invalid-length-hint-returned.md

Pattern: __length_hint__ does not return non-negative integer

Issue: -

Description

Used when a __length_hint__ method returns something which is not a non-negative integer.

Example of incorrect code:

class BadLengthHint(object):
    """ __length_hint__ returns a negative integer """

    def __length_hint__(self):  # [invalid-length-hint-returned]
        return -1

Example of correct code:

class GoodLengthHint(object):
    """__length_hint__ returns <type 'int'>"""

    def __length_hint__(self):
        return 0