Purpose of __repr__ method?

def __repr__(self):
  return '<%s %s (%s:%s) %s>' % (
    self.__class__.__name__, self.urlconf_name, self.app_name,
    self.namespace, self.regex.pattern)

What is the significance/purpose of this method?

Solution 1:

__repr__ should return a printable representation of the object, most likely one of the ways possible to create this object. See official documentation here. __repr__ is more for developers while __str__ is for end users.

A simple example:

>>> class Point:
...   def __init__(self, x, y):
...     self.x, self.y = x, y
...   def __repr__(self):
...     return 'Point(x=%s, y=%s)' % (self.x, self.y)
>>> p = Point(1, 2)
>>> p
Point(x=1, y=2)

Solution 2:

This is explained quite well in the Python documentation:

repr(object): Return a string containing a printable representation of an object. This is the same value yielded by conversions (reverse quotes). It is sometimes useful to be able to access this operation as an ordinary function. For many types, this function makes an attempt to return a string that would yield an object with the same value when passed to eval(), otherwise the representation is a string enclosed in angle brackets that contains the name of the type of the object together with additional information often including the name and address of the object. A class can control what this function returns for its instances by defining a __repr__() method.

So what you're seeing here is the default implementation of __repr__, which is useful for serialization and debugging.

Solution 3:

__repr__ is used by the standalone Python interpreter to display a class in printable format. Example:

~> python3.5
Python 3.5.1 (v3.5.1:37a07cee5969, Dec  5 2015, 21:12:44) 
[GCC 4.2.1 (Apple Inc. build 5666) (dot 3)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> class StackOverflowDemo:
...     def __init__(self):
...         pass
...     def __repr__(self):
...         return '<StackOverflow demo object __repr__>'
... 
>>> demo = StackOverflowDemo()
>>> demo
<StackOverflow demo object __repr__>

In cases where a __str__ method is not defined in the class, it will call the __repr__ function in an attempt to create a printable representation.

>>> str(demo)
'<StackOverflow demo object __repr__>'

Additionally, print()ing the class will call __str__ by default.

Documentation, if you please