matplotlib 和 Matlab 差不多，而且不需要 hold on 语句。例如

 import matplotlib.pyplot as plt

x = range(10)
y1 = [elem*2 for elem in x]
plt.plot(x, y1)

y2 = [elem**2 for elem in x]
plt.plot(x, y2, 'r--')

plt.show()