A.axis
axis is the specified axis.
A three-dimensional array can be regarded as a one-dimensional array whose elements are two-dimensional arrays, and a two-dimensional array can be regarded as a one-dimensional array whose elements are one-dimensional arrays. (It's comfortable to understand this way!)
Example:
axis=2 means that the three-dimensional array sums the innermost layer, that is, inside each one-dimensional array.
axis=0 is to sum the elements of the outermost layer.
Two.keepdim
It can be understood that the'keepdims = True' parameter is to keep the dimension of the result the same as the original array, that is, keep dimension keeps the dimension.
import numpy as np
b=np.arange(12)
b=b.reshape(2,6)
print(b)
print('b中的元素之和：',np.sum(b))
#即在b的第一个轴上进行加和，相当于压缩行，也可以理解为二维矩阵的第一层括号里的东西加和
#若axis=1则是压缩列，也就是对第二层括号里面的进行求和
sum=np.sum(b,axis=0,keepdims=True)
print(sum)
operation result:
[[ 0 1 2 3 4 5]
[ 6 7 8 9 10 11]]
b中的元素之和： 66
[[ 6 8 10 12 14 16]]The last output specifies axis=0, keepdim=True, you can see that the output is a two-dimensional array, if you don’t add keepdim=True, then the result is a one-dimensional array [6 8 10 12 14 16]