title: How to fix pylint warning "Abstract class not referenced"?
body: <p>I have a Python class that raises "NotImplementedError" for a couple of methods and the class is inherited by a few other classes which are defined in their own files.</p>
  
  <p>When I run Pylint on the file that has the abstract class, it always complains "Abstract class not referenced". I was wondering is it just Pylint being paranoid or there's actually something I do need to fix?</p>