bpo-35606: Fix math.prod tests using 'start' as keyword parameter (GH-28595) (GH-28604)

(cherry picked from commit 8497514)

Co-authored-by: Pablo Galindo Salgado <[email protected]>

Author: miss-islington

Lib/test/test_math.py

@@ -1724,16 +1724,22 @@ def test_prod(self):
         self.assertRaises(TypeError, prod)
         self.assertRaises(TypeError, prod, 42)
         self.assertRaises(TypeError, prod, ['a', 'b', 'c'])
-        self.assertRaises(TypeError, prod, ['a', 'b', 'c'], '')
-        self.assertRaises(TypeError, prod, [b'a', b'c'], b'')
+        self.assertRaises(TypeError, prod, ['a', 'b', 'c'], start='')
+        self.assertRaises(TypeError, prod, [b'a', b'c'], start=b'')
         values = [bytearray(b'a'), bytearray(b'b')]
-        self.assertRaises(TypeError, prod, values, bytearray(b''))
+        self.assertRaises(TypeError, prod, values, start=bytearray(b''))
         self.assertRaises(TypeError, prod, [[1], [2], [3]])
         self.assertRaises(TypeError, prod, [{2:3}])
-        self.assertRaises(TypeError, prod, [{2:3}]*2, {2:3})
-        self.assertRaises(TypeError, prod, [[1], [2], [3]], [])
+        self.assertRaises(TypeError, prod, [{2:3}]*2, start={2:3})
+        self.assertRaises(TypeError, prod, [[1], [2], [3]], start=[])
+
+        # Some odd cases
+        self.assertEqual(prod([2, 3], start='ab'), 'abababababab')
+        self.assertEqual(prod([2, 3], start=[1, 2]), [1, 2, 1, 2, 1, 2, 1, 2, 1, 2, 1, 2])
+        self.assertEqual(prod([], start={2: 3}), {2:3})
+
         with self.assertRaises(TypeError):
-            prod([10, 20], [30, 40])     # start is a keyword-only argument
+            prod([10, 20], 1)     # start is a keyword-only argument
 
         self.assertEqual(prod([0, 1, 2, 3]), 0)
         self.assertEqual(prod([1, 0, 2, 3]), 0)

Modules/mathmodule.c

@@ -2969,14 +2969,9 @@ math_prod_impl(PyObject *module, PyObject *iterable, PyObject *start)
     }
 
     if (result == NULL) {
-        result = PyLong_FromLong(1);
-        if (result == NULL) {
-            Py_DECREF(iter);
-            return NULL;
-        }
-    } else {
-        Py_INCREF(result);
+        result = _PyLong_One;
     }
+    Py_INCREF(result);
 #ifndef SLOW_PROD
     /* Fast paths for integers keeping temporary products in C.
      * Assumes all inputs are the same type.
@@ -2992,7 +2987,7 @@ math_prod_impl(PyObject *module, PyObject *iterable, PyObject *start)
         }
         /* Loop over all the items in the iterable until we finish, we overflow
          * or we found a non integer element */
-        while(result == NULL) {
+        while (result == NULL) {
             item = PyIter_Next(iter);
             if (item == NULL) {
                 Py_DECREF(iter);