def save(self, filename=None):
        filename = Path(filename) if filename is not None else self.filename
        with filename.open("w") as f:
            f.write(self.yaml)
def test_impl():
            A = np.array([1., 2., 3.])
            A[0] = 4.0
            df = pd.DataFrame({'A': A})
            return df.A.var()