code: def responseReceived(self, response, tag):
          
          self._queue.pop(tag).callback(response)
docs: Receives some characters of a netstring.
  
          Whenever a complete response is received, this method calls the
          deferred associated with it.
  
          @param response: A complete response generated by exiftool.
          @type response: C{bytes}
          @param tag: The tag associated with the response
          @type tag: C{int}