From e27dc7230845aa341d9a0bf323fa14912713cf33 Mon Sep 17 00:00:00 2001
From: Guido van Rossum <guido@python.org>
Date: Tue, 27 Mar 2007 22:37:34 +0000
Subject: [PATCH] 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 |  6 ++++++
 Misc/NEWS                |  3 +++
 Objects/typeobject.c     | 17 ++++++++++++++++-
 3 files changed, 25 insertions(+), 1 deletion(-)

diff --git a/Lib/test/test_compare.py b/Lib/test/test_compare.py
index 1d0da692097..c6608379a13 100644
--- a/Lib/test/test_compare.py
+++ b/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)
 
diff --git a/Misc/NEWS b/Misc/NEWS
index c2699ec53ae..4f647d2be5e 100644
--- a/Misc/NEWS
+++ b/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.
 
diff --git a/Objects/typeobject.c b/Objects/typeobject.c
index e626a17f76c..be6f279466f 100644
--- a/Objects/typeobject.c
+++ b/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: