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authorGeorg Brandl <georg@python.org>2007-08-15 14:28:22 +0000
committerGeorg Brandl <georg@python.org>2007-08-15 14:28:22 +0000
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+
+: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>
+
+
+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 builtin 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.
+
+The :mod:`pprint` module defines one class:
+
+.. % First the implementation class:
+
+
+.. class:: PrettyPrinter(...)
+
+ 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, sys
+ >>> stuff = sys.path[:]
+ >>> stuff.insert(0, stuff[:])
+ >>> pp = pprint.PrettyPrinter(indent=4)
+ >>> pp.pprint(stuff)
+ [ [ '',
+ '/usr/local/lib/python1.5',
+ '/usr/local/lib/python1.5/test',
+ '/usr/local/lib/python1.5/sunos5',
+ '/usr/local/lib/python1.5/sharedmodules',
+ '/usr/local/lib/python1.5/tkinter'],
+ '',
+ '/usr/local/lib/python1.5',
+ '/usr/local/lib/python1.5/test',
+ '/usr/local/lib/python1.5/sunos5',
+ '/usr/local/lib/python1.5/sharedmodules',
+ '/usr/local/lib/python1.5/tkinter']
+ >>>
+ >>> import parser
+ >>> tup = parser.ast2tuple(
+ ... parser.suite(open('pprint.py').read()))[1][1][1]
+ >>> pp = pprint.PrettyPrinter(depth=6)
+ >>> pp.pprint(tup)
+ (266, (267, (307, (287, (288, (...))))))
+
+The :class:`PrettyPrinter` class supports several derivative functions:
+
+.. % Now the derivative functions:
+
+
+.. function:: pformat(object[, indent[, width[, depth]]])
+
+ 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[, indent[, width[, depth]]]])
+
+ Prints the formatted representation of *object* on *stream*, followed by a
+ newline. If *stream* is omitted, ``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. ::
+
+ >>> stuff = sys.path[:]
+ >>> stuff.insert(0, stuff)
+ >>> pprint.pprint(stuff)
+ [<Recursion on list with id=869440>,
+ '',
+ '/usr/local/lib/python1.5',
+ '/usr/local/lib/python1.5/test',
+ '/usr/local/lib/python1.5/sunos5',
+ '/usr/local/lib/python1.5/sharedmodules',
+ '/usr/local/lib/python1.5/tkinter']
+
+ .. 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.
+
+.. % This example is outside the {funcdesc} to keep it from running over
+.. % the right margin.
+
+::
+
+ >>> pprint.saferepr(stuff)
+ "[<Recursion on list with id=682968>, '', '/usr/local/lib/python1.5', '/usr/loca
+ l/lib/python1.5/test', '/usr/local/lib/python1.5/sunos5', '/usr/local/lib/python
+ 1.5/sharedmodules', '/usr/local/lib/python1.5/tkinter']"
+
+
+.. _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
+