def calculate_cost(items, d):
    #items = list of dictionery {SKUID, qty}, d = costing date
    p = current.db((current.db.Product_Costing.valid_from <= d) & (current.db.Product_Costing.valid_to >= d)).select(current.db.Product_Costing.SKUID, current.db.Product_Costing.mat_cost, current.db.Product_Costing.log_cost)

    if len(p) < 1:
        raise ValueError('Error: No cost to calculate. (Items not exist or date out of range?)')

    total_mat_cost = 0
    total_log_cost = 0
    for i in items:
        unpackable_item = get_unpackable_item()
        if int(i['SKUID']) in unpackable_item:
            pass
        else:
            current_p = p.find(lambda row: row.SKUID == int(i['SKUID'])).first()

            total_mat_cost = total_mat_cost + (current_p.mat_cost * float(i['qty']))
            total_log_cost = total_log_cost + (current_p.log_cost * float(i['qty']))

    return total_mat_cost, total_log_cost