Python: Transpose over the secondary diagonal

Question

If I have this matrix, for example:

matrix = [[1, 2, 3, 4], 
          [5, 6, 7, 8], 
          [9, 10, 11, 12],
          [13, 14, 15, 16]]

And I want to transpose it over the secondary diagonal, without touching the first row and first column. It would look like this:

matrix = [[1, 2, 3, 4], 
          [5, 16, 12, 8], 
          [9, 15, 11, 7],
          [13, 14, 10, 6]]

This is what I've tried, but it doesn't change the matrix:

for i in range(1, 4):
    for j in range(1, 4):
        temp = copy.deepcopy(matrix[i][j])
        matrix[i][j] = matrix[4-j][4-i]
        matrix[4-j][4-i] = temp

Answer 1

Your code does not work because you are swapping TWO times each pair of variables, building again the same matrix.

Also, you don't need the copy.deepcopy call for a matrix of integers, and you reference a table variable which is undefined

# Working code
for i in range(1, 4):
    for j in range(1, 4 - i):
        matrix[i][j], matrix[4 - j][4 - i] = matrix[4 - j][4 - i], matrix[i][j]