By default, != returns the opposite of ==, unless the latter returns

NotImplemented.

(Is this worth backporting to 2.6?  It seems so useful...!)

Lib/test/test_compare.py

@@ -39,6 +39,12 @@ class ComparisonTest(unittest.TestCase):
                 self.assertEqual(a == b, id(a) == id(b),
                                  'a=%r, b=%r' % (a, b))
 
+    def test_ne_defaults_to_not_eq(self):
+        a = Cmp(1)
+        b = Cmp(1)
+        self.assertTrue(a == b)
+        self.assertFalse(a != b)
+
 def test_main():
     test_support.run_unittest(ComparisonTest)
 

Misc/NEWS

@@ -28,6 +28,9 @@ TO DO
 Core and Builtins
 -----------------
 
+- By default, != returns the opposite of ==, unless the latter returns
+  NotImplemented.
+
 - Patch #1680961: sys.exitfunc has been removed and replaced with a private
   C-level API.
 

Objects/typeobject.c

@@ -2314,7 +2314,22 @@ object_richcompare(PyObject *self, PyObject *other, int op)
 		break;
 
 	case Py_NE:
-		res = (self != other) ? Py_True : Py_False;
+		/* By default, != returns the opposite of ==,
+		   unless the latter returns NotImplemented. */
+		res = PyObject_RichCompare(self, other, Py_EQ);
+		if (res != NULL && res != Py_NotImplemented) {
+			int ok = PyObject_IsTrue(res);
+			Py_DECREF(res);
+			if (ok < 0)
+				res = NULL;
+			else {
+				if (ok)
+					res = Py_False;
+				else
+					res = Py_True;
+				Py_INCREF(res);
+			}
+		}
 		break;
 
 	default: