title: Python argparse: Make at least one argument required
body: <p>I've been using <code>argparse</code> for a Python program that can <code>-process</code>, <code>-upload</code> or both:</p>
  
  <pre><code>parser = argparse.ArgumentParser(description='Log archiver arguments.')
  parser.add_argument('-process', action='store_true')
  parser.add_argument('-upload',  action='store_true')
  args = parser.parse_args()
  </code></pre>
  
  <p>The program is meaningless without at least one parameter. How can I configure <code>argparse</code> to force at least one parameter to be chosen?</p>
  
  <p><strong>UPDATE:</strong></p>
  
  <p>Following the comments: What's the Pythonic way to parametrize a program with at least one option?</p>