>>> class C(object):
...     def __init__(self, val):
...             self.val = val
...     def __cmp__(self, other):
...             return cmp(self.val, other.val)
...
>>> a = C("SPAM")
>>> b = C("EGGS")
>>> d = C("SPAM")
>>> c = a
>>> a is b
False
>>> a == b
False
>>> a == d
True
>>> a is d
False
>>> a is c
True
>>> a == c
True