code: def ExamineEvent(self, mediator, event):
      
      if event.data_type not in self._DATATYPES:
        return
  
      url = getattr(event, 'url', None)
      if url is None:
        return
      parsed_url = urlparse.urlparse(url)
      domain = getattr(parsed_url, 'netloc', None)
      if domain in self._domains:
        # We've already found an event containing this domain.
        return
      self._domains.append(domain)
docs: Analyzes an event and extracts domains from it.
  
      We only evaluate straightforward web history events, not visits which can
      be inferred by TypedURLs, cookies or other means.
  
      Args:
        mediator (AnalysisMediator): mediates interactions between
            analysis plugins and other components, such as storage and dfvfs.
        event (EventObject): event to examine.