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gh-83731: Test that isinstance() ignores tuple subclass methods #158000

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Merged
methane merged 1 commit into from
Oct 16, 2026
+14 −0
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gh-83731: Test that isinstance() ignores tuple subclass methods #158000

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14 changes: 14 additions & 0 deletions Lib/test/test_isinstance.py
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Original file line number Diff line number Diff line change
Expand Up @@ -263,6 +263,20 @@ def test_subclass_tuple(self):
self.assertEqual(True, issubclass(int, (int, (float, int))))
self.assertEqual(True, issubclass(str, (str, (Child, str))))

def test_tuple_subclass_methods_not_called(self):
# gh-83731: make sure isinstance() reads the items of a tuple
# subclass directly, without calling its __iter__(),
# __getitem__() or __len__().
class T(tuple):
def __iter__(self):
raise AssertionError('__iter__ called')
def __getitem__(self, index):
raise AssertionError('__getitem__ called')
def __len__(self):
raise AssertionError('__len__ called')

self.assertTrue(isinstance(1, T((int,))))

@support.skip_if_huge_c_stack()
@support.skip_wasi_stack_overflow()
@support.skip_emscripten_stack_overflow()
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