<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def DbUnExportDevice(self, argin):
 """ Mark a device as non exported in database :param argin: Device name :type: tango.DevString :return: :rtype: tango.DevVoid """

        self._log.debug("In DbUnExportDevice()")
        dev_name = argin[0].lower()
        self.db.unexport_device(dev_name)