<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def changes(self):
 """ Return a tuple with the removed and added facts since last run. """

        try:
            return self.added, self.removed
        finally:
            self.added = list()
            self.removed = list()