title: What is the fastest way to insert elements diagonally in 2D numpy array?
body: <p>Suppose we have a 2D numpy array like:</p>
  
  <pre><code>matrix = [[1, 2, 3],
            [4, 5, 6],
            [7, 8, 9],
            [10, 11, 12]]
  </code></pre>
  
  <p>I want to insert a value say 0 diagonally such that it becomes:</p>
  
  <pre><code>matrix = [[0, 1, 2, 3],
            [4, 0, 5, 6],
            [7, 8, 0, 9],
            [10, 11, 12, 0]]
  </code></pre>
  
  <p>What is the fastest way to do that?</p>