<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def lock(self, seconds=5):

 """
 Lock the device for a certain period of time. iOS only.
 """

        self._current_application().lock(robot.utils.timestr_to_secs(seconds))