code: def subscribe(self, coro):
          
          if coro not in self._notify:
              self._notify.append(coro)
              return True
          return False
docs: Subscribe to status updates from the Opentherm Gateway.
          Can only be used after connect()
          @coro is a coroutine which will be called with a single
          argument (status) when a status change occurs.
          Return True on success, False if not connected or already
          subscribed.