test_userdict.py 文件源码

def test_missing(self):
        # Make sure UserDict doesn't have a __missing__ method
        self.assertEqual(hasattr(collections.UserDict, "__missing__"), False)
        # 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 a all
        class D(collections.UserDict):
            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(collections.UserDict):
            def __missing__(self, key):
                raise RuntimeError(key)
        e = E()
        try:
            e[42]
        except RuntimeError as err:
            self.assertEqual(err.args, (42,))
        else:
            self.fail("e[42] didn't raise RuntimeError")
        class F(collections.UserDict):
            def __init__(self):
                # An instance variable __missing__ should have no effect
                self.__missing__ = lambda key: None
                collections.UserDict.__init__(self)
        f = F()
        try:
            f[42]
        except KeyError as err:
            self.assertEqual(err.args, (42,))
        else:
            self.fail("f[42] didn't raise KeyError")
        class G(collections.UserDict):
            pass
        g = G()
        try:
            g[42]
        except KeyError as err:
            self.assertEqual(err.args, (42,))
        else:
            self.fail("g[42] didn't raise KeyError")