On Mon, Mar 3, 2008 at 8:23 PM, Michael Bayer <[EMAIL PROTECTED]> wrote:
> We define __eq__() all over the place so that would be a lot of
> __hash__() methods to add, all of which return id(self). I wonder if
> we shouldn't just make a util.Mixin called "Hashable" so that we can
> centralize the idea.
Are you sure this is a correct way? Below is an example demonstrating
the problem with it:
>>> class C(object):
... def __init__(self, value):
... self._value = value
... def __eq__(self, other):
... return self._value==other._value
... def __hash__(self):
... return id(self)
...
>>> c1 = C(1)
>>> c2 = C(1)
>>> c1==c2
True
>>> d = {c1: None}
>>> c1 in d
True
>>> c2 in d
False
I.e. although c2 is equal to c1 and thus should be found in
dictionary, it is not. The defined __hash__ method must return equal
numbers for equal object.
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