如果使用odoo上的函数？

Question

如果在数量上如何使用，如果数量＆lt; = 0则会被警告＆＃34;缺货＆＃34;。

from openerp.osv import fields,osv
import time
from datetime import datetime,timedelta


class hd_product(osv.osv):

_name="hd.product"
_description="Data of Products"

def _auto_qty(self, cr, uid, ids, qty, arg, context=None):
    records = self.browse(cr, uid, ids, context=context)
    result = {}
    for product in self.browse(cr, uid, ids, context=context):
        qty=0
        qty = product.income-product.outcome
        result[product.id] = qty
    return result

def _auto_income(self, cr, uid, ids, income, arg, context=None):
    result = {}
    for product in self.browse(cr, uid, ids, context=context):
        income = 0
        for buy in product.buy_line_ids:
            income += buy.qty
        result[product.id] = income
    return result

def _auto_outcome(self, cr, uid, ids, outcome, arg, context=None):
    result = {}
    for product in self.browse(cr, uid, ids, context=context):
        outcome = 0
        for sale in product.sale_line_ids:
            outcome += sale.qty
        result[product.id] = outcome
    return result

_columns={

    'name':fields.char('Product', size=30),
    'price':fields.float('Price', size=64),
    'qty':fields.function(_auto_qty, type='integer',method='true', string='Quantity'),
    'income':fields.function(_auto_income, type='integer', method='true', string='Income'),
    'outcome':fields.function(_auto_outcome, type='integer', method='true', string='Outcome'),
    'sale_line_ids':fields.one2many('hd.sale.line', 'product_id', 'Name'),
    'buy_line_ids':fields.one2many('hd.buy.line', 'product_id', 'Name'),

}