Hi Nathann,
This is one very special case where the Parent/Element relation is
broken. First of all FiniteEnumeratedSet is not the parent of its
elements (it is a facade):
sage: F = FiniteEnumeratedSet([1, Partition([2,1]), Permutation([3,2,1])])
sage: F
{1, [2, 1], [3, 2, 1]}
sage: F[0].parent()
Integer Ring
sage: F[1].parent()
Partitions
sage: F[2].parent()
Standard permutations
FiniteEnumeratedSet is aimed to not modify the input it gets. So if
you feed it with Python objects which are not elements it will not
complain and you have to go with that. With Stepan we implemented a
TotallyOrderedFiniteSet which has an option for having the behaviour
you expected
sage: T = TotallyOrderedFiniteSet([1, Partition([2,1]),
Permutation([3,2,1])], facade=False)
sage: T[0]
1
sage: T[0].parent()
{1, [2, 1], [3, 2, 1]}
Cheers,
Vincent
2014-04-30 9:02 UTC+02:00, Nathann Cohen <nathann.co...@gmail.com>:
> Here is the problem I met today:
>
> sage: F = FiniteEnumeratedSet(("a","b","c")); F
> {'a', 'b', 'c'}
> sage: isinstance(F,Parent)
> True
> sage: F[0]
> 'a'
> sage: F[0].parent()
> ---------------------------------------------------------------------------
> AttributeError Traceback (most recent call last)
> <ipython-input-15-142f29211c68> in <module>()
> ----> 1 F[Integer(0)].parent()
>
> AttributeError: 'str' object has no attribute 'parent'
>
> Soooooooo sometimes you write code that applies to parents, and sometimes
> the elements know what their parents are, sometimes they don't....
>
> 1) Is that normal ?
> 2) If not, what do we do against it ?
>
> Have fun !
>
> Nathann
>
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