If you just need the last row from your (ordered) select object, you can just add ".last()" to the end of your query:
db(db.operations.date.month() == current_month).select(db. operations.date,db.operations.budget,db.operations.title,db.operations.amount,groupby=db.operations.budget,orderby= ~db.operations.date|~db.operations.id).last()
