title: convert nested lists to string
body: <p>How can I convert the following <code>list</code> to a <code>string</code>?</p>
  <pre><code>list1= [[1, '1', 1], [2,'2',2], [3,'3',3]]
  
  Result: '1 1 1'
          '2 2 2'
          '3 3 3'
  </code></pre>
  <p>Thanks</p>