Working on issue #1762: Brought

  ./python.exe -m timeit -s 'from fractions import Fraction; f = Fraction(3, 2)' 'isinstance(3, Fraction); isinstance(f, Fraction)'
from 12.3 usec/loop to 3.44 usec/loop and
  ./python.exe -m timeit -s 'from fractions import Fraction' 'Fraction(3, 2)'
from 48.8 usec to 23.6 usec by avoiding genexps and sets in __instancecheck__
and inlining the common case from __subclasscheck__.

1 files changed, 10 insertions, 0 deletions

diff --git a/Lib/test/test_abc.py b/Lib/test/test_abc.py
index 272f61df12..ac5f7ee245 100644
--- a/Lib/test/test_abc.py
+++ b/Lib/test/test_abc.py
@@ -83,6 +83,16 @@ class TestABC(unittest.TestCase):
         self.assertEqual(issubclass(C, A), True)
         self.assertEqual(isinstance(c, A), True)
 
+    def test_isinstance_invalidation(self):
+        class A:
+            __metaclass__ = abc.ABCMeta
+        class B(object):
+            pass
+        b = B()
+        self.assertEqual(isinstance(b, A), False)
+        A.register(B)
+        self.assertEqual(isinstance(b, A), True)
+
     def test_registration_builtins(self):
         class A:
             __metaclass__ = abc.ABCMeta