mirror of https://github.com/python/cpython
203 lines
7.9 KiB
ReStructuredText
203 lines
7.9 KiB
ReStructuredText
|
|
: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.
|
|
|
|
Dictionaries are sorted by key before the display is computed.
|
|
|
|
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.
|
|
|
|
|
|
.. 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 the :func:`print` function for
|
|
inspecting values (you can even reassign ``print = pprint.pprint`` for use
|
|
within a scope). *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']
|
|
|
|
|
|
.. 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.
|