githubmirror/cpython

Doc/library/pprint.rst
434 строки16 KB
Hugo van Kemenade
Python 3.15.0b1
07 май 2026, 16:26
07 май 2026, 16:26f31a89b
:mod:`!pprint` --- Data pretty printer
======================================

.. module:: pprint
   :synopsis: Data pretty printer.

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

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

The :mod:`!pprint` module provides a capability to "pretty-print" arbitrary
Python data structures in a form which can be used as input to the interpreter.
If the formatted structures include objects which are not fundamental Python
types, the representation may not be loadable.  This may be the case if objects
such as files, sockets or classes are included, as well as many other
objects which are not representable as Python literals.

The formatted representation keeps objects on a single line if it can, and
breaks them onto multiple lines if they don't fit within the allowed width,
adjustable by the *width* parameter defaulting to 88 characters.

.. versionchanged:: 3.9
   Added support for pretty-printing :class:`types.SimpleNamespace`.

.. versionchanged:: 3.10
   Added support for pretty-printing :class:`dataclasses.dataclass`.

.. _pprint-functions:

Functions
---------

.. function:: pp(object, stream=None, indent=4, width=88, depth=None, *, \
                 compact=False, sort_dicts=False, underscore_numbers=False)

   Prints the formatted representation of *object*, followed by a newline.
   This function may be used in the interactive interpreter
   instead of the :func:`print` function for inspecting values.
   Tip: you can reassign ``print = pprint.pp`` for use within a scope.

   :param object:
      The object to be printed.

   :param stream:
      A file-like object to which the output will be written
      by calling its :meth:`!write` method.
      If ``None`` (the default), :data:`sys.stdout` is used.
   :type stream: :term:`file-like object` | None

   :param int indent:
      The amount of indentation added for each nesting level.

   :param int width:
      The desired maximum number of characters per line in the output.
      If a structure cannot be formatted within the width constraint,
      a best effort will be made.

   :param depth:
      The number of nesting levels which may be printed.
      If the data structure being printed is too deep,
      the next contained level is replaced by ``...``.
      If ``None`` (the default), there is no constraint
      on the depth of the objects being formatted.
   :type depth: int | None

   :param bool compact:
      Control the way long :term:`sequences <sequence>` are formatted.
      If ``False`` (the default),
      opening parentheses and brackets will be followed by a newline and the
      following content will be indented by one level, similar to
      pretty-printed JSON.
      If ``True``, as many items as will fit within the *width*
      will be formatted on each output line.

   :param bool sort_dicts:
      If ``True``, dictionaries will be formatted with
      their keys sorted, otherwise
      they will be displayed in insertion order (the default).

   :param bool underscore_numbers:
      If ``True``,
      integers will be formatted with the ``_`` character for a thousands separator,
      otherwise underscores are not displayed (the default).

   >>> import pprint
   >>> stuff = ['spam', 'eggs', 'lumberjack', 'knights', 'ni']
   >>> stuff.insert(0, stuff)
   >>> pprint.pp(stuff, width=100)
   [<Recursion on list with id=...>, 'spam', 'eggs', 'lumberjack', 'knights', 'ni']

   .. versionadded:: 3.8


.. function:: pprint(object, stream=None, indent=4, width=88, depth=None, *, \
                     compact=False, sort_dicts=True, underscore_numbers=False)

   Alias for :func:`~pprint.pp` with *sort_dicts* set to ``True`` by default,
   which would automatically sort the dictionaries' keys,
   you might want to use :func:`~pprint.pp` instead where it is ``False`` by default.


.. function:: pformat(object, indent=4, width=88, depth=None, *, \
                      compact=False, sort_dicts=True, underscore_numbers=False)

   Return the formatted representation of *object* as a string.  *indent*,
   *width*, *depth*, *compact*, *sort_dicts* and *underscore_numbers* are
   passed to the :class:`PrettyPrinter` constructor as formatting parameters
   and their meanings are as described in the documentation above.


