<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def _content_function(self):
 """ This returns a set containing the actively shown module. This is so we only get update events triggered for these modules. """

        # ensure that active is valid
        self.active = self.active % len(self.items)

        return set([self.items[self.active]])