def update_item(db, klass, item_id, newvalues):
    """Update database item 
       :argument: db database SQLalchemy connection session 
       :argument: klass class representing table objects
       :argument: item_id the id for row to update
       :argument: newvalues a dictionary with the column keys, values to be updated
       :return nothing
    """
    db.query(klass).filter_by(id=item_id).update(newvalues)
    db.commit()
    return
