#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 strenner):
Replying to [comment:2 nbruin]:
> How about `a<2`, `2<a` then? Do you want the same there? That would give
an infinite recursion.
I am hoping that there exists an implementation that avoids infinite
recursion.
> In python, the meaning of comparison is in the hands of the left hand
side.
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):
"`NotImplemented` signals to the runtime that it should ask someone else
to satisfy the operation. In the expression `a == b`, if `a.__eq__(b)`
returns `NotImplemented`, then Python tries `b.__eq__(a)`. If b knows
enough to return True or False, then the expression can succeed. If it
doesn't, then the runtime will fall back to the built-in behavior (which
is based on identity for == and !=)."
For instance, if Sage could override this built-in behavior and try
coercion instead, that would save us from infinite recursion.
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Ticket URL: <http://trac.sagemath.org/ticket/15731#comment:3>
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