为什么扩展模块的方法不工作？

floatingdudu

大神好！
我建了个简单的采购订单扩展模块，代码如下。
重启odoo后，没有报错，修改视图后在采购订单行中可以看到新增的这几个字段。但是方法没有执行：
product_qty&price_unit并按代码没有赋值。将下面的代码简单改为对myprice字段赋值或提示告警，方法一样没有反应。

'''
from datetime import datetime
from dateutil.relativedelta import relativedelta

from odoo import api, fields, models, SUPERUSER_ID, _
from odoo.tools import DEFAULT_SERVER_DATETIME_FORMAT
from odoo.tools.float_utils import float_compare
from odoo.exceptions import UserError, AccessError
from odoo.tools.misc import formatLang
from odoo.addons import decimal_precision as dp
from odoo.exceptions import ValidationError
from itertools import groupby

class PurchaseOrderLine(models.Model):
""" Defines purchase oder """
_inherit = ['purchase.order.line']

x_specification = fields.Char(related='product_id.prd_specification',string=u'规格')
x_standard_price = fields.Float(related='product_id.standard_price',string=u'标准单价')
myprice = fields.Float(string=u'标准单价1')

@api.onchange('product_id')
def onchange_product_id(self):
res = super(PurchaseOrderLine,
for rec in self:
rec.product_qty = 10 # will trigger _onchange_quantity() on return

return res

@api.onchange('product_qty', 'product_uom')
def _onchange_quantity(self):
res = super(PurchaseOrderLine, self)._onchange_quantity()
for rec in self:
rec.price_unit = 2.0