#14912: UniqueRepresentation tutorial could use more love
--------------------------------------------+------------------------------
Reporter: darij | Owner:
Type: defect | Status: needs_review
Priority: major | Milestone: sage-5.13
Component: documentation | Resolution:
Keywords: documentation, structure | Merged in:
Authors: Simon King | Reviewers: Darij Grinberg
Report Upstream: N/A | Work issues:
Branch: | Commit:
Dependencies: | Stopgaps:
--------------------------------------------+------------------------------
Comment (by SimonKing):
Replying to [comment:23 darij]:
> Sorry for letting this slip off my to-do list!
Same here...
> I'm pretty sure that I've understood the important points of the doc now
except for some that concern pickling (I don't know how it works and
frankly I didn't plan on learning that). I'd feel better if I knew what
exactly {{{__classcall__}}} does and (as I said) how it is distinguished
from {{{__new__}}} and {{{__init__}}} (and if it calls them, in which
order), but that might as well be a different patch.
In a nutshell: If `C` is a class with `ClasscallMetaclass`, then
`__classcall__` (or `__classcall_private__`) is what is executed when you
do `C(*args, **kwds)`.
Your `__classcall__` can do ''anything''. Really. It could return an
instance of `C`, but it could also return something totally different.
Consequence: `__new__` or `__init__` are ''only'' called if you did not
forget to call them inside of your `__classcall__`. If you look at what
`CachedRepresentation.__classcall__` does, you see that indeed `__new__`
and `__init__` are called explicitly.
> I'd like more details on this:
> {{{
> 104 In addition, it is required that a unique factory instance is
provided
> 105 with a name that allows to find its definition.
> }}}
> I assume this refers to the string parameter, e. g., in {{{F =
MyFactory("__main__.F")}}};
Exactly.
> but what kind of path should it contain if it is to be used somewhere in
a .py file rather than in a doctest? Just {{{F = MyFactory("F")}}} ?
It is exactly as it is stated: A name is needed that allows to find the
factory's definition. Hence, if you put `F` into the global name space,
then `F = MyFactory("F")` is fine. If `F` is in a module `sage.foo.bar`,
then it is `F = MyFactory("sage.foo.bar.F")`.
> What if it is defined inside a class?
If the class is `sage.bar.foo.MyClass` and you want to use a factory for
the attribute `F` of this class, then I guess it is `F =
MyFactory("sage.bar.foo.MyClass.F"). Not tested, though.
> Not sure about this:
> {{{
> And
> 408 with a factory, it is possible to create the resulting
instance by arguments
> 409 that are different from the key used for caching.
> }}}
> Doesn't that also work with CachedRepresentation if one preprocesses by
declaring {{{__classcall_private__}}}?
Yes. This could be clarified.
--
Ticket URL: <http://trac.sagemath.org/ticket/14912#comment:25>
Sage <http://www.sagemath.org>
Sage: Creating a Viable Open Source Alternative to Magma, Maple, Mathematica,
and MATLAB
--
You received this message because you are subscribed to the Google Groups
"sage-trac" group.
To unsubscribe from this group and stop receiving emails from it, send an email
to [email protected].
To post to this group, send email to [email protected].
Visit this group at http://groups.google.com/group/sage-trac.
For more options, visit https://groups.google.com/groups/opt_out.
