title: Python argParse change string to a different type
body: <p>I am asking user to input a string before running my python program.</p>
  
  <pre><code>ASK = 'ASK'
  BID = 'BID'
  parser.add_argument('-s', "--side", dest = 'side', help = "side", nargs = 1, 
      required = True, choices = ['ASK','BID'])
  side = args.side[0] 
  print side
  &gt;&gt;"ASK"
  </code></pre>
  
  <p>I want to assign <code>side</code> to <code>ASK</code> or <code>BID</code> variables
  I know I can do it this way:</p>
  
  <pre><code>if side == 'ASK':
      side = ASK
  else: 
      side = BID
  </code></pre>
  
  <p>I was wondering if I can change <code>args.side[0]</code> to a specific variable ASK or BID within parser.add_argument.</p>
  
  <p>Thanks</p>