On Saturday, April 18, 2015 at 7:36:36 PM UTC-4, Darij Grinberg wrote:
>
> OK, so this is wrong?
>
> sage: u = StandardTableau( [[1,2],[3,4],[5]]
> ).standard_number_of_descents()
> sage: parent(u)
> <type 'int'>
>
> sage: u = Partition([3,2]).length()
> sage: parent(u)
> <type 'int'>
>
> sage: u = Partition([3,2]).frobenius_rank()
> sage: parent(u)
> <type 'int'>
>
> sage: u = SetPartition([[1], [2,3], [4]]).base_set_cardinality()
> sage: parent(u)
> <type 'int'>
>
Yes, imho those are all bugs. The only place where Sage should return int
is in Python magic methods, e.g. __len__
> I fear this kind of stuff exists throughout sage-combinat... and I have
> never encountered it causing problems.
>
x.cardinality().factor() should always work (unless it is inifinite).
A kind of corner case is if your code just works by duck-typing without
>> ever needing a literal number. Then you should probably rely on coercion to
>> do the right thing, so the output type matches the input type.
>>
>
> This I don't understand...
>
def add_two_numbers(x,y):
return x+y # no need to convert explicitly to ZZ
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