def _lookup_reverse_constraint(self, table_name, column_name=None):
        """Look for the column referenced by a foreign constraint"""
        db_name = self._get_setting('NAME')
        if self.dry_run:
            raise DryRunError("Cannot get constraints for columns.")

        if not self._is_valid_cache(db_name, table_name):
            # Piggy-back on lookup_constraint, ensures cache exists
            self.lookup_constraint(db_name, table_name)

        try:
            table = self._reverse_cache[db_name][table_name]
            if column_name == None:
                return [(y, tuple(y)) for x, y in table.items()]
            else:
                return tuple(table[column_name])
        except __HOLE__:
            return []
dataset/ETHPy150Open cloudera/hue/desktop/core/ext-py/South-1.0.2/south/db/mysql.py/DatabaseOperations._lookup_reverse_constraint