np.mean()
搬运 :https://blog.csdn.net/lilong117194/article/details/78397329?depth_1-utm_source=distribute.pc_relevant.none-task&utm_source=distribute.pc_relevant.none-task
>>> a = np.array([[1, 2], [3, 4]])
>>> a
array([[1, 2],
[3, 4]])
>>> np.mean(a)
2.5
>>> np.mean(a, axis=0) # axis=0，计算每一列的均
