*）matplotlib animate中变量作用域的问题
错误提示：
UnboundLocalError: local variable ‘i‘ referenced before assignment
代码：
i=0
def animate(frameno):
x = mu + sigma * np.random.randn(N)
n, _ = np.histogram(x, bins, normed=True)
time_text.set_text(time_template%frameno)
i+=1
for rect, h in zip(patches, n):
rect.set_height(h)
return patches
原文：https://www.cnblogs.com/Gaoqiking/p/11258442.html