New Axis

import numpy as np

x1 = np.arange(1,10).reshape(3,3)

x1

array([[1, 2, 3],
       [4, 5, 6],
       [7, 8, 9]])

print(x1.shape)

(3, 3)

x1_new = x1[:,np.newaxis]

print(x1_new.shape)

(3, 1, 3)

x1_new

array([[[1, 2, 3]],

       [[4, 5, 6]],

       [[7, 8, 9]]])