Trac #26878: KleshchevPartitions: ensure that _element_constructor_ i…

…s a bound method

The `_element_constructor` machinery in `Parent` has support both for
`P._element_constructor_` being a bound and an unbound method. However,
there is exactly one case where an unbound method occurs and that is for
`KleshchevPartitions`.

It would be good to simplify the `_element_constructor` handling to
always assume a bound method, but then `KleshchevPartitions` must be
fixed.

URL: https://trac.sagemath.org/26878
Reported by: jdemeyer
Ticket author(s): Jeroen Demeyer
Reviewer(s): Travis Scrimshaw

src/sage/combinat/partition_kleshchev.py

@@ -85,7 +85,7 @@
 from sage.categories.infinite_enumerated_sets import InfiniteEnumeratedSets
 from sage.misc.lazy_attribute import lazy_attribute
 from sage.rings.all import NN, ZZ, IntegerModRing
-from sage.cpython.getattr import raw_getattr
+from sage.cpython.getattr import getattr_from_other_class
 
 from collections import defaultdict
 
@@ -1441,7 +1441,7 @@ def __init__(self, e, multicharge, convention):
         self._level = len(multicharge)
         if self._level == 1:
             self.Element = KleshchevPartitionCrystal
-            self._element_constructor_ = raw_getattr(Partitions, '_element_constructor_')
+            self._element_constructor_ = getattr_from_other_class(self, Partitions, '_element_constructor_')
         else:
             self.Element = KleshchevPartitionTupleCrystal
 
@@ -1638,7 +1638,7 @@ def __init__(self, e, multicharge=(0,), size=0, convention='RS'):
         self._level = len(multicharge)
         if self._level == 1:
             self.Element = KleshchevPartition
-            self._element_constructor_ = raw_getattr(Partitions, '_element_constructor_')
+            self._element_constructor_ = getattr_from_other_class(self, Partitions, '_element_constructor_')
         else:
             self.Element = KleshchevPartitionTuple
         super(KleshchevPartitions_size, self).__init__(category=FiniteEnumeratedSets())