Hi Travis!
Answering on sage-combinat-devel since trac access is to slooooow from here.
----- Forwarded message from Sage <wst...@math.washington.edu> -----
Right now the category `FiniteEnumeratedSets` overrides a parent class's
`cardinality()` when creating a list. Below is a minimal example of this
behavior:
{{{
from sage.structure.parent import Parent
from sage.categories.finite_enumerated_sets import FiniteEnumeratedSets
class TestParent(Parent):
def __init__(self):
Parent.__init__(self, category=FiniteEnumeratedSets())
def __iter__(self):
yield 1
return
def cardinality(self, n):
"""
EXAMPLES::
sage: P = sage.combinat.category_doctest_fail.TestParent()
sage: P.cardinality(-1)
-1
sage: v = P.list(); v
[1]
sage: len(v)
1
sage: P.cardinality()
1
sage: P.cardinality(-1) # This test breaks
-1
"""
return n
}}}
This seems to be caused by not checking if the parent class has a
`cardinality()` function implemented, and just overriding it with
`_cardinality_from_list()` (which takes no [optional] parameters).
------------------------------------------------------------------------------
Yes: under the current conventions, the cardinality method is not
supposed to take an argument. So if the list of elements has been
computed, it can be safely overwritten by something faster.
Do you have a strong rationale for deviating from the conventions?
Cheers,
Nicolas
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Nicolas
--
Nicolas M. Thiéry "Isil" <nthi...@users.sf.net>
http://Nicolas.Thiery.name/
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