Trac #25978: Python 3: sorting issue causing failure in koszul_comple…

…x.py

A sorting issue (`TypeError: '>' not supported between instances of
'NoneType' and 'int'`) in `multi_polynomial_ring_base.pyx` causes a
doctest failure in `koszul_complex.py` in Python 3.

URL: https://trac.sagemath.org/25978
Reported by: jhpalmieri
Ticket author(s): John Palmieri
Reviewer(s): Travis Scrimshaw

src/sage/rings/polynomial/multi_polynomial_ring_base.pyx

@@ -938,7 +938,10 @@ cdef class MPolynomialRing_base(sage.rings.ring.CommutativeRing):
 
         counts, total = self._precomp_counts(n, degree)
 
-        if terms > total:
+        # Note that 'terms' could be None while 'total' is a
+        # nonnegative integer, so the comparison 'terms > total' could
+        # fail in Python 3.
+        if terms and terms > total:
             terms = total
 
         if terms is None: