A partire da versione 1.1
puoi usare FunctionElement.within_group(*order_by)
:
In [7]: func.listagg(column('person'), ',').within_group(column('person'))
Out[7]: <sqlalchemy.sql.elements.WithinGroup object at 0x7f2870c83080>
In [8]: print(_.compile(dialect=oracle.dialect()))
listagg(person, :listagg_1) WITHIN GROUP (ORDER BY person)
