Actually that example helps. My understanding is that setting facade=True
allows the elements to have arbitrary objects, necessarily even elements.
For example:
sage: S = FiniteEnumeratedSet([1, Permutation([1,3,2]), Word('a')]); S
{1, [1, 3, 2], word: a}
sage: S[0].parent()
Integer Ring
sage: S[1].parent()
Traceback
...
AttributeError: 'Permutation_class' object has no attribute 'parent'
sage: S[2].parent()
Words
Perhaps it would be better it would be better to set _facade_for = facade
in parent.pyx by un-indenting the line one step in Parent.__init__() rather
than doing a getattr(). I'll also write a quick patch updating the
documentation for facade parents explaining the facade True.
Thanks,
Travis
On Wednesday, December 5, 2012 11:51:45 PM UTC-8, Vincent Delecroix wrote:
>
> An example in sage.sets.finite_enumerated_set. But an example is not
> an explanation ;-)
>
> 2012/12/6 Travis Scrimshaw <tsc...@ucdavis.edu <javascript:>>:
> > What is the reason why facade=True is allowable by Parent? It seems
> like
> > we always want to pass in the parent(s) which our facade parent is
> acting
> > for.
> >
> > On Wednesday, December 5, 2012 8:23:01 AM UTC-8, Vincent Delecroix
> wrote:
> >>
> >> I just upload on trac a patch about the initialisation of facade sets
> >> at #13801. One of the smallest patch I never write... which corrects
> >> two errors.
> >>
>
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