i'am added four fields in a view start,end,ignore and range 
range field is computed from start and end field and sometimes using ignore to pop up a record 
the method is working well but while importing data into a mode from excel sheet  range field isn't computed 
this the whole code​

class relate(models.Model):
    _name = 'relate'
    _rec_name = 'car'

    @api.multi
    @api.onchange('start', 'end', 'ignore')
    def years_rang(self):
        for rec in self:
            if rec.start and rec.end:
                record = [int(x) for x in range(int(rec.start), int(rec.end) + 1)]
                list = []
                if rec.ignore:
                    try:
                        record.remove(int(self.ignore))
                        list = []
                    except ValueError:
                        return {'warning': {'title': 'Warning!', 'message': "the Ignored year doesn't in range"}}
                for item in record:
                    range_id = self.env['yearrange'].create({'name': str(item)})
                    list.append(range_id.id)
                rec.rang = [(4, x, None) for x in list]
            pass
start = fields.Char(string="", required=False, )
end = fields.Char(string="", required=False, )
rang = fields.One2many(comodel_name="yearrange", inverse_name="product_id",store=True, string="Years" ,)
ignore = fields.Char(string="Ignore", required=False, ) 


class yearrange(models.Model):
    _name = 'yearrange'
    _rec_name = 'name'
    name = fields.Char()
    product_id = fields.Many2one(comodel_name="relate")