Method test_missing

Lib/test/test_dict.py:829–870

(self)

        self.assertEqual({2} | {1:1}.items(), {(1,1), 2})

    def test_missing(self):
        # Make sure dict doesn't have a __missing__ method
        self.assertNotHasAttr(dict, "__missing__")
        self.assertNotHasAttr({}, "__missing__")
        # Test several cases:
        # (D) subclass defines __missing__ method returning a value
        # (E) subclass defines __missing__ method raising RuntimeError
        # (F) subclass sets __missing__ instance variable (no effect)
        # (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)
        self.assertNotIn(2, d)
        self.assertNotIn(2, d.keys())
        self.assertEqual(d[2], 42)

        class E(dict):
            def __missing__(self, key):
                raise RuntimeError(key)
        e = E()
        with self.assertRaises(RuntimeError) as c:
            e[42]
        self.assertEqual(c.exception.args, (42,))

        class F(dict):
            def __init__(self):
                # An instance variable __missing__ should have no effect
                self.__missing__ = lambda key: None
        f = F()
        with self.assertRaises(KeyError) as c:
            f[42]
        self.assertEqual(c.exception.args, (42,))

        class G(dict):
            pass
        g = G()
        with self.assertRaises(KeyError) as c:
            g[42]
        self.assertEqual(c.exception.args, (42,))

    def test_tuple_keyerror(self):
        # SF #1576657