Class MutatingCompare

Lib/test/test_deque.py:114–117

        d = deque([1, 2, 3])
        self.assertRaises(ArithmeticError, d.count, BadCompare())
        class MutatingCompare:
            def __eq__(self, other):
                self.d.pop()
                return True
        m = MutatingCompare()
        d = deque([1, 2, 3, m, 4, 5])
        m.d = d