7.12. pprint
— Data pretty printer¶
Source code: Lib/pprint.py
The 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 PrettyPrinter
objects explicitly if you need to adjust the
width constraint.
Dictionaries are sorted by key before the display is computed.
The pprint
module defines one class:
-
class
pprint.
PrettyPrinter
(indent=1, width=80, depth=None, stream=None)¶ Construct a
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’swrite()
method. If not specified, thePrettyPrinter
adoptssys.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 PrettyPrinter
class supports several derivative functions:
-
pprint.
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
PrettyPrinter
constructor as formatting parameters.
-
pprint.
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 theprint()
function for inspecting values (you can even reassignprint = pprint.pprint
for use within a scope). indent, width and depth will be passed to thePrettyPrinter
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']
-
pprint.
isreadable
(object)¶ Determine if the formatted representation of object is “readable,” or can be used to reconstruct the value using
eval()
. This always returnsFalse
for recursive objects.>>> pprint.isreadable(stuff) False
-
pprint.
isrecursive
(object)¶ Determine if object requires a recursive representation.
One more support function is also defined:
-
pprint.
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']"
7.12.1. PrettyPrinter Objects¶
PrettyPrinter
instances have the following methods:
-
PrettyPrinter.
pformat
(object)¶ Return the formatted representation of object. This takes into account the options passed to the
PrettyPrinter
constructor.
-
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 PrettyPrinter
objects don’t need to be
created.
-
PrettyPrinter.
isreadable
(object)¶ Determine if the formatted representation of the object is “readable,” or can be used to reconstruct the value using
eval()
. Note that this returnsFalse
for recursive objects. If the depth parameter of thePrettyPrinter
is set and the object is deeper than allowed, this returnsFalse
.
-
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
saferepr()
implementation.
-
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
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 beTrue
. Recursive calls to theformat()
method should add additional entries for containers to this dictionary. The third argument, maxlevels, gives the requested limit to recursion; this will be0
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.
7.12.2. Example¶
To demonstrate several uses of the pprint()
function and its parameters,
let’s fetch information about a project 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())
>>> project_info = json.loads(raw_data)
>>> result = {'headers': http_info.items(), 'body': project_info}
In its basic form, 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"')]