title: Python argparse: separate options for positional arguments
body: <p>i write a script that takes one or more input files. I want to be able to specify  options for the script (A and B) and for each of the input files separately (C and D).</p>
  
  <p>Usage should look like: </p>
  
  <pre><code>script.py [-A] [-B]  [-C] [-D] file1 [[-C] [-D] file2] ...
  </code></pre>
  
  <p>How can it be done with <code>argparse</code>?</p>
  
  <p>Thank you!</p>