Method __missing__

Lib/test/test_dict.py:839–840

(self, key)

        # (G) subclass doesn't define __missing__ at all
        class D(dict):
            def __missing__(self, key):
                return 42
        d = D({1: 2, 3: 4})
        self.assertEqual(d[1], 2)
        self.assertEqual(d[3], 4)