#18383: Coercion and comparison for alternating sign matrices
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Reporter: vdelecroix | Owner:
Type: enhancement | Status: needs_work
Priority: major | Milestone: sage-6.7
Component: combinatorics | Resolution:
Keywords: | Merged in:
Authors: Vincent Delecroix | Reviewers:
Report Upstream: N/A | Work issues:
Branch: | Commit:
u/vdelecroix/18383 | 390e2d7cf57899cde4c7b096ef5b97f0be909574
Dependencies: | Stopgaps:
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Comment (by vdelecroix):
Replying to [comment:13 tscrim]:
> We have to care about Python3 because it is the way going forward. The
subtlety has come from us implementing a `__cmp__` at the general
`Element` level, which gets called by the `cmp` first, and then instead of
the default Python implementation of checking `__eq__` and `__lt__`, it
tries to call `_cmp_` and then `_richcmp_`. This is a subtly caused by the
current machinery in Sage. We need a mechanism which falls back to the
usual Python rich comparisons for compatibility (although perhaps we need
to make a single underscored version to work with coercion, but that is a
question for sage-devel and I think there's already discussions about
this).
This is not that simple because at the level of the C API `__eq__`,
`__lt__` etc does not exist. So there will be a huge difference between
extension classes (ie Cython) and Python classes (ie Python). The uniform
way that is proposed is precisely to use `_cmp_` or `_richcmp_` and avoid
`__eq__`, etc.
The fact that there is a global `__cmp__` in `Element` might be a problem
but this is rather disjoint from the present ticket: for ASM we want
coercion to be involved.
Vincent
--
Ticket URL: <http://trac.sagemath.org/ticket/18383#comment:14>
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