数组中[::-1]或[::-n]的区别，如三维数组[：，：：-1，：]

import numpy as np
a=np.array([[11,12,13,14,15,16,17,18],[21,22,23,24,25,26,27,28],[31,32,33,34,35,36,37,38],[41,42,43,44,45,46,47,48]])
print(a)
b=a[:,::-1]    #表示从最后一列开始，每隔1列就取，相当于倒叙

print(b)

b1=a[:,::-2]   #表示从最后一列开始，每隔2列就取
print(b1)
b2=a[:,::-4]
print(b2)
c=a[::-1,:]
print(c)
d=a[::-1,::-1]
print(d)