In [138]: class bad(object):
    def __init__(self, str):
        self._str = str
    def __repr__(self):
        return repr(self._str)
    def __hash__(self):
        return 1
   .....: 

In [145]: set([bad("cat"), bad("dog"), bad("fish")])
Out[145]: set(['cat', 'fish', 'dog'])

In [146]: [hash(i) for i in set([bad("cat"), bad("dog"), bad("fish")])]
Out[146]: [1, 1, 1]