Mastering Python

lambda functions

The lambda statement in Python is simply an anonymous function. Due to the syntax, it is slightly more limited than regular functions, but a lot can be done through it. As always though, readability counts, so generally it is a good idea to keep it as simple as possible. One of the more common use cases is the sort key for the sorted function:

>>> class Spam(object):
...     def __init__(self, value):
...         self.value = value
...
...     def __repr__(self):
...         return '<%s: %s>' % (self.__class__.__name__, self.value)
...
>>> spams = [Spam(5), Spam(2), Spam(4), Spam(1)]
>>> sorted_spams = sorted(spams, key=lambda spam: spam.value)
>>> spams
[<Spam: 5>, <Spam: 2>, <Spam: 4>, <Spam: 1>]
>>> sorted_spams
[<Spam: 1>, <Spam: 2>, <Spam: 4>, <Spam: ...