<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def send_message(self, message):
 """Send a D-BUS message. The *message* argument must be ``gruvi.txdbus.DbusMessage`` instance. """

        if not isinstance(message, txdbus.DbusMessage):
            raise TypeError('message: expecting DbusMessage instance (got {!r})',
                                type(message).__name__)
        self._name_acquired.wait()
        if self._error:
            raise compat.saved_exc(self._error)
        elif self._transport is None:
            raise DbusError('not connected')
        self._writer.write(message.rawMessage)