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(n):
            df = pd.DataFrame({'A': np.arange(n), 'B': np.arange(n) + 1.0})
            df1 = df[df.A > 5]
            return len(df1.B)