title: How to iterate over a list of lists and print items of each list as a comma-delimited string
body: <p>If I have a list of lists:</p>
  <pre><code>x = [['1','2','3'],['4','5','6'],['7','8','9']]
  </code></pre>
  <p>How do I iterate over these lists and print them to get the following output?</p>
  <pre class="lang-none prettyprint-override"><code>1, 2, 3
  4, 5, 6
  7, 8, 9
  </code></pre>