5.18 pprint -- Data pretty printer

5.18 `pprint` -- Data pretty printer

The 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 PrettyPrinter objects explicitly if you need to adjust the width constraint.

Changed in version 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 pprint module defines one class:

class PrettyPrinter( ...)

Construct a 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 write() method. If not specified, the 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 eighty 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 PrettyPrinter class supports several derivative functions:

pformat( object[, indent[, width[, depth]]]): Return the formatted representation of object as a string. indent, width and depth will be passed to the PrettyPrinter constructor as formatting parameters. Changed in version 2.4: The parameters indent, width and depth were added.

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 print statement for inspecting values. indent, width and depth will be passed to the 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']

Changed in version 2.4: The parameters indent, width and depth were added.

isreadable( object)

Determine if the formatted representation of object is ``readable,'' or can be used to reconstruct the value using eval(). This always returns false for recursive objects.

>>> pprint.isreadable(stuff)
False

isrecursive( object): Determine if object requires a recursive representation.

One more support function is also defined:

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=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']"

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