Anti-registration of various ABC methods.

- Issue #25958: Support "anti-registration" of special methods from
  various ABCs, like __hash__, __iter__ or __len__.  All these (and
  several more) can be set to None in an implementation class and the
  behavior will be as if the method is not defined at all.
  (Previously, this mechanism existed only for __hash__, to make
  mutable classes unhashable.)  Code contributed by Andrew Barnert and
  Ivan Levkivskyi.

1 files changed, 8 insertions, 0 deletions

diff --git a/Lib/test/test_augassign.py b/Lib/test/test_augassign.py
index 5093e9d0f3..5930d9e7a2 100644
--- a/Lib/test/test_augassign.py
+++ b/Lib/test/test_augassign.py
@@ -83,6 +83,10 @@ class AugAssignTest(unittest.TestCase):
             def __iadd__(self, val):
                 return aug_test3(self.val + val)
 
+        class aug_test4(aug_test3):
+            """Blocks inheritance, and fallback to __add__"""
+            __iadd__ = None
+
         x = aug_test(1)
         y = x
         x += 10
@@ -106,6 +110,10 @@ class AugAssignTest(unittest.TestCase):
         self.assertTrue(y is not x)
         self.assertEqual(x.val, 13)
 
+        x = aug_test4(4)
+        with self.assertRaises(TypeError):
+            x += 10
+
 
     def testCustomMethods2(test_self):
         output = []