Matplotlib double Y axis + adjust legend position

from matplotlib.pyplot import rcParams 
import numpy as np
import matplotlib.pyplot as plt
import pandas as pd
import matplotlib

# Import data 、 Processing data （ This step can be ignored by readers ）
dataframe = pd.read_csv('D:/ Epidemic forecast /USA.csv',usecols=[1])#658 strip 
dataset_old = dataframe.values
diff1=[]
diff1=dataset_old .diff()
#  Prevent Chinese miscoding 
rcParams['font.sans-serif'] = 'kaiti'
#  Generate a time series  
time =pd.to_datetime(np.arange(0,658), unit='D',
                    origin=pd.Timestamp('2020-1-21'))
#  Create a canvas 
fig=plt.figure(figsize=(18,6))#figsize For canvas size 
#  Add a sub view on the canvas 
ax1=fig.add_subplot(111)
ax1.plot(time,dataset_old,color='#1bb9f6',linestyle='--')
ax1.set_title(' The cumulative number of infections in the United States and the number of new infections per day ',fontsize=20)
ax1.set_xlabel(' date / God ',fontsize=20)# Set up x Axis 
ax1.set_ylabel(' Cumulative number of infections / Ten million ',fontsize=20)# Set the left side y Axis 

ax2=ax1.twinx()# Very important 
ax2.plot(time,diff1,color='#9d5dfc',linestyle='-')
ax2.set_ylabel(' New infections per day / people ',fontsize=20)# Set the... On the right y Axis 

fig.legend([" Cumulative number of confirmed cases ",' New infections per day '],fontsize=20,loc='upper left',bbox_to_anchor=(0.13,0.9))
#loc Is the legend position ,bbox_to_anchor(n1,n2),n1 Move left and right ,n2 Move up and down , Manually adjust the legend position 

give the result as follows