Python in a Nutshell

Name

__len__

Synopsis

__len__(self)

The len( x ) built-in function call, and other built-in functions that need to know how many items are in container x, call x .__len__( ). __len__ should return an int, the number of items in x. Python also calls x .__len__( ) to evaluate x in a Boolean context, if __nonzero__ is absent. Absent __nonzero__, a container is taken as false if and only if the container is empty (i.e., the container’s length is 0).