#16269: Cartesian Products of additive groups
-------------------------------------+-------------------------------------
Reporter: ncohen | Owner:
Type: enhancement | Status: needs_review
Priority: major | Milestone: sage-6.2
Component: categories | Resolution:
Keywords: | Merged in:
Authors: Nathann Cohen, | Reviewers:
Nicolas M. Thiéry | Work issues:
Report Upstream: N/A | Commit:
Branch: u/ncohen/16269 | d22e245049e26dd10522d3514603868701a286fb
Dependencies: | Stopgaps:
-------------------------------------+-------------------------------------
Comment (by ncohen):
Yo !
> - CartesianProduct.__iter__ should be in
EnumeratedSets.CartesianProducts.ParentMethods
Done
> - In ``_add_``, ``self.parent(right)`` looks suspicious. Does it even
work?
> If the purpose is to convert ``right`` into the same parent as
> ``self``, then no need to worry about this: ``_add_`` may assume
> that its two arguments belong to the same parent.
That was the reason. Done.
> - I am uncomfortable with using ``__iter__`` and ``__getitem__`` for
> accessing the components of an element. For certain cartesian
> products (e.g. cartesian products of modules), ``__iter__`` may have
> a different meaning. Please use ``summand_split`` and
> ``summand_projection`` instead.
Here I do not agree. This is the most natural definition of an "iter" for
a cartesian product. Your application will overrule this anyway, so how
can that be a problem ?
> - In ``_element_constructor_``: given the catch, if we feed completely
> unrelated crap to the constructor, is there an exception raised as
> one could desire?
> {{{
> sage: GF(3)("a")
> Traceback (most recent call last)
> ...
> TypeError: unable to convert x (=a) to an integer
>
> sage: C = cartesian_product([GF(3), GF(3)])
> sage: C(["a","b"])
> ???
> }}}
Okay, so here I am stuck and I can't sort this out. Here is the problem :
{{{
sage: FiniteEnumeratedSet(["a","b","c"])("a")
TypeError: Cannot convert str to sage.structure.element.Element
sage: FiniteEnumeratedSet(["a","b","c"])("d")
ValueError: d not in {'a', 'b', 'c'}
}}}
Because you cannot trust `FiniteEnumeratedSet` to have a sound `__call__`
method, I need this try/catch.
On the other hand, if I have this try/catch, then I cannot detect
`GF(3)("e")` anymore. So what do we do ?
I personally see no problem in removing this catch, knowing that cartesian
products of `FiniteEnumeratedSet` will fail. For me it is because of a bug
in `FiniteEnumeratedSet`, not of what I implement.
Nathann
--
Ticket URL: <http://trac.sagemath.org/ticket/16269#comment:18>
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/d/optout.
