I managed to reproduce this on both Python 3.4 and 3.7.
Consider:
class Comparable:
def _key(self):
raise NotImplementedError
def __hash__(self):
return hash(self._key())
def __eq__(self, other):
...
def __lt__(self, other):
...
class A(Comparable): pass
class B(A):
def __str__(self):
return "d"
def __eq__(self, other):
return isinstance(self, type(other))
def _key(self):
return str(self),
b = B()
Clearly one would expect b.__hash__
to be defined here, since it is defined under Comparable
which B
is a subclass of.
Lo and behold, it is defined, but evaluates to None
. What gives?
>> b
<__main__.B object at 0x00000183C9734978>
>> '__hash__' in dir(b)
True
>> b.__hash__
>> b.__hash__ is None
True
>> B.__mro__
(<class '__main__.B'>, <class '__main__.A'>, <class '__main__.Comparable'>, <class 'object'>)
>> isinstance(b, Comparable)
True
The same behavior is reproduced if implementing __init__
as super().__init__()
in Comparable
and A
.
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