1 :mod:`pprint` --- Data pretty printer 2 ===================================== 3 4 .. module:: pprint 5 :synopsis: Data pretty printer. 6 .. moduleauthor:: Fred L. Drake, Jr. <fdrake (a] acm.org> 7 .. sectionauthor:: Fred L. Drake, Jr. <fdrake (a] acm.org> 8 9 **Source code:** :source:`Lib/pprint.py` 10 11 -------------- 12 13 The :mod:`pprint` module provides a capability to "pretty-print" arbitrary 14 Python data structures in a form which can be used as input to the interpreter. 15 If the formatted structures include objects which are not fundamental Python 16 types, the representation may not be loadable. This may be the case if objects 17 such as files, sockets, classes, or instances are included, as well as many 18 other built-in objects which are not representable as Python constants. 19 20 The formatted representation keeps objects on a single line if it can, and 21 breaks them onto multiple lines if they don't fit within the allowed width. 22 Construct :class:`PrettyPrinter` objects explicitly if you need to adjust the 23 width constraint. 24 25 .. versionchanged:: 2.5 26 Dictionaries are sorted by key before the display is computed; before 2.5, a 27 dictionary was sorted only if its display required more than one line, although 28 that wasn't documented. 29 30 .. versionchanged:: 2.6 31 Added support for :class:`set` and :class:`frozenset`. 32 33 34 The :mod:`pprint` module defines one class: 35 36 .. First the implementation class: 37 38 39 .. class:: PrettyPrinter(indent=1, width=80, depth=None, stream=None) 40 41 Construct a :class:`PrettyPrinter` instance. This constructor understands 42 several keyword parameters. An output stream may be set using the *stream* 43 keyword; the only method used on the stream object is the file protocol's 44 :meth:`write` method. If not specified, the :class:`PrettyPrinter` adopts 45 ``sys.stdout``. Three additional parameters may be used to control the 46 formatted representation. The keywords are *indent*, *depth*, and *width*. The 47 amount of indentation added for each recursive level is specified by *indent*; 48 the default is one. Other values can cause output to look a little odd, but can 49 make nesting easier to spot. The number of levels which may be printed is 50 controlled by *depth*; if the data structure being printed is too deep, the next 51 contained level is replaced by ``...``. By default, there is no constraint on 52 the depth of the objects being formatted. The desired output width is 53 constrained using the *width* parameter; the default is 80 characters. If a 54 structure cannot be formatted within the constrained width, a best effort will 55 be made. 56 57 >>> import pprint 58 >>> stuff = ['spam', 'eggs', 'lumberjack', 'knights', 'ni'] 59 >>> stuff.insert(0, stuff[:]) 60 >>> pp = pprint.PrettyPrinter(indent=4) 61 >>> pp.pprint(stuff) 62 [ ['spam', 'eggs', 'lumberjack', 'knights', 'ni'], 63 'spam', 64 'eggs', 65 'lumberjack', 66 'knights', 67 'ni'] 68 >>> tup = ('spam', ('eggs', ('lumberjack', ('knights', ('ni', ('dead', 69 ... ('parrot', ('fresh fruit',)))))))) 70 >>> pp = pprint.PrettyPrinter(depth=6) 71 >>> pp.pprint(tup) 72 ('spam', ('eggs', ('lumberjack', ('knights', ('ni', ('dead', (...))))))) 73 74 The :class:`PrettyPrinter` class supports several derivative functions: 75 76 .. function:: pformat(object, indent=1, width=80, depth=None) 77 78 Return the formatted representation of *object* as a string. *indent*, *width* 79 and *depth* will be passed to the :class:`PrettyPrinter` constructor as 80 formatting parameters. 81 82 .. versionchanged:: 2.4 83 The parameters *indent*, *width* and *depth* were added. 84 85 86 .. function:: pprint(object, stream=None, indent=1, width=80, depth=None) 87 88 Prints the formatted representation of *object* on *stream*, followed by a 89 newline. If *stream* is ``None``, ``sys.stdout`` is used. This may be used in 90 the interactive interpreter instead of a :keyword:`print` statement for 91 inspecting values. *indent*, *width* and *depth* will be passed to the 92 :class:`PrettyPrinter` constructor as formatting parameters. 93 94 >>> import pprint 95 >>> stuff = ['spam', 'eggs', 'lumberjack', 'knights', 'ni'] 96 >>> stuff.insert(0, stuff) 97 >>> pprint.pprint(stuff) 98 [<Recursion on list with id=...>, 99 'spam', 100 'eggs', 101 'lumberjack', 102 'knights', 103 'ni'] 104 105 .. versionchanged:: 2.4 106 The parameters *indent*, *width* and *depth* were added. 107 108 109 .. function:: isreadable(object) 110 111 .. index:: builtin: eval 112 113 Determine if the formatted representation of *object* is "readable," or can be 114 used to reconstruct the value using :func:`eval`. This always returns ``False`` 115 for recursive objects. 