bpo-39382: Avoid dangling object use in abstract_issubclass() (GH-18530)
Hold reference of __bases__ tuple until tuple item is done with, because by
dropping the reference the item may be destroyed.
diff --git a/Lib/test/test_isinstance.py b/Lib/test/test_isinstance.py
index 65751ab..53639e9 100644
--- a/Lib/test/test_isinstance.py
+++ b/Lib/test/test_isinstance.py
@@ -251,6 +251,27 @@
# blown
self.assertRaises(RecursionError, blowstack, isinstance, '', str)
+ def test_issubclass_refcount_handling(self):
+ # bpo-39382: abstract_issubclass() didn't hold item reference while
+ # peeking in the bases tuple, in the single inheritance case.
+ class A:
+ @property
+ def __bases__(self):
+ return (int, )
+
+ class B:
+ def __init__(self):
+ # setting this here increases the chances of exhibiting the bug,
+ # probably due to memory layout changes.
+ self.x = 1
+
+ @property
+ def __bases__(self):
+ return (A(), )
+
+ self.assertEqual(True, issubclass(B(), int))
+
+
def blowstack(fxn, arg, compare_to):
# Make sure that calling isinstance with a deeply nested tuple for its
# argument will raise RecursionError eventually.