帮忙看看代码哪错了，会报错
fig.add_subplot(333)
n=20
Z=np.ones(n)
Z[-1]*=2
plt.pie(Z,explode=Z*0.05,colors=['%f' % (i/float(n)) for i in range(n)],
labels=('%.2f' % (i / float(n)) for i in range(n)))
plt.gca().set_aspect('equal')
plt.xticks([]),plt.yticks([])
plt.show()
TypeError: object of type 'generator' has no len()
