non-iterator-returned.md

Pattern: Return iterator in __iter__

Issue: -

Description

Used when an __iter__ method returns something which is not an iterable (i.e. has no next method). A container must implement an __iter__ method that returns an iterator object, otherwise Python will raise the TypeError: __iter__ returned non-iterator of type %r.

Example of incorrect code:

class GoodIterator(object):
    """ yields in iterator. """

    def __iter__(self):
        for index in range(10):
            yield index

Example of correct code:

class BadIterator(object):
    """ __iter__ returns a list """

    def __iter__(self): # [non-iterator-returned]
        return []

Further Reading

• The Python Standard Library - Iterator Types