#15731: Too early coercion causes weird behavior of comparison
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Reporter: strenner | Owner:
Type: defect | Status: new
Priority: major | Milestone: sage-6.1
Component: coercion | Resolution:
Keywords: | Merged in:
Authors: | Reviewers:
Report Upstream: N/A | Work issues:
Branch: | Commit:
Dependencies: | Stopgaps:
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Comment (by nbruin):
Replying to [comment:3 strenner]:
> This is not entirely true. From
http://stackoverflow.com/questions/878943/why-return-notimplemented-
instead-of-raising-notimplementederror (the same thing works for other
comparison operators):
I'm not sure it's entirely true; see
[http://docs.python.org/2/reference/datamodel.html#object.__lt__] (the
official documentation tends to be a little more authoritative than
stackoverflow, and in the case of python, usually very clear too). Indeed,
these methods can return to `NotImplemented`, but I think that leads
python to try different variants, and never "swapped" (rather, it will try
`__ge__` after `__lt__` has failed). The final showstopper is probably the
older `__cmp__` protocol that predates python's "rich" comparisons and is
actually what is used most throughout sage. I don't see a "notImplemented"
escape documented for that. Normal python semantics seem to never swap LHS
and RHS for comparison operators, contrasting what python specifies for
`+` with `__add__` and `__radd__`
> For instance, if Sage could override this built-in behavior and try
coercion instead, that would save us from infinite recursion.
--
Ticket URL: <http://trac.sagemath.org/ticket/15731#comment:4>
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