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

 """Remove editors that are not longer open."""

        self._update_id_list()
        for _id in self.history[:]:
            if _id not in self.id_list:
                self.history.remove(_id)