116 117 >>> pprint.isreadable(stuff) 118 False 119 120 121 .. function:: isrecursive(object) 122 123 Determine if *object* requires a recursive representation. 124 125 126 One more support function is also defined: 127 128 .. function:: saferepr(object) 129 130 Return a string representation of *object*, protected against recursive data 131 structures. If the representation of *object* exposes a recursive entry, the 132 recursive reference will be represented as ``<Recursion on typename with 133 id=number>``. The representation is not otherwise formatted. 134 135 >>> pprint.saferepr(stuff) 136 "[<Recursion on list with id=...>, 'spam', 'eggs', 'lumberjack', 'knights', 'ni']" 137 138 139 .. _prettyprinter-objects: 140 141 PrettyPrinter Objects 142 --------------------- 143 144 :class:`PrettyPrinter` instances have the following methods: 145 146 147 .. method:: PrettyPrinter.pformat(object) 148 149 Return the formatted representation of *object*. This takes into account the 150 options passed to the :class:`PrettyPrinter` constructor. 151 152 153 .. method:: PrettyPrinter.pprint(object) 154 155 Print the formatted representation of *object* on the configured stream, 156 followed by a newline. 157 158 The following methods provide the implementations for the corresponding 159 functions of the same names. Using these methods on an instance is slightly 160 more efficient since new :class:`PrettyPrinter` objects don't need to be 161 created. 162 163 164 .. method:: PrettyPrinter.isreadable(object) 165 166 .. index:: builtin: eval 167 168 Determine if the formatted representation of the object is "readable," or can be 169 used to reconstruct the value using :func:`eval`. Note that this returns 170 ``False`` for recursive objects. If the *depth* parameter of the 171 :class:`PrettyPrinter` is set and the object is deeper than allowed, this 172 returns ``False``. 173 174 175 .. method:: PrettyPrinter.isrecursive(object) 176 177 Determine if the object requires a recursive representation. 178 179 This method is provided as a hook to allow subclasses to modify the way objects 180 are converted to strings. The default implementation uses the internals of the 181 :func:`saferepr` implementation. 182 183 184 .. method:: PrettyPrinter.format(object, context, maxlevels, level) 185 186 Returns three values: the formatted version of *object* as a string, a flag 187 indicating whether the result is readable, and a flag indicating whether 188 recursion was detected. The first argument is the object to be presented. The 189 second is a dictionary which contains the :func:`id` of objects that are part of 190 the current presentation context (direct and indirect containers for *object* 191 that are affecting the presentation) as the keys; if an object needs to be 192 presented which is already represented in *context*, the third return value 193 should be ``True``. Recursive calls to the :meth:`.format` method should add 194 additional entries for containers to this dictionary. The third argument, 195 *maxlevels*, gives the requested limit to recursion; this will be ``0`` if there 196 is no requested limit. This argument should be passed unmodified to recursive 197 calls. The fourth argument, *level*, gives the current level; recursive calls 198 should be passed a value less than that of the current call. 199 200 .. versionadded:: 2.3 201 202 .. _pprint-example: 203 204 pprint Example 205 -------------- 206 207 This example demonstrates several uses of the :func:`pprint` function and its 208 parameters. 209 210 >>> import pprint 211 >>> tup = ('spam', ('eggs', ('lumberjack', ('knights', ('ni', ('dead', 212 ... ('parrot', ('fresh fruit',)))))))) 213 >>> stuff = ['a' * 10, tup, ['a' * 30, 'b' * 30], ['c' * 20, 'd' * 20]] 214 >>> pprint.pprint(stuff) 215 ['aaaaaaaaaa', 216 ('spam', 217 ('eggs', 218 ('lumberjack', 219 ('knights', ('ni', ('dead', ('parrot', ('fresh fruit',)))))))), 220 ['aaaaaaaaaaaaaaaaaaaaaaaaaaaaaa', 'bbbbbbbbbbbbbbbbbbbbbbbbbbbbbb'], 221 ['cccccccccccccccccccc', 'dddddddddddddddddddd']] 222 >>> pprint.pprint(stuff, depth=3) 223 ['aaaaaaaaaa', 224 ('spam', ('eggs', (...))), 225 ['aaaaaaaaaaaaaaaaaaaaaaaaaaaaaa', 'bbbbbbbbbbbbbbbbbbbbbbbbbbbbbb'], 226 ['cccccccccccccccccccc', 'dddddddddddddddddddd']] 227 >>> pprint.pprint(stuff, width=60) 228 ['aaaaaaaaaa', 229 ('spam', 230 ('eggs', 231 ('lumberjack', 232 ('knights', 233 ('ni', ('dead', ('parrot', ('fresh fruit',)))))))), 234 ['aaaaaaaaaaaaaaaaaaaaaaaaaaaaaa', 235 'bbbbbbbbbbbbbbbbbbbbbbbbbbbbbb'], 236 ['cccccccccccccccccccc', 'dddddddddddddddddddd']] 237
