#10963: More functorial constructions
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Reporter: nthiery | Owner: stumpc5
Type: enhancement | Status: needs_work
Priority: major | Milestone: sage-6.1
Component: categories | Resolution:
Keywords: days54 | Merged in:
Authors: Nicolas M. Thiéry | Reviewers: Simon King, Frédéric
Report Upstream: N/A | Chapoton
Branch: | Work issues:
public/ticket/10963 | Commit:
Dependencies: #11224, #8327, | bdefe0daeb7a4154a506f5ac69a064b6150f8de6
#10193, #12895, #14516, #14722, | Stopgaps:
#13589, #14471, #15069, #15094, |
#11688, #13394, #15150, #15506 |
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Comment (by SimonKing):
Replying to [comment:273 nbruin]:
> That sounds like it's not going to work correctly if one is inheriting
from a class that has a value for the attribute already.
1. If I understand correctly, we are not supposed to subclass a category
with axiom.
2. If we ''do'' subclass a category with axiom, `hasattr(nested_cls,
"_base_category_class_and_axiom")` would indeed return True when
nested_cls is a subclass of something that has this attribute. However,
this is in fact not what we want. We would rather want that the subclass
has its own attribute. At least this is my guess what we ''would'' want,
if we were to create a subclass (which we don't).
> I don't think it's a good idea to move away from normal attribute lookup
semantics in python.
I think the normal attribute lookup semantics in python simply is the
wrong tool here. Actually we don't need `hasattr` at all, since we know
for sure that the class ''has'' the attribute (namely: lazy class
attribute). What we want to know is: Is this lazy attribute computed or
not? And hasattr can certainly not answer that question.
--
Ticket URL: <http://trac.sagemath.org/ticket/10963#comment:277>
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