a future :meth:`read` call.  If
      *space_around_delimiters* is true, delimiters between
      keys and values are surrounded by spaces.

   .. note::

      Comments in the original configuration file are not preserved when
      writing the configuration back.
      What is considered a comment, depends on the given values for
      *comment_prefix* and *inline_comment_prefix*.


   .. method:: remove_option(section, option)

      Remove the specified *option* from the specified *section*.  If the
      section does not exist, raise :exc:`NoSectionError`.  If the option
      existed to be removed, return :const:`True`; otherwise return
      :const:`False`.


   .. method:: remove_section(section)

      Remove the specified *section* from the configuration.  If the section in
      fact existed, return ``True``.  Otherwise return ``False``.


   .. method:: optionxform(option)

      Transforms the option name *option* as found in an input file or as passed
      in by client code to the form that should be used in the internal
      structures.  The default implementation returns a lower-case version of
      *option*; subclasses may override this or client code can set an attribute
      of this name on instances to affect this behavior.

      You don't need to subclass the parser to use this method, you can also
      set it on an instance, to a function that takes a string argument and
      returns a string.  Setting it to ``str``, for example, would make option
      names case sensitive::

         cfgparser = ConfigParser()
         cfgparser.optionxform = str

      Note that when reading configuration files, whitespace around the option
      names is stripped before :meth:`optionxform` is called.


   .. method:: readfp(fp, filename=None)

      .. deprecated:: 3.2
         Use :meth:`read_file` instead.

      .. versionchanged:: 3.2
         :meth:`readfp` now iterates on *fp* instead of calling ``fp.readline()``.

      For existing code calling :meth:`readfp` with arguments which don't
      support iteration, the following generator may be used as a wrapper
      around the file-like object::

         def readline_generator(fp):
             line = fp.readline()
             while line:
                 yield line
                 line = fp.readline()

      Instead of ``parser.readfp(fp)`` use
      ``parser.read_file(readline_generator(fp))``.


.. data:: MAX_INTERPOLATION_DEPTH

   The maximum depth for recursive interpolation for :meth:`~configparser.ConfigParser.get` when the *raw*
   parameter is false.  This is relevant only when the default *interpolation*
   is used.


.. _rawconfigparser-objects:

RawConfigParser Objects
-----------------------

.. class:: RawConfigParser(defaults=None, dict_type=dict, \
                           allow_no_value=False, *, delimiters=('=', ':'), \
                           comment_prefixes=('#', ';'), \
                           inline_comment_prefixes=None, strict=True, \
                           empty_lines_in_values=True, \
                           default_section=configparser.DEFAULTSECT[, \
                           interpolation])

   Legacy variant of the :class:`ConfigParser`.  It has interpolation
   disabled by default and allows for non-string section names, option
   names, and values via its unsafe ``add_section`` and ``set`` methods,
   as well as the legacy ``defaults=`` keyword argument handling.

   .. versionchanged:: 3.8
      The default *dict_type* is :class:`dict`, since it now preserves
      insertion order.

   .. note::
      Consider using :class:`ConfigParser` instead which checks types of
      the values to be stored internally.  If you don't want interpolation, you
      can use ``ConfigParser(interpolation=None)``.


   .. method:: add_section(section)

      Add a section named *section* to the instance.  If a section by the given
      name already exists, :exc:`DuplicateSectionError` is raised.  If the
      *default section* name is passed, :exc:`ValueError` is raised.

      Type of *section* is not checked which lets users create non-string named
      sections.  This behaviour is unsupported and may cause internal errors.


   .. method:: set(section, option, value)

      If the given section exists, set the given option to the specified value;
      otherwise raise :exc:`NoSectionError`.  While it is possible to use
      :class:`RawConfigParser` (or :class:`ConfigParser` with *raw* parameters
      set to true) for *internal* storage of non-string values, full
      functionality (including interpolation and output to files) can only be
      achieved using string values.

      This method lets users assign non-string values to keys internally.  This
      behaviour is unsupported and will cause errors when attempting to write
      to a file or get it in non-raw mode.  **Use the mapping protocol API**
      which does not allow such assignments to take place.


Exceptions
----------

.. exception:: Error

   Base class for all other :mod:`configparser` exceptions.


.. exception:: NoSectionError

   Exception raised when a specified section is not found.


.. exception:: DuplicateSectionError

   Exception raised if :meth:`~ConfigParser.add_section` is called with the name of a section
   that is already present or in strict parsers when a section if found more
   than once in a single input file, string or dictionary.

   .. versionchanged:: 3.2
      Added the optional *source* and *lineno* attributes and parameters to
      :meth:`!__init__`.


.. exception:: DuplicateOptionError

   Exception raised by strict parsers if a single option appears twice during
   reading from a single file, string or dictionary. This catches misspellings
   and case sensitivity-related errors, e.g. a dictionary may have two keys
   representing the same case-insensitive configuration key.


.. exception:: NoOptionError

   Exception raised when a specified option is not found in the specified
   section.


.. exception:: InterpolationError

   Base class for exceptions raised when problems occur performing string
   interpolation.


.. exception:: InterpolationDepthError

   Exception raised when string interpolation cannot be completed because the
   number of iterations exceeds :const:`MAX_INTERPOLATION_DEPTH`.  Subclass of
   :exc:`InterpolationError`.


.. exception:: InterpolationMissingOptionError

   Exception raised when an option referenced from a value does not exist.
   Subclass of :exc:`InterpolationError`.


.. exception:: InterpolationSyntaxError

   Exception raised when the source text into which substitutions are made does
   not conform to the required syntax.  Subclass of :exc:`InterpolationError`.


.. exception:: MissingSectionHeaderError

   Exception raised when attempting to parse a file which has no section
   headers.


.. exception:: ParsingError

   Exception raised when errors occur attempting to parse a file.

   .. versionchanged:: 3.2
      The ``filename`` attribute and :meth:`!__init__` argument were renamed to
      ``source`` for consistency.


.. rubric:: Footnotes

.. [1] Config parsers allow for heavy customization.  If you are interested in
       changing the behaviour outlined by the footnote reference, consult the
       `Customizing Parser Behaviour`_ section.