<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def event_handler(self):
 """Wait on queue for listening to the events."""


        if not self._notify_queue:
            LOG.error('event_handler: no notification queue for %s',
                      self._service_name)
            return

        LOG.debug('calling event handler for %s', self)
        self.start()
        self.wait()