Python如何根据时间序列数据作图

import pandas as pd
import matplotlib.pyplot as plt
import datetime
 
df = pd.read_csv('no09.csv')
t = df.iloc[0:200, 0]
t = [datetime.datetime.strptime(i, '%Y/%m/%d') for i in t]
co2 = [float(i) for i in df.iloc[0:200,1]]
he = [float(i) for i in df.iloc[0:200,2]]
plt.subplot(211)
plt.plot(t, co2, 'o-')
plt.xlabel('Date [Year/Month')
plt.ylabel('CO2 / %')
plt.grid(ls = '--')
plt.subplot(212)
plt.plot(t, he, 'o-')
plt.xlabel('Date [Year/Month]')
plt.ylabel('He /ppm')
plt.annotate('2002/07/07 165ppm', xy = (datetime.datetime.strptime(('2002/07/07'), '%Y/%m/%d'), 165),
       xytext = (datetime.datetime.strptime(('2002/08/01'), '%Y/%m/%d'), 123),
       arrowprops = dict(facecolor = 'black', shrink = 0.05, width = 2, headwidth = 6,
                headlength = 6))
plt.grid(ls = '--')
plt.show()