title: How to capture mouse events on an arbitrary QWidget?
body: <p>I'm building a GUI with <code>Python</code> and <code>Qt</code>. The standard widgets are quite useful and work out of the box. However, I have some ideas about mouse gestures. More precisely, a button or label or text, that, after being clicked ant the mouse held pressed, moving the mouse around around has special effects.</p>
  
  <p>What is necessary to add mouse support for the following events </p>
  
  <ul>
  <li>mouse clicked over widget A while it was visible   </li>
  <li>mouse moved to x, y (at real time) </li>
  <li>mouse released  </li>
  </ul>
  
  <p>to an arbitrary widget?</p>
  
  <hr>
  
  <p>Right now I am trying to do this by class <code>A</code>, which inherits <code>QAbstractItemView</code> and owns a <code>QWidget</code>. However, nothing works AND </p>
  
  <blockquote>
    <p>NotImplementedError: QAbstractItemView.verticalOffset() is abstract and must be overridden</p>
  </blockquote>