On Sunday, October 20, 2013 5:49:07 PM UTC-7, Anne Schilling wrote:
>
>
> > With regard to `Composition`, I do not have any strong feelings. I do
> not see anything wrong with having both `IntegerComposition` and
> `Partition` in the name-space. On the other hand, since no one
> > has noticed a problem with `Composition` before I don't really
> understand why there is suddenly a problem now, especially as there already
> is a much superior notation already available for the
>
> The problem became apparent from the ticket headline title "Composition
accepts too many inputs", while some rather obvious possible inputs that
are clearly composable are not accepted, so the opposite would seem the
case.
The problem does not arise if it is stated that
"sage.combinat.composition.Composition accepts too many inputs".
The issue is that when Composition gets imported into the global namespace,
the context is lost and you end up with a routine that has a rather
ambiguous name.
Global namespace is a scarce resource that we have to be careful with,
especially because changes to global namespace are incredibly painful.
I don't see a reason why sage.combinat.composition.Composition needs to be
exposed in the global namespace at all, since it's an element class, not a
parent. One can easily create compositions without referencing
"Composition" explicitly:
sage: Compositions()([2,3,5,6])
[2, 3, 5, 6]
which would be more efficient anyway, because that is what the metaclass
machinery on Composition does after some indirection. So it may actually be
that Composition on global level is ripe for deprecation anyway.
This is really a plea to be very careful with choosing what to expose in
the global namespace. It's the one place where different mathematics areas
do have to interface with each other. Note that there is a way out here,
which may not be immediately necessary: instead of just importing
Composition into the global namespace, put a routine there that dispatches
on input type:
def Composition(*args):
if len(args) == 1:
try:
_=Sequences(ZZ)(args[0])
return sage.combinat.composition.Composition(args[0])
except ...
<do other processing here>
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