from math import pi
nr.seed(2021)
dates = pd.date_range(start = '1-31-2001', end = '1-31-2021', freq = 'M')
periodic = pd.Series([2 * sin(pi*x/6) for x in range(len(dates))],
                    index = dates)
periodic = periodic + nr.normal(size = len(dates))
plot_ts(periodic, 'periodic series with noise')
splt.plot_acf(periodic, lags = 40)
splt.plot_pacf(periodic, lags = 40)
plt.show()