#8766: document the _iadd_ and _imul_ special integer.pyx methods, which mutate
self
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Reporter: was | Owner: AlexGhitza
Type: defect | Status: new
Priority: major | Milestone: sage-4.4.2
Component: basic arithmetic | Keywords:
Author: | Upstream: N/A
Reviewer: | Merged:
Work_issues: |
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Comment(by was):
> This is odd. From their names one would expect them to be used in
__imul__
> and __iadd__ somewhere in the hierarchy, just like _repr_ is used in
> __repr__, so that they will be used for:
>
> sage: a = 1
> sage: a*=5
>
> as documented here: http://docs.python.org/reference/datamodel.html.
> However, this is not the case. It may be a bug (or yet to be implemented
> feature).
That is not a bug -- it is done on purpose. The reason is because
integers are meant to be *immutable*, since they have a hash method. If
_imul_ were used by __imul__, then people would be mutating integers left
and right by accident, and vast amounts of code would consequently have
subtle bugs all over the place.
There might have been a time (maybe a few weeks in 2006) when __imul__ did
indeed call _imul_ in Sage, so the name might be a historical remnant.
Personally, I think the best thing would be:
(1) Rename _imul_ and _iadd_ to something like _unsafe_inplace_mul_,
_unsafe_inplace_add_
(2) Document them.
William
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/8766#comment:3>
Sage <http://www.sagemath.org>
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