Edit File: pprint.txt
: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. .. versionchanged:: 2.5 Dictionaries are sorted by key before the display is computed; before 2.5, a dictionary was sorted only if its display required more than one line, although that wasn't documented. .. versionchanged:: 2.6 Added support for :class:`set` and :class:`frozenset`. 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. .. versionchanged:: 2.4 The parameters *indent*, *width* and *depth* were added. .. 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 a :keyword:`print` statement for inspecting values. *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'] .. versionchanged:: 2.4 The parameters *indent*, *width* and *depth* were added. .. 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. .. versionadded:: 2.3 .. _pprint-example: 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']]