#5308: Removing __len__ for combinatorial classes
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Reporter: hivert | Owner: hivert
Type: enhancement | Status: assigned
Priority: major | Milestone: sage-combinat
Component: combinatorics | Keywords: __len__, count, combinatorial class
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Description changed by hivert:
Old description:
> After some discussion on sage-combinat-devel, it was decided that __len__
> should no be used to get the size of a combinatorial class because.
> Indeed the specifications of __len__ says that it has to return a plain
> python int, whereas we want to deal with huge and even infinite sets.
> Unfortunately due to __len__ being called by list / filter / map and
> maybe some other functions, it is not possible to issue a warning. So it
> was decided to simply remove it and issue an error, telling to call
> .count() instead.
>
> Some part of combinat has to be fixed accordingly.
New description:
After some discussion on sage-combinat-devel, it was decided that
{{{__len__}}} should no be used to get the size of a combinatorial class.
Indeed the specifications of {{{__len__}}} says that it has to return a
plain python int, whereas we want to deal with huge and even infinite
sets. Unfortunately due to {{{__len__}}} being called by {{{list / filter
/ map}}} and maybe some other functions, it is not possible to issue a
warning. So it was decided to simply remove it and issue an error, telling
to call {{{.cardinality()}}} instead. The former usage of {{{.count()}}}
is also deprecated.
Combinat has to be adapted to this and also to the deprecation of
{{{iterator}}} in favor of {{{__iter__}}}
I'm preparing a patch to solve those issues.
Cheers,
Florent
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Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/5308#comment:2>
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