bpo-33083 - Make math.factorial reject arguments that are not int-like (GH-6149)

math.factorial() was accepting non-integral Decimal instances. This is inconsistent with the actual behaviour for floats, which are not accepted.

Lib/test/test_math.py

@@ -5,6 +5,7 @@ from test.support import run_unittest, verbose, requires_IEEE_754
 from test import support
 import unittest
 import itertools
+import decimal
 import math
 import os
 import platform
@@ -510,6 +511,10 @@ class MathTests(unittest.TestCase):
         self.assertRaises(ValueError, math.factorial, -1e100)
         self.assertRaises(ValueError, math.factorial, math.pi)
 
+    def testFactorialNonIntegers(self):
+        self.assertRaises(TypeError, math.factorial, decimal.Decimal(5.2))
+        self.assertRaises(TypeError, math.factorial, "5")
+
     # Other implementations may place different upper bounds.
     @support.cpython_only
     def testFactorialHugeInputs(self):

Misc/NEWS.d/next/Core and Builtins/2018-03-19-00-59-20.bpo-33083.Htztjl.rst

+``math.factorial`` no longer accepts arguments that are not int-like.
+Patch by Pablo Galindo.

Modules/mathmodule.c

@@ -1656,7 +1656,7 @@ math_factorial(PyObject *module, PyObject *arg)
 {
     long x;
     int overflow;
-    PyObject *result, *odd_part, *two_valuation;
+    PyObject *result, *odd_part, *two_valuation, *pyint_form;
 
     if (PyFloat_Check(arg)) {
         PyObject *lx;
@@ -1672,8 +1672,14 @@ math_factorial(PyObject *module, PyObject *arg)
         x = PyLong_AsLongAndOverflow(lx, &overflow);
         Py_DECREF(lx);
     }
-    else
-        x = PyLong_AsLongAndOverflow(arg, &overflow);
+    else {
+        pyint_form = PyNumber_Index(arg);
+        if (pyint_form == NULL) {
+            return NULL;
+        }
+        x = PyLong_AsLongAndOverflow(pyint_form, &overflow);
+        Py_DECREF(pyint_form);
+    }
 
     if (x == -1 && PyErr_Occurred()) {
         return NULL;