Dear Amritanshu,
On Thu, Jun 13, 2013 at 10:19:32PM -0700, Amritanshu Prasad wrote:
> I am trying to define a class with parent EnumeratedSets whose constructor
> takes a list as an input.
> I tried:
> class MyExample(UniqueRepresentation, Parent):
> def __init__(self, input):
> self._input = input
> def __repr__(self):
> return str(self._input)
> but when I said
> MyExample([2,2])
> I got:
>
> Traceback (most recent call last):
> TypeError: unhashable type: 'list'
>
> I would be grateful if someone could explain why this happens, and how to
> get around it.
Good question! Which luckily has a good answer :-) See the section
"Argument preprocessing" in the documentation of CachedRepresentation:
http://sagemath.org/doc/reference/structure/sage/structure/unique_representation.html
or equivalently:
sage: UniqueRepresentation??
By the way: in your __init__ you probably want a line of the form:
Parent.__init__(self, category=EnumeratedSets())
and __repr__ should be _repr_. For an example, see:
sage: C = FiniteEnumeratedSets().example()
sage: C
An example of a finite enumerated set: {1,2,3}
sage: C??
Kind regards,
Nicolas
--
Nicolas M. Thiéry "Isil" <nthi...@users.sf.net>
http://Nicolas.Thiery.name/
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