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In 2.6a, seems like the __hash__ implementation and __eq__ must be
defined together, in the same class. See also #1549. Ensuring that a
__hash__ implementation isn't being pulled from a builtin type is
probably a sufficient check...?
>>> class Base(object):
... def __init__(self, name):
... self.name = name
... def __eq__(self, other):
... return self.name == other.name
... def __hash__(self):
... return hash(self.name)
... 
>>> class Extended(Base):
... def __eq__(self, other):
... print "trace: __eq__ called"
... return Base.__eq__(self, other)
... 
>>> hash(Base('b1'))
603887253
>>> hash(Extended('e1'))
Traceback (most recent call last):
 File "<stdin>", line 1, in <module>
TypeError: unhashable type: 'Extended'