#12978: conditionally_defined decorator for methods and other attributes
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Reporter: nthiery | Owner: jason
Type: enhancement | Status:
Priority: major | needs_review
Component: misc | Milestone: sage-
Keywords: categories, | wishlist
conditionally_defined | Resolution:
Authors: | Merged in:
Report Upstream: N/A | Reviewers:
Branch: | Work issues:
Dependencies: #15056 | Commit:
| Stopgaps:
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Changes (by SimonKing):
* status: new => needs_review
Comment:
I have attached a new patch version, and now I think the
conditionally_defined wrapper is feature-complete. The documentation
provides extensive tests.
Restriction:
- We *must* have new style classes, since for an old style class there
seems to be no way to access the class hierarchy.
What one can do with the wrapper:
- It works on usual methods and special Python methods (`__hash__`,
`__len__`, ...)
- It works well in combination with other wrappers such as cached_method
and lazy_attribute.
- It works within the category framework. To make it work, if `B` is a
class, `B.bar` must yield the wrapper and not the unbound method in
default implementation.
- Even though `B.bar` is a wrapper, it behaves like an unbound method:
When calling it like `B.bar(b, *args, **kwds)` with `b` an instance of `B`
then it calls the default implementation on `b` with the given additional
arguments. Note that this is not necessarily the same as
`b.bar(*args,**kwds)`, because the latter may be the non-default
implementation inherited from a super-class.
- Introspection works. Again, since `B.bar` is a wrapper and not an
unbound method, we need some magic, namely methods `_sage_doc_`,
`_sage_src_` etc.
The only thing I can currently think of that does not work:
{{{
class A(object):
x = 5
class B(A):
@conditionally_defined(lambda x: x.condition>0)
x = 7
}}}
No idea how this can be made work.
I just realise that I forgot to add examples for the introspection method.
Once they are added, it can be reviewed!
--
Ticket URL: <http://trac.sagemath.org/ticket/12978#comment:25>
Sage <http://www.sagemath.org>
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