Added normalization to enumerated_sets to prevent an infinite index. Added doctest for infinite index. Also added to

unrank direct test to get full code coverage.

Author: Noel Roemmele

src/sage/categories/enumerated_sets.py

@@ -457,10 +457,23 @@ def __getitem__(self, i):
                 [1]
                 sage: F[1::2]
                 [2]
+
+            TESTS:
+
+            Verify that an infinite index raises an error::
+
+                sage: F = FiniteEnumeratedSet([1,2,3,4,5])
+                sage: F[oo]
+                Traceback (most recent call last):
+                ...
+                TypeError: unable to coerce <class 'sage.rings.infinity.PlusInfinity'>
+                to an integer
             """
             from sage.rings.infinity import Infinity
+            from sage.rings.integer_ring import ZZ
             if isinstance(i, slice):
                 return self.unrank_range(i.start, i.stop, i.step)
+            i = ZZ(i)
             if i < 0:
                 i += self.cardinality()
             if i < 0:

src/sage/combinat/tuple.py

@@ -152,6 +152,10 @@ def unrank(self, i):
             sage: T = Tuples(range(4), 3)
             sage: T.unrank(19)
             (3, 0, 1)
+            sage: T.unrank(-1)
+            Traceback (most recent call last):
+            ...
+            IndexError: index out of range
 
         Verify that :issue:`39534` has been fixed::