title: Argparse: Check if any arguments have been passed
body: <p>My script should start a demo mode, when the no parameters are given. I tried this:</p>
  
  <pre><code>args = parser.parse_args()
  if len(args) == 0:
      run_demo()
  else:
      # evaluate args
  </code></pre>
  
  <p>Which gives a <code>*** TypeError: object of type 'Namespace' has no len()</code> as <code>args</code> is no list. </p>
  
  <p>How would I achieve what I want?</p>