Использовать NumPy * NDArray class и синтаксис синтаксис.
import numpy as np
my_array = np.zeros([256, 256, 450]) # 256x256x450 array
... # Do whatever you want to do to load data in
x_slice = my_array[0,:,:] # A 256x450 array, the first element in x
y_slice = my_array[:,0,:] # A 256x450 array, the first element in y
y_slice = my_array[:,99,:] # A 256 x 450 array, the 100th element in y