mirror of https://github.com/python/cpython
294 lines
12 KiB
ReStructuredText
294 lines
12 KiB
ReStructuredText
:mod:`pprint` --- Data pretty printer
|
|
=====================================
|
|
|
|
.. module:: pprint
|
|
:synopsis: Data pretty printer.
|
|
.. moduleauthor:: Fred L. Drake, Jr. <fdrake@acm.org>
|
|
.. sectionauthor:: Fred L. Drake, Jr. <fdrake@acm.org>
|
|
|
|
**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, classes, or instances are included, as well as many
|
|
other built-in objects which are not representable as Python constants.
|
|
|
|
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.
|
|
Construct :class:`PrettyPrinter` objects explicitly if you need to adjust the
|
|
width constraint.
|
|
|
|
Dictionaries are sorted by key before the display is computed.
|
|
|
|
The :mod:`pprint` module defines one class:
|
|
|
|
.. First the implementation class:
|
|
|
|
|
|
.. class:: PrettyPrinter(indent=1, width=80, depth=None, stream=None)
|
|
|
|
Construct a :class:`PrettyPrinter` instance. This constructor understands
|
|
several keyword parameters. An output stream may be set using the *stream*
|
|
keyword; the only method used on the stream object is the file protocol's
|
|
:meth:`write` method. If not specified, the :class:`PrettyPrinter` adopts
|
|
``sys.stdout``. Three additional parameters may be used to control the
|
|
formatted representation. The keywords are *indent*, *depth*, and *width*. The
|
|
amount of indentation added for each recursive level is specified by *indent*;
|
|
the default is one. Other values can cause output to look a little odd, but can
|
|
make nesting easier to spot. The number of levels which may be printed is
|
|
controlled by *depth*; if the data structure being printed is too deep, the next
|
|
contained level is replaced by ``...``. By default, there is no constraint on
|
|
the depth of the objects being formatted. The desired output width is
|
|
constrained using the *width* parameter; the default is 80 characters. If a
|
|
structure cannot be formatted within the constrained width, a best effort will
|
|
be made.
|
|
|
|
>>> 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']
|
|
>>> tup = ('spam', ('eggs', ('lumberjack', ('knights', ('ni', ('dead',
|
|
... ('parrot', ('fresh fruit',))))))))
|
|
>>> pp = pprint.PrettyPrinter(depth=6)
|
|
>>> pp.pprint(tup)
|
|
('spam', ('eggs', ('lumberjack', ('knights', ('ni', ('dead', (...)))))))
|
|
|
|
|
|
The :class:`PrettyPrinter` class supports several derivative functions:
|
|
|
|
.. function:: pformat(object, indent=1, width=80, depth=None)
|
|
|
|
Return the formatted representation of *object* as a string. *indent*, *width*
|
|
and *depth* will be passed to the :class:`PrettyPrinter` constructor as
|
|
formatting parameters.
|
|
|
|
|
|
.. function:: pprint(object, stream=None, indent=1, width=80, depth=None)
|
|
|
|
Prints the formatted representation of *object* on *stream*, followed by a
|
|
newline. If *stream* is ``None``, ``sys.stdout`` is used. This may be used
|
|
in the interactive interpreter instead of the :func:`print` function for
|
|
inspecting values (you can even reassign ``print = pprint.pprint`` for use
|
|
within a scope). *indent*, *width* and *depth* will be passed to the
|
|
:class:`PrettyPrinter` constructor as formatting parameters.
|
|
|
|
>>> import pprint
|
|
>>> stuff = ['spam', 'eggs', 'lumberjack', 'knights', 'ni']
|
|
>>> stuff.insert(0, stuff)
|
|
>>> pprint.pprint(stuff)
|
|
[<Recursion on list with id=...>,
|
|
'spam',
|
|
'eggs',
|
|
'lumberjack',
|
|
'knights',
|
|
'ni']
|
|
|
|
|
|
.. function:: isreadable(object)
|
|
|
|
.. index:: builtin: 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.
