Class DefaultChainMap

Lib/test/test_collections.py:176–178

    def test_missing(self):
        class DefaultChainMap(ChainMap):
            def __missing__(self, key):
                return 999
        d = DefaultChainMap(dict(a=1, b=2), dict(b=20, c=30))
        for k, v in dict(a=1, b=2, c=30, d=999).items():
            self.assertEqual(d[k], v)                                  # check __getitem__ w/missing