#20998: Removing deprecated cmp and __cmp__ in some pyx files
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Reporter: | Owner:
chapoton |
Type: | Status: needs_work
enhancement |
Priority: major | Milestone: sage-7.3
Component: | Resolution:
python3 |
Keywords: | Merged in:
Authors: | Reviewers: Jeroen Demeyer
Frédéric Chapoton |
Report Upstream: N/A | Work issues:
Branch: | Commit:
public/20998 | 750f6989bdd90aefe29db49fef6a0043c4363865
Dependencies: | Stopgaps:
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Changes (by jdemeyer):
* status: needs_info => needs_work
* reviewer: => Jeroen Demeyer
Comment:
1. '''free_algebra_element_letterplace.pyx''', '''semigroups_cython.pyx'''
and '''map.pyx''':
`__richcmp__` bypasses the coercion model which is usually not what you
want for `Element` classes. The rule of thumb is that any
comparison/arithmetic of Sage `Element`s should use the coercion model
unless there is a reason not to. Maybe for `FormalCompositeMap`, there is
not much point in using the coercion model. But
`FreeAlgebraElement_letterplace` and `LeftZeroSemigroupElement` really are
elements where coercion looks useful.
The `_cmp_` and `_richcmp_` methods come from the coercion model, so you
are guaranteed equal parents, which likely implies that both arguments are
instances of `FreeAlgebraElement_letterplace`, `LeftZeroSemigroupElement`
or `FormalCompositeMap`. In that case, you can just drop the type
comparison.
2. The function '''richcmp_shortcut''':
This should be removed and replaced by the standard Python function
`PyObject_RichCompare`. For an example on how to use it, see
`src/sage/structure/coerce.pyx`.
--
Ticket URL: <https://trac.sagemath.org/ticket/20998#comment:24>
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