code: def _process_events(self, events):
          
          for f, callback, transferred, key, ov in events:
              try:
                  self._logger.debug('Invoking event callback {}'.format(callback))
                  value = callback(transferred, key, ov)
              except OSError:
                  self._logger.warning('Event callback failed', exc_info=sys.exc_info())
              else:
                  f.set_result(value)
docs: Process events from proactor.