title: Transpose list of lists
body: <p>Let's take:</p>
  <pre><code>l = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]
  </code></pre>
  <p>The result I'm looking for is</p>
  <pre><code>r = [[1, 4, 7], [2, 5, 8], [3, 6, 9]]
  </code></pre>
  <p>and not</p>
  <pre><code>r = [(1, 4, 7), (2, 5, 8), (3, 6, 9)]
  </code></pre>