>>> class A(object):
...     def __hash__(self): return 10**100
... 
>>> class B(object):
...     def __hash__(self): return hash(10**100)
...
>>> class C(object):
...     def __hash__(self): return 10
... 
>>> a  = A()
>>> b = B()
>>> c = C()
>>> hash(a) == hash(b)
True
>>> hash(hash(a) ^ hash(c)) == hash(hash(b) ^ hash(c))
True
>>> hash(a.__hash__() ^ c.__hash__()) == hash(b.__hash__() ^ c.__hash__())
False