Class F

Lib/test/test_select.py:89–92

    def test_select_mutated(self):
        a = []
        class F:
            def fileno(self):
                del a[-1]
                return sys.__stdout__.fileno()
        a[:] = [F()] * 10
        self.assertEqual(select.select([], a, []), ([], a[:5], []))