title: how to modify nargs( of optparse-add_option) from User input(raw_input)?
body: <p>This Question is continuation of old question @: <a href="https://stackoverflow.com/questions/24285311/how-to-access-nargs-of-optparse-add-action">how to access nargs of optparse-add_action?</a></p>
  
  <p>As that question was answered for what it was in-tented.</p>
  
  <p><strong>Brief:</strong></p>
  
  <p>Suppose if I am using add_option utility like below:</p>
  
  <pre><code>parser.add_option('-c','--categories', dest='Categories', nargs=4 )
  </code></pre>
  
  <p>Is there a way to modify <code>nargs</code> of <code>add_option()</code> from user input using <code>raw_input</code>.?</p>
  
  <p><strong>EDIT:</strong>
  I will give a clear difference between my "previous question need" and "this question need".</p>
  
  <p><em>First question case:</em></p>
  
  <p>My script will ask for user inputs if user has provided no inputs, i.e.,He has just run</p>
  
  <pre><code>#./commandparser.py
  </code></pre>
  
  <p><em>Second Question case requirement is:</em></p>
  
  <p>when i run my script ./commandparser.py -c abc bac cad
  it throws error: <code>commandparser.py: error: -c option requires 4 arguments</code> and exit the script.</p>
  
  <p>Instead of throwing error and exit the script. I want some mechanism so that it asks user to input remaining arguments i.e., 4th argument without exiting the script.</p>