Doc/library/pprint.rst
!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.
.. _pprint-functions:
.. function:: pp(object, stream=None, indent=1, width=80, depth=None, *,
compact=False, expand=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.
Incompatible with expand.
:param bool expand:
If True,
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. Incompatible with compact.
: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, expand=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, expand=False, sort_dicts=True,
underscore_numbers=False)
Return the formatted representation of object as a string. indent,
width, depth, compact, expand, 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(indent=1, width=80, depth=None, stream=None, *,
compact=False, expand=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(indent=4) pp.pprint(stuff) [ ['spam', 'eggs', 'lumberjack', 'knights', 'ni'], 'spam', 'eggs', 'lumberjack', 'knights', 'ni'] pp = pprint.PrettyPrinter(width=41, compact=True) pp.pprint(stuff) [['spam', 'eggs', 'lumberjack', 'knights', 'ni'], 'spam', 'eggs', 'lumberjack', 'knights', 'ni'] pp = pprint.PrettyPrinter(width=41, expand=True, 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 Added the expand parameter.
: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:
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': '[email protected]', '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': '[email protected]', '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': '[email protected]', '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'}
Lastly, we can format like pretty-printed JSON with the expand parameter. Best results are achieved with a higher indent value::
pprint.pp(project_info, indent=4, expand=True) { 'author': 'The Python Packaging Authority', 'author_email': '[email protected]', '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}, 'dynamic': None, 'home_page': 'https://github.com/pypa/sampleproject', 'keywords': 'sample setuptools development', 'license': 'MIT', 'license_expression': None, 'license_files': None, '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', }, 'provides_extra': None, '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', 'yanked': False, 'yanked_reason': None, }