.. function:: isreadable(object)

   .. index:: pair: built-in function; eval

   Determine if the formatted representation of *object* is "readable", or can be
   used to reconstruct the value using :func:`eval`.  This always returns ``False``
   for recursive objects.

      >>> pprint.isreadable(stuff)
      False


.. function:: isrecursive(object)

   Determine if *object* requires a recursive representation.  This function is
   subject to the same limitations as noted in :func:`saferepr` below and may raise an
   :exc:`RecursionError` if it fails to detect a recursive object.


.. function:: saferepr(object)

   Return a string representation of *object*, protected against recursion in
   some common data structures, namely instances of :class:`dict`, :class:`list`
   and :class:`tuple` or subclasses whose ``__repr__`` has not been overridden.  If the
   representation of object exposes a recursive entry, the recursive reference
   will be represented as ``<Recursion on typename with id=number>``.  The
   representation is not otherwise formatted.

   >>> pprint.saferepr(stuff)
   "[<Recursion on list with id=...>, 'spam', 'eggs', 'lumberjack', 'knights', 'ni']"

.. _prettyprinter-objects:

PrettyPrinter objects
---------------------

.. index:: single: ...; placeholder

.. class:: PrettyPrinter(indent=4, width=88, depth=None, stream=None, *, \
                         compact=False, sort_dicts=True, \
                         underscore_numbers=False)

   Construct a :class:`PrettyPrinter` instance.

   Arguments have the same meaning as for :func:`~pprint.pp`.
   Note that they are in a different order, and that *sort_dicts* defaults to ``True``.

   >>> import pprint
   >>> stuff = ['spam', 'eggs', 'lumberjack', 'knights', 'ni']
   >>> stuff.insert(0, stuff[:])
   >>> pp = pprint.PrettyPrinter()
   >>> pp.pprint(stuff)
   [
       ['spam', 'eggs', 'lumberjack', 'knights', 'ni'],
       'spam',
       'eggs',
       'lumberjack',
       'knights',
       'ni',
   ]
   >>> pp = pprint.PrettyPrinter(indent=1, width=41, compact=True)
   >>> pp.pprint(stuff)
   [['spam', 'eggs', 'lumberjack',
     'knights', 'ni'],
    'spam', 'eggs', 'lumberjack', 'knights',
    'ni']
   >>> pp = pprint.PrettyPrinter(width=41, indent=3)
   >>> pp.pprint(stuff)
   [
      [
         'spam',
         'eggs',
         'lumberjack',
         'knights',
         'ni',
      ],
      'spam',
      'eggs',
      'lumberjack',
      'knights',
      'ni',
   ]
   >>> tup = ('spam', ('eggs', ('lumberjack', ('knights', ('ni', ('dead',
   ... ('parrot', ('fresh fruit',))))))))
   >>> pp = pprint.PrettyPrinter(depth=6)
   >>> pp.pprint(tup)
   ('spam', ('eggs', ('lumberjack', ('knights', ('ni', ('dead', (...)))))))


   .. versionchanged:: 3.4
      Added the *compact* parameter.

   .. versionchanged:: 3.8
      Added the *sort_dicts* parameter.

   .. versionchanged:: 3.10
      Added the *underscore_numbers* parameter.

   .. versionchanged:: 3.11
      No longer attempts to write to :data:`!sys.stdout` if it is ``None``.

   .. versionchanged:: 3.15
      Changed default *indent* from 1 to 4
      and default *width* from 80 to 88.
      The default ``compact=False`` layout is now similar to
      pretty-printed JSON, with opening parentheses and brackets
      followed by a newline and the contents indented by one level.


:class:`PrettyPrinter` instances have the following methods:


.. method:: PrettyPrinter.pformat(object)

   Return the formatted representation of *object*.  This takes into account the
   options passed to the :class:`PrettyPrinter` constructor.


