def _reconnect_delay(self):
        """ Calculate reconnection delay. """
        if self.RECONNECT_ON_ERROR and self.RECONNECT_DELAYED:
            if self._reconnect_attempts >= len(self.RECONNECT_DELAYS):
                return self.RECONNECT_DELAYS[-1]
            else:
                return self.RECONNECT_DELAYS[self._reconnect_attempts]
        else:
            return 0
Calculate reconnection delay.