import unittest class TestLoadAttrCache(unittest.TestCase): def test_descriptor_added_after_optimization(self): class Descriptor: pass class C: def __init__(self): self.x = 1 x = Descriptor() def f(o): return o.x o = C() for i in range(1025): assert f(o) == 1 Descriptor.__get__ = lambda self, instance, value: 2 Descriptor.__set__ = lambda *args: None self.assertEqual(f(o), 2)