#14167: UniqueRepresentation using default arguments
----------------------------------------------------------+-----------------
Reporter: SimonKing | Owner:
jason
Type: enhancement | Status:
needs_review
Priority: major | Milestone:
sage-5.8
Component: misc | Resolution:
Keywords: UniqueRepresentation default arguments | Work issues:
Report Upstream: N/A | Reviewers:
Authors: Simon King | Merged in:
Dependencies: #14054 | Stopgaps:
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Changes (by SimonKing):
* status: new => needs_review
Comment:
This ticket builds upon #14054, namely it uses the distinction of
`UniqueRepresentation` and `CachedRepresentation`.
The idea to make default arguments work is as follows. Let C be a subclass
of `CachedRepresentation`, and assume that it overrides `__init__`.
- I changed `weak_chached_function`, so that a function can be passed as
an optional parameter from which the argspec is taken.
- `CachedRepresentation.__classcall__` used to be a cached function,
stored as an attribute of `CachedRepresentation`. This will still be the
case. Of course, `CachedRepresentation` does not know about `C.__init__`.
Hence, `CachedRepresentation.__classcall__` has no default arguments.
- However, when the first instance of C is created, then
`CachedRepresentation.__classcall__` is called with C. In that moment,
`C.__init__` is available. `CachedRepresentation.__classcall__` will then
create a new weak_cached_function that uses the argspec of `C.__init__`.
This new weak_cached_function will override the cdef attribute
`C.classcall`, provided that `C.classcall` is the same as
`CachedRepresentation.__classcall__` (hence, a custom `__classcall__` or
`__classcall_private__` will be respected). The new weak_cached_function
creates, caches and returns the first instance of C.
- When the second instance of C is created, the new weak_cached_function
is called, and `CachedRepresentation.__classcall__` is not involved any
more.
- Since only `C.classcall` is overridden, but not `C.__classcall__`, it is
no problem to subclass C: If D is a subclass of C, then the first instance
of D will be created in `CachedRepresentation.__classcall__`, which will
override D.classcall, but does not affect C.classcall.
__Smaller changes__
- `ClasscallMetaclass` gets methods `_get_caller_` and
`_overload_caller_`, so that one can retrieve or overload C.classcall from
a Python module.
- `WeakCachedFunction.__init__` gets a new optional argument
`argspec_from`, which is supposed to be a function from which the cached
function gets its defaults. `argspec_from` is passed down to the weak
cached function's "_argument_fixer`, whose job it is to take care of
default arguments.
- In `sage.misc.superseded._check_trac_number`, I remove the import of
`is_Integer`. Namely, at least with some preliminary version of the patch,
this import used to crash Sage during startup. What we want to know in
this function is whether the given trac number is a positive integer. I
suggest to do a very similar thing to the default containment test of
parents: trac_number is an integer if `int(trac_number)==trac_number`
returns True and does not raise an error.
- I use `.. TODO::` and similar directives in a couple of cases.
Needs review, then!
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/14167#comment:1>
Sage <http://www.sagemath.org>
Sage: Creating a Viable Open Source Alternative to Magma, Maple, Mathematica,
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