#13378: Do not cache the non-existence of coerce/convert map too often, and do
not
pretend that there is a conversion where it doesn't make sense at all
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Reporter: SimonKing | Owner: robertwb
Type: defect | Status: new
Priority: major | Milestone: sage-5.3
Component: coercion | Resolution:
Keywords: coercion conversion object cache | Work issues:
Report Upstream: N/A | Reviewers:
Authors: | Merged in:
Dependencies: | Stopgaps:
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Description changed by SimonKing:
Old description:
> Sorry for the long ticket title.
>
> About the first part of the title:
> {{{
> sage: P.<x,y> = QQ[]
> sage: P.is_coercion_cached(x)
> False
> sage: P.coerce_map_from(x)
> sage: P.is_coercion_cached(x)
> True
> }}}
> Hence, there is a reference to x in the coercion cache for P. OK, by #715
> and friends, the reference is weak --- unless x does not allow weak
> references, in which case the reference will be strong, and x would not
> be collectable. Hence, a potential memory leak.
>
> About the second part:
> {{{
> sage: ZZ.convert_map_from(1)
> Conversion map:
> From: Set of Python objects of
> To: Integer Ring
> }}}
> or
> {{{
> sage: P.convert_map_from(x)
> Traceback (most recent call last):
> ...
> TypeError: Cannot convert
> sage.rings.polynomial.multi_polynomial_libsingular.MPolynomial_libsingular
> to sage.structure.parent.Parent
> }}}
> In both cases, I believe the answer should be "None".
New description:
Sorry for the long ticket title.
About the first part of the title:
{{{
sage: P.<x,y> = QQ[]
sage: P.is_coercion_cached(x)
False
sage: P.coerce_map_from(x)
sage: P.is_coercion_cached(x)
True
}}}
Hence, there is a reference to x in the coercion cache for P. OK, by #715
and friends, the reference is weak --- unless x does not allow weak
references, in which case the reference will be strong, and x would not be
collectable. Hence, a potential memory leak.
About the second part:
{{{
sage: ZZ.convert_map_from(1)
Conversion map:
From: Set of Python objects of
To: Integer Ring
}}}
or
{{{
sage: P.convert_map_from(x)
Traceback (most recent call last):
...
TypeError: Cannot convert
sage.rings.polynomial.multi_polynomial_libsingular.MPolynomial_libsingular
to sage.structure.parent.Parent
}}}
I think it is not good that the error occurs. The answer of
`ZZ.convert_map_from(1)` seems strange, but apparently those things
actually occur, namely conversions from the category of sequences.
--
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/13378#comment:1>
Sage <http://www.sagemath.org>
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