title: Write two-dimensional list to JSON file
body: <p>I have a two-dimensional list like:</p>
  
  <pre><code>data = [[1,2,3], [2,3,4], [4,5,6]]
  </code></pre>
  
  <p>I want to write it to JSON file like this:</p>
  
  <pre><code>{
      'data':[
          [1,2,3],
          [2,3,4],
          [4,5,6]
      ]
  }
  </code></pre>
  
  <p>I get this with: <code>json.dumps(data, indent=4, sort_keys=True)</code>:</p>
  
  <pre><code>{
      'data':[
          [
           1,
           2,
           3
          ],
          [
           2,
           3,
           4
          ],
          [
           4,
           5,
           6]
      ]
  }
  </code></pre>
  
  <p>Here is anther question <a href="https://stackoverflow.com/questions/13249415/how-to-implement-custom-indentation-when-pretty-printing-with-the-json-module">How to implement custom indentation when pretty-printing with the JSON module?</a>, but that's dictionaries.</p>