#16250: Monoids._test_one() incorrect for unhashable one elements
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Reporter: saraedum | Owner:
Type: defect | Status: needs_review
Priority: trivial | Milestone: sage-6.3
Component: categories | Resolution:
Keywords: hash | Merged in:
Authors: Julian Rüth | Reviewers:
Report Upstream: N/A | Work issues:
Branch: | Commit:
u/saraedum/ticket/16250 | 7b35c8a32ea67041665dddd8f1d98c7b8cfb6141
Dependencies: | Stopgaps:
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Comment (by saraedum):
Replying to [comment:6 nthiery]:
> I agree that it makes sense to disable the test if the object is not
> hashable. On the other hand, I would much prefer to have an explicit
> test like:
> {{{
> isinstance(..., collections.Hashable)
> }}}
I thought about this too. I agree that this would be better in theory. The
problem with this approach are things like matrices. They define a hash
which raises a `TypeError` if the matrix is mutable.
> Agreed, the right fix (tm) would probably be to remove the infamous
> `SageObject.__hash__` method in the first place. Not all SageObjects
> are hashable, and anyway computing the hash in term of `_repr_` is
> just a continuous source of bugs. But this fix could take some work
> since one would need to implement `__hash__` properly in a bunch of
> places; so let's say that this is for a separate ticket.
I agree. At first it seems that basing this on `_repr_` is exactly what
one wants. But the little work you save is just not worth all the trouble
it causes.
--
Ticket URL: <http://trac.sagemath.org/ticket/16250#comment:7>
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