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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def ExamineEvent(self, mediator, event):
 """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. """

    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)