def __missing__(self, key):
        if self.default_factory is None:
            raise KeyError(key)
        else:
            ret = self[key] = self.default_factory(name=key)
            return ret
def test_impl():
            A = np.array([1., 2., 3.])
            A[0] = 4.0
            df = pd.DataFrame({'A': A})
            return df.A.std()