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: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 80 characters.

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


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


.. versionchanged:: 3.15
   Added support for the :ref:`__pprint__ <dunder-pprint>` protocol.

Functions

.. function:: pp(object, stream=None, indent=1, width=80, 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),
      each item of a sequence will be formatted on a separate line,
      otherwise 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)
   [<Recursion on list with id=...>,
    'spam',
    'eggs',
    'lumberjack',
    'knights',
    'ni']

   .. versionadded:: 3.8



.. function:: pprint(object, stream=None, indent=1, width=80, 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=1, width=80, 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

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

: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.

The "__pprint__" protocol

Pretty printing uses an object's __repr__ by default. For custom pretty printing, objects can implement a __pprint__() function to customize how their representations will be printed. If this method exists, it is called instead of __repr__. The method is called with a single argument, the object to be pretty printed.

The method is expected to return or yield a sequence of values, which are used to construct a pretty representation of the object. These values are wrapped in standard class "chrome", such as the class name. The printed representation will usually look like a class constructor, with positional, keyword, and default arguments. The values can be any of the following formats:

  • A single value, representing a positional argument. The value itself is used.
  • A 2-tuple of (name, value) representing a keyword argument. A representation of name=value is used.
  • A 3-tuple of (name, value, default_value) representing a keyword argument with a default value. If value equals default_value, then this tuple is skipped, otherwise name=value is used.

Note

This protocol is compatible with the Rich library's pretty printing protocol.

See the :ref:`pprint-protocol-example` for how this can be used in practice.

Example

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

>>> 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'}

Pretty Print Protocol Example

Let's start with a simple class that defines a __pprint__() method:

class Bass:
    def __init__(self, strings: int, pickups: str, active: bool=False):
        self._strings = strings
        self._pickups = pickups
        self._active = active

    def __pprint__(self):
        yield self._strings
        yield 'pickups', self._pickups
        yield 'active', self._active, False

precision = Bass(4, 'split coil P', active=False)
stingray = Bass(5, 'humbucker', active=True)

The __pprint__() method yields three values, which correspond to the __init__() arguments, showing by example each of the three different allowed formats. Here is what the output looks like:

>>> pprint.pprint(precision)
Bass(4, pickups='split coil P')
>>> pprint.pprint(stingray)
Bass(5, pickups='humbucker', active=True)

Note that you'd get exactly the same output if you used print(..., pretty=True).