|
|
|
|
|
|
One more support function is also defined:
|
|
|
|
.. function:: saferepr(object)
|
|
|
|
Return a string representation of *object*, protected against recursive data
|
|
structures. 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
|
|
---------------------
|
|
|
|
: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:: builtin: 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` function and its parameters,
|
|
let's fetch information about a package from PyPI::
|
|
|
|
>>> import json
|
|
>>> import pprint
|
|
>>> from urllib.request import urlopen
|
|
>>> with urlopen('http://pypi.python.org/pypi/configparser/json') as url:
|
|
... http_info = url.info()
|
|
... raw_data = url.read().decode(http_info.get_content_charset())
|
|
>>> package_data = json.loads(raw_data)
|
|
>>> result = {'headers': http_info.items(), 'body': package_data}
|
|
|
|
In its basic form, :func:`pprint` shows the whole object::
|
|
|
|
>>> pprint.pprint(result)
|
|
{'body': {'info': {'_pypi_hidden': False,
|
|
'_pypi_ordering': 12,
|
|
'classifiers': ['Development Status :: 4 - Beta',
|
|
'Intended Audience :: Developers',
|
|
'License :: OSI Approved :: MIT License',
|
|
'Natural Language :: English',
|
|
'Operating System :: OS Independent',
|
|
'Programming Language :: Python',
|
|
'Programming Language :: Python :: 2',
|
|
'Programming Language :: Python :: 2.6',
|
|
'Programming Language :: Python :: 2.7',
|
|
'Topic :: Software Development :: Libraries',
|
|
'Topic :: Software Development :: Libraries :: Python Modules'],
|
|
'download_url': 'UNKNOWN',
|
|
'home_page': 'http://docs.python.org/py3k/library/configparser.html',
|
|
'keywords': 'configparser ini parsing conf cfg configuration file',
|
|
'license': 'MIT',
|
|
'name': 'configparser',
|
|
'package_url': 'http://pypi.python.org/pypi/configparser',
|
|
'platform': 'any',
|
|
'release_url': 'http://pypi.python.org/pypi/configparser/3.2.0r3',
|
|
'requires_python': None,
|
|
'stable_version': None,
|
|
'summary': 'This library brings the updated configparser from Python 3.2+ to Python 2.6-2.7.',
|
|
'version': '3.2.0r3'},
|
|
'urls': [{'comment_text': '',
|
|
'downloads': 47,
|
|
'filename': 'configparser-3.2.0r3.tar.gz',
|
|
'has_sig': False,
|
|
'md5_digest': '8500fd87c61ac0de328fc996fce69b96',
|
|
'packagetype': 'sdist',
|
|
'python_version': 'source',
|
|
'size': 32281,
|
|
'upload_time': '2011-05-10T16:28:50',
|
|
'url': 'http://pypi.python.org/packages/source/c/configparser/configparser-3.2.0r3.tar.gz'}]},
|
|
'headers': [('Date', 'Sat, 14 May 2011 12:48:52 GMT'),
|
|
('Server', 'Apache/2.2.16 (Debian)'),
|
|
('Content-Disposition', 'inline'),
|
|
('Connection', 'close'),
|
|
('Transfer-Encoding', 'chunked'),
|
|
('Content-Type', 'application/json; charset="UTF-8"')]}
|
|
|
|
The result can be limited to a certain *depth* (ellipsis is used for deeper
|
|
contents)::
|
|
|
|
>>> pprint.pprint(result, depth=3)
|
|
{'body': {'info': {'_pypi_hidden': False,
|
|
'_pypi_ordering': 12,
|
|
'classifiers': [...],
|
|
'download_url': 'UNKNOWN',
|
|
'home_page': 'http://docs.python.org/py3k/library/configparser.html',
|
|
'keywords': 'configparser ini parsing conf cfg configuration file',
|
|
'license': 'MIT',
|
|
'name': 'configparser',
|
|
'package_url': 'http://pypi.python.org/pypi/configparser',
|
|
'platform': 'any',
|
|
'release_url': 'http://pypi.python.org/pypi/configparser/3.2.0r3',
|
|
'requires_python': None,
|
|
'stable_version': None,
|
|
'summary': 'This library brings the updated configparser from Python 3.2+ to Python 2.6-2.7.',
|
|
'version': '3.2.0r3'},
|
|
'urls': [{...}]},
|
|
'headers': [('Date', 'Sat, 14 May 2011 12:48:52 GMT'),
|
|
('Server', 'Apache/2.2.16 (Debian)'),
|
|
('Content-Disposition', 'inline'),
|
|
('Connection', 'close'),
|
|
('Transfer-Encoding', 'chunked'),
|
|
('Content-Type', 'application/json; charset="UTF-8"')]}
|
|
|
|
Additionally, maximum *width* can be suggested. If a long object cannot be
|
|
split, the specified width will be exceeded::
|
|
|
|
>>> pprint.pprint(result['headers'], width=30)
|
|
[('Date',
|
|
'Sat, 14 May 2011 12:48:52 GMT'),
|
|
('Server',
|
|
'Apache/2.2.16 (Debian)'),
|
|
('Content-Disposition',
|
|
'inline'),
|
|
('Connection', 'close'),
|
|
('Transfer-Encoding',
|
|
'chunked'),
|
|
('Content-Type',
|
|
'application/json; charset="UTF-8"')]
|