2 :mod:`pprint` --- Data pretty printer
3 =====================================
6 :synopsis: Data pretty printer.
7 .. moduleauthor:: Fred L. Drake, Jr. <fdrake@acm.org>
8 .. sectionauthor:: Fred L. Drake, Jr. <fdrake@acm.org>
11 The :mod:`pprint` module provides a capability to "pretty-print" arbitrary
12 Python data structures in a form which can be used as input to the interpreter.
13 If the formatted structures include objects which are not fundamental Python
14 types, the representation may not be loadable. This may be the case if objects
15 such as files, sockets, classes, or instances are included, as well as many
16 other builtin objects which are not representable as Python constants.
18 The formatted representation keeps objects on a single line if it can, and
19 breaks them onto multiple lines if they don't fit within the allowed width.
20 Construct :class:`PrettyPrinter` objects explicitly if you need to adjust the
23 .. versionchanged:: 2.5
24 Dictionaries are sorted by key before the display is computed; before 2.5, a
25 dictionary was sorted only if its display required more than one line, although
26 that wasn't documented.
28 .. versionchanged:: 2.6
29 Added support for :class:`set` and :class:`frozenset`.
31 The :mod:`pprint` module defines one class:
33 .. First the implementation class:
36 .. class:: PrettyPrinter(...)
38 Construct a :class:`PrettyPrinter` instance. This constructor understands
39 several keyword parameters. An output stream may be set using the *stream*
40 keyword; the only method used on the stream object is the file protocol's
41 :meth:`write` method. If not specified, the :class:`PrettyPrinter` adopts
42 ``sys.stdout``. Three additional parameters may be used to control the
43 formatted representation. The keywords are *indent*, *depth*, and *width*. The
44 amount of indentation added for each recursive level is specified by *indent*;
45 the default is one. Other values can cause output to look a little odd, but can
46 make nesting easier to spot. The number of levels which may be printed is
47 controlled by *depth*; if the data structure being printed is too deep, the next
48 contained level is replaced by ``...``. By default, there is no constraint on
49 the depth of the objects being formatted. The desired output width is
50 constrained using the *width* parameter; the default is 80 characters. If a
51 structure cannot be formatted within the constrained width, a best effort will
55 >>> stuff = ['spam', 'eggs', 'lumberjack', 'knights', 'ni']
56 >>> stuff.insert(0, stuff[:])
57 >>> pp = pprint.PrettyPrinter(indent=4)
59 [ ['spam', 'eggs', 'lumberjack', 'knights', 'ni'],
65 >>> tup = ('spam', ('eggs', ('lumberjack', ('knights', ('ni', ('dead',
66 ... ('parrot', ('fresh fruit',))))))))
67 >>> pp = pprint.PrettyPrinter(depth=6)
69 ('spam', ('eggs', ('lumberjack', ('knights', ('ni', ('dead', (...)))))))
71 The :class:`PrettyPrinter` class supports several derivative functions:
73 .. Now the derivative functions:
75 .. function:: pformat(object[, indent[, width[, depth]]])
77 Return the formatted representation of *object* as a string. *indent*, *width*
78 and *depth* will be passed to the :class:`PrettyPrinter` constructor as
79 formatting parameters.
81 .. versionchanged:: 2.4
82 The parameters *indent*, *width* and *depth* were added.
85 .. function:: pprint(object[, stream[, indent[, width[, depth]]]])
87 Prints the formatted representation of *object* on *stream*, followed by a
88 newline. If *stream* is omitted, ``sys.stdout`` is used. This may be used in
89 the interactive interpreter instead of a :keyword:`print` statement for
90 inspecting values. *indent*, *width* and *depth* will be passed to the
91 :class:`PrettyPrinter` constructor as formatting parameters.
94 >>> stuff = ['spam', 'eggs', 'lumberjack', 'knights', 'ni']
95 >>> stuff.insert(0, stuff)
96 >>> pprint.pprint(stuff)
97 [<Recursion on list with id=...>,
104 .. versionchanged:: 2.4
105 The parameters *indent*, *width* and *depth* were added.
108 .. function:: isreadable(object)
110 .. index:: builtin: eval
112 Determine if the formatted representation of *object* is "readable," or can be
113 used to reconstruct the value using :func:`eval`. This always returns ``False``
114 for recursive objects.
