title: argparse change definition of argument
body: <p>I set up my argument parser as follows:</p>
  
  <pre><code>parser=argparse.ArgumentParser()
  parser.add_argument('--point',help='enter a point (e.g. 2,3,4)')
  parser.parse_args('--point=-2,5,6'.split())  #works
  parser.parse_args('--point -2,5,6'.split())  #doesn't work :(
  </code></pre>
  
  <p>Is there any way to tell argparse that strings which match the regular expression <code>r"-\d+.*"</code> are not options but an argument of an option?</p>
  
  <p>Also note that I <em>could</em> do something like this:</p>
  
  <pre><code>parser.add_argument('--point',nargs='*')
  parser.parse_args('--point -2 5 6'.split())
  </code></pre>
  
  <p>but that's not really how I want it to work.</p>