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(n):
            df = pd.DataFrame({'A': np.arange(n), 'B': np.random.ranf(n)})
            Ac = df.A.rolling(3).sum()
            return Ac.sum()