Merge branch 'u/saraedum/ticket/16251' of git://trac.sagemath.org/sage into ticket/16316

Author: saraedum

src/sage/rings/polynomial/multi_polynomial.pxd

@@ -1,4 +1,4 @@
 from sage.structure.element cimport CommutativeRingElement
 
 cdef class MPolynomial(CommutativeRingElement):
-    cdef long _hash_c(self)
+    cdef long _hash_c(self) except -1

src/sage/rings/polynomial/multi_polynomial.pyx

@@ -551,7 +551,7 @@ cdef class MPolynomial(CommutativeRingElement):
                 D[ETuple(tmp)] = a
             return D
 
-    cdef long _hash_c(self):
+    cdef long _hash_c(self) except -1:
         """
         This hash incorporates the variable name in an effort to respect the obvious inclusions
         into multi-variable polynomial rings.
@@ -577,6 +577,19 @@ cdef class MPolynomial(CommutativeRingElement):
             sage: f=x/y
             sage: f.subs({x:1})
             1/y
+
+        TESTS:
+
+        Verify that :trac:`16251` has been resolved, i.e., polynomials with
+        unhashable coefficients are unhashable::
+
+            sage: K.<a> = Qq(9)
+            sage: R.<t,s> = K[]
+            sage: hash(t)
+            Traceback (most recent call last):
+            ...
+            TypeError: unhashable type: 'sage.rings.padics.padic_ZZ_pX_CR_element.pAdicZZpXCRElement'
+
         """
         cdef long result = 0 # store it in a c-int and just let the overflowing additions wrap
         cdef long result_mon

src/sage/rings/polynomial/polynomial_element.pxd

@@ -14,7 +14,7 @@ cdef class Polynomial(CommutativeAlgebraElement):
     cdef char _is_gen
     cdef CompiledPolynomialFunction _compiled
     cpdef Polynomial truncate(self, long n)
-    cdef long _hash_c(self)
+    cdef long _hash_c(self) except -1
     cpdef constant_coefficient(self)
     cpdef Polynomial _new_constant_poly(self, a, Parent P)
 

src/sage/rings/polynomial/polynomial_element.pyx

@@ -835,7 +835,7 @@ cdef class Polynomial(CommutativeAlgebraElement):
     def __hash__(self):
         return self._hash_c()
 
-    cdef long _hash_c(self):
+    cdef long _hash_c(self) except -1:
         """
         This hash incorporates the variable name in an effort to respect
         the obvious inclusions into multi-variable polynomial rings.
@@ -858,6 +858,19 @@ cdef class Polynomial(CommutativeAlgebraElement):
             sage: R.<x>=IntegerModRing(11)[]
             sage: hash(R.0)==hash(FractionField(R).0)  # respect inclusions into the fraction field
             True
+
+        TESTS:
+
+        Verify that :trac:`16251` has been resolved, i.e., polynomials with
+        unhashable coefficients are unhashable::
+
+            sage: K.<a> = Qq(9)
+            sage: R.<t> = K[]
+            sage: hash(t)
+            Traceback (most recent call last):
+            ...
+            TypeError: unhashable type: 'sage.rings.padics.padic_ZZ_pX_CR_element.pAdicZZpXCRElement'
+
         """
         cdef long result = 0 # store it in a c-int and just let the overflowing additions wrap
         cdef long result_mon
@@ -866,9 +879,9 @@ cdef class Polynomial(CommutativeAlgebraElement):
         cdef int i
         for i from 0<= i <= self.degree():
             if i == 1:
-                # we delay the hashing until now to not waste it one a constant poly
+                # we delay the hashing until now to not waste it on a constant poly
                 var_name_hash = hash((<ParentWithGens>self._parent)._names[0])
-            #  I'm assuming (incorrectly) that hashes of zero indicate that the element is 0.
+            # I'm assuming (incorrectly) that hashes of zero indicate that the element is 0.
             # This assumption is not true, but I think it is true enough for the purposes and it
             # it allows us to write fast code that omits terms with 0 coefficients.  This is
             # important if we want to maintain the '==' relationship with sparse polys.