#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
----------------------------------------------------+-----------------------
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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Comment (by nbruin):
Are you sure
{{{
ZZ.convert_map_from(10)
}}}
should not raise an error? Shouldn't the argument be a parent? Something
like:
{{{
if not(isinstance(S,type) or
isinstance(type(S),sage.structure.parent.Parent):
raise TypeError('convert maps only exist from parents')
}}}
This has the potential for getting hairy if you want this to work:
{{{
sage: A=AdditiveGroups()
sage: A(ZZ)
Free commutative group on generators [1]
}}}
because then `parent(ZZ)` should be a Parent and it's not. However, this
doesn't seem to be the way categories work anyway and it's probably wise
to keep a strict separation between sets (parents) and categories. It
actually makes me wonder if parent(ZZ) should even work.
I know this all flies in the face of duck typing, but so does the whole
category framework. I'm afraid that a fully duck typed computer algebra
system would about as bad as an untyped one.
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/13378#comment:2>
Sage <http://www.sagemath.org>
Sage: Creating a Viable Open Source Alternative to Magma, Maple, Mathematica,
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