[web2py] IS_IN_DB label from two tables

[niknok]

The following validator doesn't work: 

    IS_IN_DB(db(db.g_province.id==db.g_municipality.province)\
                        ,db.g_municipality.psgc_m\
                        ,label='%(g_municipality.name)s (%(g_province.name)s)')


I am trying to generate a select option that shows a label consisting of
the g_province.name and g_municipality.name fields. How do I do that?

Thanks.
/r
Nik