title: How to create an abstract base class in python which derived from QObject
body: <p>I'm trying to create an abstract base class for an interface, but I need it to derive from QObject for signals and slots. My class definition looks like this:</p>
  
  <pre><code>import abc
  from PyQt5.QtCore import QObject
  
  class interface_class(abc.ABC, QObject):
      pass
  </code></pre>
  
  <p>It fails with:</p>
  
  <pre><code>TypeError: metaclass conflict: the metaclass of a derived class must be a (non-strict) subclass of the metaclasses of all its bases
  </code></pre>
  
  <p>Any ideas?</p>
  
  <p>thanks</p>