Hi Nils!
On Fri, Nov 09, 2012 at 08:44:15AM -0800, Nils Bruin wrote:
> On Nov 9, 2:11 am, "Nicolas M. Thiery" <nicolas.thi...@u-psud.fr>
> wrote:
> > The main point is that writing V.sum(args) gives more information to
> > the system than sum(args, self.zero()): this is making a promise that
> > all elements in args are elements of V.
>
> In python's call dispatch system, it does not. It says something along
> the lines: "Use V" to add up these arguments.
Yes, that's what I mean by ``giving more information'': V has the
required information to do it fast, so use it.
> I guess the convention could be that if someone calls this, then
> they should make sure that "args" only involves elements from V.
This is indeed the intended precondition, as stated in the
documentation of CommutativeAdditiveMonoids.ParentMethods.sum:
- ``args`` -- a list (or iterable) of elements of ``self``
Granted: ``element of`` is a bit vague. The exact intention is that
``self.is_parent_of(x)`` holds for all x in the sum.
> But then V.sum(W) would not be valid in interesting cases either
> (apart from probably not being a finite operation).
If such a feature is desired at some point, then I would want it to be
implemented in a different method.
Cheers,
Nicolas
--
Nicolas M. Thiéry "Isil" <nthi...@users.sf.net>
http://Nicolas.Thiery.name/
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