s = pd.Series([5, 5, 6, 7, 5, 5, 5])
>>> s.rolling(3).std()
0             NaN
1             NaN
2    5.773503e-01
3    1.000000e+00
4    1.000000e+00
5    1.154701e+00
6    2.580957e-08
dtype: float64