title: Python: Transpose over the secondary diagonal
body: <p>If I have this matrix, for example:</p>
  
  <pre><code>matrix = [[1, 2, 3, 4], 
            [5, 6, 7, 8], 
            [9, 10, 11, 12],
            [13, 14, 15, 16]]
  </code></pre>
  
  <p>And I want to transpose it over the secondary diagonal, without touching the first row and first column. It would look like this:</p>
  
  <pre><code>matrix = [[1, 2, 3, 4], 
            [5, 16, 12, 8], 
            [9, 15, 11, 7],
            [13, 14, 10, 6]]
  </code></pre>
  
  <p>This is what I've tried, but it doesn't change the matrix:</p>
  
  <pre><code>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
  </code></pre>