You can provide a link to the controller below, instructing the user to right click on it and then select 'save link as...', he can store the response in any selected directory using his choice of filename (a name ending in .csv):
def tocsv(): response.headers['content-type']='text/csv' rr=db((db.autos.dt>=t1) & (db.autos.dt<=t2)).select(orderby=~db.autos.dt) return '\n'.join([','.join(map(str,[r.id, r.num, r.ves, r.dt, r.usr])) for r in rr])