.. method:: PrettyPrinter.pprint(object)

   Print the formatted representation of *object* on the configured stream,
   followed by a newline.

The following methods provide the implementations for the corresponding
functions of the same names.  Using these methods on an instance is slightly
more efficient since new :class:`PrettyPrinter` objects don't need to be
created.


.. method:: PrettyPrinter.isreadable(object)

   .. index:: pair: built-in function; eval

   Determine if the formatted representation of the object is "readable," or can be
   used to reconstruct the value using :func:`eval`.  Note that this returns
   ``False`` for recursive objects.  If the *depth* parameter of the
   :class:`PrettyPrinter` is set and the object is deeper than allowed, this
   returns ``False``.


.. method:: PrettyPrinter.isrecursive(object)

   Determine if the object requires a recursive representation.

This method is provided as a hook to allow subclasses to modify the way objects
are converted to strings.  The default implementation uses the internals of the
:func:`saferepr` implementation.


.. method:: PrettyPrinter.format(object, context, maxlevels, level)

   Returns three values: the formatted version of *object* as a string, a flag
   indicating whether the result is readable, and a flag indicating whether
   recursion was detected.  The first argument is the object to be presented.  The
   second is a dictionary which contains the :func:`id` of objects that are part of
   the current presentation context (direct and indirect containers for *object*
   that are affecting the presentation) as the keys; if an object needs to be
   presented which is already represented in *context*, the third return value
   should be ``True``.  Recursive calls to the :meth:`.format` method should add
   additional entries for containers to this dictionary.  The third argument,
   *maxlevels*, gives the requested limit to recursion; this will be ``0`` if there
   is no requested limit.  This argument should be passed unmodified to recursive
   calls. The fourth argument, *level*, gives the current level; recursive calls
   should be passed a value less than that of the current call.


.. _pprint-example:

Example
-------

To demonstrate several uses of the :func:`~pprint.pp` function and its parameters,
let's fetch information about a project from `PyPI <https://pypi.org>`_::

   >>> import json
   >>> import pprint
   >>> from urllib.request import urlopen
   >>> with urlopen('https://pypi.org/pypi/sampleproject/1.2.0/json') as resp:
   ...     project_info = json.load(resp)['info']

In its basic form, :func:`~pprint.pp` shows the whole object::

   >>> pprint.pp(project_info)
   {
       'author': 'The Python Packaging Authority',
       'author_email': 'pypa-dev@googlegroups.com',
       'bugtrack_url': None,
       'classifiers': [
           'Development Status :: 3 - Alpha',
           'Intended Audience :: Developers',
           'License :: OSI Approved :: MIT License',
           'Programming Language :: Python :: 2',
           'Programming Language :: Python :: 2.6',
           'Programming Language :: Python :: 2.7',
           'Programming Language :: Python :: 3',
           'Programming Language :: Python :: 3.2',
           'Programming Language :: Python :: 3.3',
           'Programming Language :: Python :: 3.4',
           'Topic :: Software Development :: Build Tools',
       ],
       'description': 'A sample Python project\n'
       '=======================\n'
       '\n'
       'This is the description file for the project.\n'
       '\n'
       'The file should use UTF-8 encoding and be written using ReStructured Text. It\n'
       'will be used to generate the project webpage on PyPI, and should be written for\n'
       'that purpose.\n'
       '\n'
       'Typical contents for this file would include an overview of the project, basic\n'
       'usage examples, etc. Generally, including the project changelog in here is not\n'
       'a good idea, although a simple "What\'s New" section for the most recent version\n'
       'may be appropriate.',
       'description_content_type': None,
       'docs_url': None,
       'download_url': 'UNKNOWN',
       'downloads': {'last_day': -1, 'last_month': -1, 'last_week': -1},
       'home_page': 'https://github.com/pypa/sampleproject',
       'keywords': 'sample setuptools development',
       'license': 'MIT',
       'maintainer': None,
       'maintainer_email': None,
       'name': 'sampleproject',
       'package_url': 'https://pypi.org/project/sampleproject/',
       'platform': 'UNKNOWN',
       'project_url': 'https://pypi.org/project/sampleproject/',
       'project_urls': {'Download': 'UNKNOWN', 'Homepage': 'https://github.com/pypa/sampleproject'},
       'release_url': 'https://pypi.org/project/sampleproject/1.2.0/',
       'requires_dist': None,
       'requires_python': None,
       'summary': 'A sample Python project',
       'version': '1.2.0',
   }