116 >>> pprint.isreadable(stuff)
120 .. function:: isrecursive(object)
122 Determine if *object* requires a recursive representation.
125 One more support function is also defined:
127 .. function:: saferepr(object)
129 Return a string representation of *object*, protected against recursive data
130 structures. If the representation of *object* exposes a recursive entry, the
131 recursive reference will be represented as ``<Recursion on typename with
132 id=number>``. The representation is not otherwise formatted.
134 >>> pprint.saferepr(stuff)
135 "[<Recursion on list with id=...>, 'spam', 'eggs', 'lumberjack', 'knights', 'ni']"
138 .. _prettyprinter-objects:
140 PrettyPrinter Objects
141 ---------------------
143 :class:`PrettyPrinter` instances have the following methods:
146 .. method:: PrettyPrinter.pformat(object)
148 Return the formatted representation of *object*. This takes into account the
149 options passed to the :class:`PrettyPrinter` constructor.
152 .. method:: PrettyPrinter.pprint(object)
154 Print the formatted representation of *object* on the configured stream,
155 followed by a newline.
157 The following methods provide the implementations for the corresponding
158 functions of the same names. Using these methods on an instance is slightly
159 more efficient since new :class:`PrettyPrinter` objects don't need to be
163 .. method:: PrettyPrinter.isreadable(object)
165 .. index:: builtin: eval
167 Determine if the formatted representation of the object is "readable," or can be
168 used to reconstruct the value using :func:`eval`. Note that this returns
169 ``False`` for recursive objects. If the *depth* parameter of the
170 :class:`PrettyPrinter` is set and the object is deeper than allowed, this
174 .. method:: PrettyPrinter.isrecursive(object)
176 Determine if the object requires a recursive representation.
178 This method is provided as a hook to allow subclasses to modify the way objects
179 are converted to strings. The default implementation uses the internals of the
180 :func:`saferepr` implementation.
183 .. method:: PrettyPrinter.format(object, context, maxlevels, level)
185 Returns three values: the formatted version of *object* as a string, a flag
186 indicating whether the result is readable, and a flag indicating whether
187 recursion was detected. The first argument is the object to be presented. The
188 second is a dictionary which contains the :func:`id` of objects that are part of
189 the current presentation context (direct and indirect containers for *object*
190 that are affecting the presentation) as the keys; if an object needs to be
191 presented which is already represented in *context*, the third return value
192 should be ``True``. Recursive calls to the :meth:`format` method should add
193 additional entries for containers to this dictionary. The third argument,
194 *maxlevels*, gives the requested limit to recursion; this will be ``0`` if there
195 is no requested limit. This argument should be passed unmodified to recursive
196 calls. The fourth argument, *level*, gives the current level; recursive calls
197 should be passed a value less than that of the current call.
199 .. versionadded:: 2.3
206 This example demonstrates several uses of the :func:`pprint` function and its parameters.
209 >>> tup = ('spam', ('eggs', ('lumberjack', ('knights', ('ni', ('dead',
210 ... ('parrot', ('fresh fruit',))))))))
211 >>> stuff = ['a' * 10, tup, ['a' * 30, 'b' * 30], ['c' * 20, 'd' * 20]]
212 >>> pprint.pprint(stuff)
217 ('knights', ('ni', ('dead', ('parrot', ('fresh fruit',)))))))),
218 ['aaaaaaaaaaaaaaaaaaaaaaaaaaaaaa', 'bbbbbbbbbbbbbbbbbbbbbbbbbbbbbb'],
219 ['cccccccccccccccccccc', 'dddddddddddddddddddd']]
220 >>> pprint.pprint(stuff, depth=3)
222 ('spam', ('eggs', (...))),
223 ['aaaaaaaaaaaaaaaaaaaaaaaaaaaaaa', 'bbbbbbbbbbbbbbbbbbbbbbbbbbbbbb'],
224 ['cccccccccccccccccccc', 'dddddddddddddddddddd']]
225 >>> pprint.pprint(stuff, width=60)
231 ('ni', ('dead', ('parrot', ('fresh fruit',)))))))),
232 ['aaaaaaaaaaaaaaaaaaaaaaaaaaaaaa',
233 'bbbbbbbbbbbbbbbbbbbbbbbbbbbbbb'],
234 ['cccccccccccccccccccc', 'dddddddddddddddddddd']]