<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def request(self, target="candidate"):
 """Allows the client to lock the configuration system of a device. *target* is the name of the configuration datastore to lock """

        node = new_ele("lock")
        sub_ele(sub_ele(node, "target"), target)
        return self._request(node)