def clean(self):
        if ((self.user_id is not None)
            and (self.device_name in
                 [d.device_name for d in self.user.device_set.all()
                  if d.id != self.id])):
                raise ValidationError('Device name already taken')
        if (self.device_ip is None):
            self.device_ip = getNewIPAddress()