np.newaxis的作用就是在这一位置增加一个一维，这一位置指的是np.newaxis所在的位置，比较抽象，需要配合例子理解。
x1 = np.array([1, 2, 3, 4, 5]) # the shape of x1 is (5,) x1_new = x1[:, np.newaxis] # now, the shape of x1_new is (5, 1) # array([[1], # [2], # [3], # [4], # [5]]) x1_new = x1[np.newaxis,:] # now, the shape of x1_new is (1, 5) # array([[1, 2, 3, 4, 5]])
再来一个例子
In [124]: arr = np.arange(5*5).reshape(5,5) In [125]: arr.shape Out[125]: (5, 5) # promoting 2D array to a 5D array In [126]: arr_5D = arr[np.newaxis, ..., np.newaxis, np.newaxis] In [127]: arr_5D.shape Out[127]: (1, 5, 5, 1, 1)
转自：https://www.jianshu.com/p/78e1e281f698