duplicate keys in python dictionary

>>> class Foo(object):
...     pass
...
>>> myfoo=Foo()
>>> myfoo.url="google.com"
>>> mydict={myfoo:"myfoo all up in there"}
>>>
>>> def new_hash(self):
...     return hash(self.url)
...
>>> Foo.__hash__=new_hash
>>>
>>> mydict[myfoo]="myfoo all up in there again!!!"
>>> mydict
{<__main__.Foo object at 0x1050e8cd0>: 'myfoo all up in there again!!!', <__main__.Foo object at 0x1050e8cd0>: 'myfoo all up in there'}