The result can be limited to a certain *depth* (ellipsis is used for deeper
contents)::

   >>> pprint.pp(project_info, depth=1)
   {
       'author': 'The Python Packaging Authority',
       'author_email': 'pypa-dev@googlegroups.com',
       'bugtrack_url': None,
       'classifiers': [...],
       'description': 'A sample Python project\n'
       '=======================\n'
       '\n'
       'This is the description file for the project.\n'
       '\n'
       'The file should use UTF-8 encoding and be written using ReStructured Text. It\n'
       'will be used to generate the project webpage on PyPI, and should be written for\n'
       'that purpose.\n'
       '\n'
       'Typical contents for this file would include an overview of the project, basic\n'
       'usage examples, etc. Generally, including the project changelog in here is not\n'
       'a good idea, although a simple "What\'s New" section for the most recent version\n'
       'may be appropriate.',
       'description_content_type': None,
       'docs_url': None,
       'download_url': 'UNKNOWN',
       'downloads': {...},
       'home_page': 'https://github.com/pypa/sampleproject',
       'keywords': 'sample setuptools development',
       'license': 'MIT',
       'maintainer': None,
       'maintainer_email': None,
       'name': 'sampleproject',
       'package_url': 'https://pypi.org/project/sampleproject/',
       'platform': 'UNKNOWN',
       'project_url': 'https://pypi.org/project/sampleproject/',
       'project_urls': {...},
       'release_url': 'https://pypi.org/project/sampleproject/1.2.0/',
       'requires_dist': None,
       'requires_python': None,
       'summary': 'A sample Python project',
       'version': '1.2.0',
   }

Additionally, maximum character *width* can be suggested. If a long object
cannot be split, the specified width will be exceeded::

   >>> pprint.pp(project_info, depth=1, width=60)
   {
       'author': 'The Python Packaging Authority',
       'author_email': 'pypa-dev@googlegroups.com',
       'bugtrack_url': None,
       'classifiers': [...],
       'description': 'A sample Python project\n'
       '=======================\n'
       '\n'
       'This is the description file for the project.\n'
       '\n'
       'The file should use UTF-8 encoding and be written '
       'using ReStructured Text. It\n'
       'will be used to generate the project webpage on PyPI, '
       'and should be written for\n'
       'that purpose.\n'
       '\n'
       'Typical contents for this file would include an '
       'overview of the project, basic\n'
       'usage examples, etc. Generally, including the project '
       'changelog in here is not\n'
       'a good idea, although a simple "What\'s New" section '
       'for the most recent version\n'
       'may be appropriate.',
       'description_content_type': None,
       'docs_url': None,
       'download_url': 'UNKNOWN',
       'downloads': {...},
       'home_page': 'https://github.com/pypa/sampleproject',
       'keywords': 'sample setuptools development',
       'license': 'MIT',
       'maintainer': None,
       'maintainer_email': None,
       'name': 'sampleproject',
       'package_url': 'https://pypi.org/project/sampleproject/',
       'platform': 'UNKNOWN',
       'project_url': 'https://pypi.org/project/sampleproject/',
       'project_urls': {...},
       'release_url': 'https://pypi.org/project/sampleproject/1.2.0/',
       'requires_dist': None,
       'requires_python': None,
       'summary': 'A sample Python project',
       'version': '1.2.0',
   }