#13814: LazyFamily.__eq__ gives false positives.
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Reporter: cnassau | Owner: sage-combinat
Type: defect | Status: needs_review
Priority: major | Milestone: sage-5.6
Component: combinatorics | Resolution:
Keywords: | Work issues:
Report Upstream: N/A | Reviewers:
Authors: Christian Nassau | Merged in:
Dependencies: | Stopgaps:
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Comment (by nthiery):
Hi Christian,
Replying to [comment:8 cnassau]:
> > ``__eq__`` and ``__ne__`` are supposed to be implemented consistently;
so
> > _test_pickling is allowed to rely on this assumption. If the
> > assumption fails, that's an equality bug which should be fixed in
> > ``__eq__/__ne__`` and be tested in ``_test_equal`` (whenever
possible).
>
> Well, I think it __is__ consistent to have
>
> {{{
> sage: LazyFamily(Integers(),lambda i:i) ==
LazyFamily(Integers(),lambda i:1*i)
> False
> sage: LazyFamily(Integers(),lambda i:i) !=
LazyFamily(Integers(),lambda i:1*i)
> False
> }}}
>
> In my reading this conforms to the standard python requirements:
>
> hashing only requires `__hash__` and `__eq__` in
> `http://docs.python.org/2/reference/datamodel.html#object.__hash__`
>
> The document also says
>
> There are no implied relationships among the comparison operators.
The truth of x==y does not imply that x!=y is false.
That's right for Python. However Sage is more stringent about this and
requires == and != to be consistent. Hmm, I am not sure this is
documented anywhere though. Basically the idea is that we already have
trouble maintaining a consistent specification and implementation for
==, so we can't really afford to also maintain a possibly different
specification for != ...
Cheers,
Nicolas
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/13814#comment:14>
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