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sandbox/antoine / Doc / library / pprint.rst

:mod:`pprint` --- 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, 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.

The :mod:`pprint` module defines one class:

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:

One more support function is also defined:

PrettyPrinter Objects

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

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.

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.

pprint Example

This example demonstrates several uses of the :func:`pprint` function and its parameters.

>>> import pprint
>>> tup = ('spam', ('eggs', ('lumberjack', ('knights', ('ni', ('dead',
... ('parrot', ('fresh fruit',))))))))
>>> stuff = ['a' * 10, tup, ['a' * 30, 'b' * 30], ['c' * 20, 'd' * 20]]
>>> pprint.pprint(stuff)
['aaaaaaaaaa',
 ('spam',
  ('eggs',
   ('lumberjack',
    ('knights', ('ni', ('dead', ('parrot', ('fresh fruit',)))))))),
 ['aaaaaaaaaaaaaaaaaaaaaaaaaaaaaa', 'bbbbbbbbbbbbbbbbbbbbbbbbbbbbbb'],
 ['cccccccccccccccccccc', 'dddddddddddddddddddd']]
>>> pprint.pprint(stuff, depth=3)
['aaaaaaaaaa',
 ('spam', ('eggs', (...))),
 ['aaaaaaaaaaaaaaaaaaaaaaaaaaaaaa', 'bbbbbbbbbbbbbbbbbbbbbbbbbbbbbb'],
 ['cccccccccccccccccccc', 'dddddddddddddddddddd']]
>>> pprint.pprint(stuff, width=60)
['aaaaaaaaaa',
 ('spam',
  ('eggs',
   ('lumberjack',
    ('knights',
     ('ni', ('dead', ('parrot', ('fresh fruit',)))))))),
 ['aaaaaaaaaaaaaaaaaaaaaaaaaaaaaa',
  'bbbbbbbbbbbbbbbbbbbbbbbbbbbbbb'],
 ['cccccccccccccccccccc', 'dddddddddddddddddddd']]