<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def promote(self):
 """ Mark object as alive, so it won't be collected during next run of the garbage collector. """

        if self.expiry is not None:
            self.promoted = self.time_module.time() + self.expiry