我试图按照以下说明进行操作：http :
//wiki.scipy.org/Cookbook/Matplotlib/Animations

为什么下面的代码没有显示预期的行为？（请参阅代码中有关预期和观察到的注释）

import matplotlib.pyplot as plt
from pylab import rand

f, ax = plt.subplots()

# Generate dummy plot
ax.set_xlim([0, 10])
ax.set_ylim([0, 10])
ax.imshow(rand(10,10),  interpolation='nearest')
# Until here it works
# If i would add a 
#     f.show() 
# i would see the image

# Save figure
canvas = ax.figure.canvas
background = canvas.copy_from_bbox(ax.bbox)

# Clear Axes
ax.cla()

# try to restore figure
canvas.restore_region(background)
f.show()

# Unfortunatly I only see an empty figure now, Why??

后续问题：

• 我打算background在同一轴上的已修改位置上生成的半透明副本。（这怎么可能？