title: How to create argument of type "list of pairs" with argparse?
body: <p>I need to let the end user of my python script types something like:</p>
  
  <pre><code>script.py -sizes &lt;2,2&gt; &lt;3,3&gt; &lt;6,6&gt;
  </code></pre>
  
  <p>where each element of the <code>-sizes</code> option is a pair of two positive integers. How can I achieve this with <code>argparse</code> ?</p>