title: Add arguments based on the value of another argument
body: <p>Based on one of the inputs, I would like to initialize certain objects. The values from these objects will be the default values for rest of the arguments. So i need the value of one of the argument even before parser.parse_args(). How can i achieve this with python argparse module. All the options will be given as one command line.</p>
  
  <p>The default values should be shown with help. These values come from object.</p>
  
  <pre><code>def cli():
      option1 = None
      parser = argparse.ArgumentParser()
      parser.add_argument('--option1', help=argparse.SUPPRESS)
      #option1 = value from --option1
      abc(option1)
      parser.add_argument('--option2', default=abc.getValue())
      args = parser.parse_args()
  </code></pre>
  
  <p>How can i achieve this? </p>