def traverse(self, obj):

        def replace(elem):
            for v in self._visitor_iterator:
                e = v.replace(elem)
                if e is not None:
                    return e
        return replacement_traverse(obj, self.__traverse_options__, replace)
traverse and visit the given expression structure.
dataset/ETHPy150Open RoseOu/flasky/venv/lib/python2.7/site-packages/sqlalchemy/sql/visitors.py/ReplacingCloningVisitor.traverse