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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def complete_event(self, event_id: str):
 """Complete the specified event."""

        event_ids = DB.get_list(self._processed_key)
        if event_id not in event_ids:
            raise KeyError('Unable to complete event. Event {} has not been '
                           'processed (ie. it is not in the processed '
                           'list).'.format(event_id))
        DB.remove_from_list(self._processed_key, event_id, pipeline=True)
        key = _keys.completed_events(self._object_type, self._subscriber)
        DB.append_to_list(key, event_id, pipeline=True)
        DB.execute()