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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 get_relation(self, rel_id, resolve_missing=False):
 """ Get a relation by its ID. :param rel_id: The relation ID :type rel_id: Integer :param resolve_missing: Query the Overpass API if the relation is missing in the result set. :return: The relation :rtype: overpy.Relation :raises overpy.exception.DataIncomplete: The requested relation is not available in the result cache. :raises overpy.exception.DataIncomplete: If resolve_missing is True and the relation can't be resolved. """

        relations = self.get_relations(rel_id=rel_id)
        if len(relations) == 0:
            if resolve_missing is False:
                raise exception.DataIncomplete("Resolve missing relations is disabled")

            query = ("\n"
                     "[out:json];\n"
                     "relation({relation_id});\n"
                     "out body;\n"
                     )
            query = query.format(
                relation_id=rel_id
            )
            tmp_result = self.api.query(query)
            self.expand(tmp_result)

            relations = self.get_relations(rel_id=rel_id)

        if len(relations) == 0:
            raise exception.DataIncomplete("Unable to resolve requested reference")

        return relations[0]