title: __setattr__ only when attribute does not exist
body: <p>If one overrides the magic method <code>__getattr__</code> in a class, the overridden method is called only when the attribute is not found, otherwise default behavior occurs.</p>
  
  <p>But this does not seem to be the case with <code>__setattr__</code>, it affects all attributes.</p>
  
  <p>What I am looking for is something which behaves normally when the attribute exists and follows some custom code when the attribute does not exist. And how does one call <code>super</code> on <code>__setattr__</code> ? </p>