matplotlib怎么画圆？

import matplotlib.pyplot as plt
plt.figure(figsize=(4, 4))
plt.axis('equal')
ax = plt.gca()
ax.set_xlim((-2, 2))
ax.set_ylim((-2, 2))
disk1 = plt.Circle((0, 0), 1, color='r', fill=False)
ax.add_artist(disk1)
plt.show()