title: defaultdict with a parameter to the class constructor
body: <p>[Python 3.1]</p>
  
  <p>I want <code>defaultdict(int)</code>, except I'd like the default value to be <code>1</code> rather than <code>0</code>.</p>
  
  <ol>
  <li>Is there any neat way to do that? </li>
  <li>Should I do that?</li>
  </ol>