On Sat, 2 Sept 2023 at 08:44, 'Martin R' via sage-devel
<sage-devel@googlegroups.com> wrote:
>
> If I understand correctly, in python3 it is no longer necessary to implement
> __ne__, if it is simply the negation of __eq__.
>
> There are currently about 200 definitions of the form
>
> def __ne__(self, other):
> return not (self == other)
>
> I think it would be good to remove them.
SymPy removed most of its __ne__ methods but a few had to be kept. The
exception is that if any superclass defines __ne__ then a subclass
that overrides __eq__ must also override __ne__ to keep them
consistent. Obviously if you control both classes then you can remove
__ne__ from both but in SymPy's case some classes subclass builtin
types that cannot be changed:
class PolyElement(dict):
def __eq__(self, other):
# override dict.__eq__
def __ne__(self, other):
# also need to override dict.__ne__
I don't know if that applies to any of the 200 __ne__ methods in Sage
but I would check the mro in each case before removing __ne__. It is
easy for this sort of thing to be overlooked in test code and in fact
messing with __eq__/__ne__ (more so __eq__) can invalidate much of the
test suite so I would tread carefully.
--
Oscar
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