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import matplotlib.pyplot as plt
import numpy as np

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

plt.figure()
plt.xlim((-1, 2))
plt.ylim((-2, 3))
new_sticks = np.linspace(-1, 2, 5)
plt.xticks(new_sticks)
plt.yticks([-2, -1.8, -1, 1.22, 3],
           [r'$really\ bad$', r'$bad$', r'$normal$', r'$good$', r'$really\ good$'])

#两个线条
l1=plt.plot(x, y1, label='linear line')
l2=plt.plot(x, y2, color='red', linewidth=1.0, linestyle='--', label='square line')
plt.legend(loc='upper right')#显示lable中对策内容并且显示在图的右上角


#分别重新设置线条对应的 label 
plt.legend(handles=[l1, l2], labels=['up', 'down'],  loc='best')


plt.show()

"""
'loc'参数: 'best' : 0,          
 'upper right'  : 1,
 'upper left'   : 2,
 'lower left'   : 3,
 'lower right'  : 4,
 'right'        : 5,
 'center left'  : 6,
 'center right' : 7,
 'lower center' : 8,
 'upper center' : 9,
 'center'       : 10,
"""