3.20 pprint -- Data pretty printer
Keywords: lib

# 3.20 `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.

The `pprint` module defines one 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)
  Return the formatted representation of object as a string. The default parameters for formatting are used.

`pprint` (object[, stream])
  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. The default parameters for formatting are used.

        >>> 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']

`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)
        0

`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']"

Subsections

- 3.20.1 PrettyPrinter Objects