参考：python中三个点（…）

　　三个点表示 numpy 数组中的省略冒号，就是全部包括的省略

　　例如 a[:, :, :, :-1] 等价于 a[..., :-1]

　　对于多维度数组的操作会略显方便

>>> import numpy as np
>>> a = np.arange(24).reshape(2, 2, 2, 3)
>>> a
array([[[[ 0,  1,  2],
         [ 3,  4,  5]],

        [[ 6,  7,  8],
         [ 9, 10, 11]]],


       [[[12, 13, 14],
         [15, 16, 17]],

        [[18, 19, 20],
         [21, 22, 23]]]])
>>> a[...,:-1]
array([[[[ 0,  1],
         [ 3,  4]],

        [[ 6,  7],
         [ 9, 10]]],


       [[[12, 13],
         [15, 16]],

        [[18, 19],
         [21, 22]]]])
>>> a[:,:,:,:-1]
array([[[[ 0,  1],
         [ 3,  4]],

        [[ 6,  7],
         [ 9, 10]]],


       [[[12, 13],
         [15, 16]],

        [[18, 19],
         [21, 22]]]])