fix in other similar places

Author: vneiger

src/sage/rings/polynomial/polynomial_element.pyx

@@ -7667,9 +7667,12 @@ cdef class Polynomial(CommutativePolynomial):
 
         cdef unsigned long d
         if degree is not None:
-            d = degree
-            if d != degree:
-                raise ValueError("degree argument must be a non-negative integer, got %s"%(degree))
+            if degree <= 0:
+                raise ValueError("degree argument must be a non-negative integer, got %s" % (degree))
+            try:
+                d = degree
+            except ValueError:
+                raise ValueError("degree argument must be a non-negative inte ger, got %s" % (degree))
             if len(v) < degree+1:
                 v.reverse()
                 v = [self.base_ring().zero()]*(degree+1-len(v)) + v

src/sage/rings/polynomial/polynomial_integer_dense_flint.pyx

@@ -1827,9 +1827,12 @@ cdef class Polynomial_integer_dense_flint(Polynomial):
         cdef Polynomial_integer_dense_flint res = self._new()
         cdef unsigned long d
         if degree is not None:
-            d = degree
-            if d != degree:
-                raise ValueError("degree argument must be a non-negative integer, got %s" % degree)
+            if degree <= 0:
+                raise ValueError("degree argument must be a non-negative integer, got %s" % (degree))
+            try:
+                d = degree
+            except ValueError:
+                raise ValueError("degree argument must be a non-negative inte ger, got %s" % (degree))
             # FLINT expects length
             fmpz_poly_reverse(res._poly, self._poly, d+1)
         else:

src/sage/rings/polynomial/polynomial_zmod_flint.pyx

@@ -815,9 +815,12 @@ cdef class Polynomial_zmod_flint(Polynomial_template):
         cdef Polynomial_zmod_flint res = self._new()
         cdef unsigned long d
         if degree is not None:
-            d = degree
-            if d != degree:
-                raise ValueError("degree argument must be a non-negative integer, got %s"%(degree))
+            if degree <= 0:
+                raise ValueError("degree argument must be a non-negative integer, got %s" % (degree))
+            try:
+                d = degree
+            except ValueError:
+                raise ValueError("degree argument must be a non-negative inte ger, got %s" % (degree))
             nmod_poly_reverse(&res.x, &self.x, d+1) # FLINT expects length
         else:
             nmod_poly_reverse(&res.x, &self.x, nmod_poly_length(&self.x))

src/sage/rings/polynomial/polynomial_zz_pex.pyx

@@ -538,9 +538,12 @@ cdef class Polynomial_ZZ_pEX(Polynomial_template):
         # When a degree has been supplied, ensure it is a valid input
         cdef unsigned long d
         if degree is not None:
-            d = degree
-            if d != degree:
-                raise ValueError("degree argument must be a non-negative integer, got %s"%(degree))
+            if degree <= 0:
+                raise ValueError("degree argument must be a non-negative integer, got %s" % (degree))
+            try:
+                d = degree
+            except ValueError:
+                raise ValueError("degree argument must be a non-negative inte ger, got %s" % (degree))
             ZZ_pEX_reverse_hi(r.x, (<Polynomial_ZZ_pEX> self).x, d)
         else:
             ZZ_pEX_reverse(r.x, (<Polynomial_ZZ_pEX> self).x)