IPython.lib.pretty

Python advanced pretty printer. This pretty printer is intended to replace the old pprint python module which does not allow developers to provide their own pretty print callbacks.

This module is based on ruby's prettyprint.rb library by Tanaka Akira.

Example Usage

To directly print the representation of an object use pprint:

from pretty import pprint
pprint(complex_object)

To get a string of the output use pretty:

from pretty import pretty
string = pretty(complex_object)

Extending

The pretty library allows developers to add pretty printing rules for their own objects. This process is straightforward. All you have to do is to add a _repr_pretty_ method to your object and call the methods on the pretty printer passed

class MyObject(object):

    def _repr_pretty_(self, p, cycle):
        ...

Here's an example for a class with a simple constructor

class MySimpleObject:

    def __init__(self, a, b, *, c=None):
        self.a = a
        self.b = b
        self.c = c

    def _repr_pretty_(self, p, cycle):
        ctor = CallExpression.factory(self.__class__.__name__)
        if self.c is None:
            p.pretty(ctor(a, b))
        else:
            p.pretty(ctor(a, b, c=c))

Here is an example implementation of a _repr_pretty_ method for a list subclass

class MyList(list):

    def _repr_pretty_(self, p, cycle):
        if cycle:
            p.text('MyList(...)')
        else:
            with p.group(8, 'MyList([', '])'):
                for idx, item in enumerate(self):
                    if idx:
                        p.text(',')
                        p.breakable()
                    p.pretty(item)

The cycle parameter is True if pretty detected a cycle. You have to react to that or the result is an infinite loop. p.text() just adds non breaking text to the output, p.breakable() either adds a whitespace or breaks here. If you pass it an argument it's used instead of the default space. p.pretty prettyprints another object using the pretty print method.

The first parameter to the group function specifies the extra indentation of the next line. In this example the next item will either be on the same line (if the items are short enough) or aligned with the right edge of the opening bracket of MyList.

If you just want to indent something you can use the group function without open / close parameters. You can also use this code

with p.indent(2):
    ...

Inheritance diagram:

copyright

2007 by Armin Ronacher. Portions (c) 2009 by Robert Kern.

license

BSD License.