code: def watch_prefix_once(self, key_prefix, timeout=None, **kwargs):
          
          kwargs['range_end'] = \
              utils.increment_last_byte(utils.to_bytes(key_prefix))
          return self.watch_once(key_prefix, timeout=timeout, **kwargs)
docs: Watches a range of keys with a prefix and stops after the first event.
  
          If the timeout was specified and event didn't arrived method
          will raise ``WatchTimedOut`` exception.