legend图例

import matplotlib.pyplot as plt
import numpy as np

x=np.linspace(-3,3,50)
y1=x*2+1
y2=x**2
plt.plot(x,y1)

plt.figure(num=3,figsize=(8,5))
plt.plot(x,y2)
plt.plot(x,y1,color="red",linewidth=1.0,linestyle="--")

plt.xlim((-1,2))
plt.ylim((-2,3))
plt.xlabel("I am x")
plt.ylabel("I am y")

new_ticks=np.linspace(-1,2,5)
print(new_ticks)
plt.xticks(new_ticks)
plt.yticks([-2,-1.8,-1,1.22,3,],
        [r'$really bad$',r'$bad alpha$',r'$normal$',r'$good$','$really good$'])

l1, = plt.plot(x,y2,label='up')
l2, = plt.plot(x,y1,color='red',linewidth=1.0,linestyle='--',label='down')
plt.legend(handles=[l1,l2,],labels=['aaa','bbb'],loc='best')

plt.show()