code: async def on_raw_433(self, message):
          
          if not self.registered:
              self._registration_attempts += 1
              # Attempt to set new nickname.
              if self._attempt_nicknames:
                  await self.set_nickname(self._attempt_nicknames.pop(0))
              else:
                  await self.set_nickname(
                      self._nicknames[0] + '_' * (self._registration_attempts - len(self._nicknames)))
docs: Nickname in use.