Is it worth clarifying that __init__ can return a value but only the value None? The following won't raise a TypeError:

class O(object):
    def __init__(self):
        return None

Admittedly the "return None" is the default behaviour but people may attempt this in order to "block creation" of the instance (as __new__ is less well-known, I have seen the above attempted on Stack Overflow: http://stackoverflow.com/questions/26896941/proper-way-to-terminate-object-creation-inside-of-init/)