I have created an order form that contain a one2many list to identify the products featured in this order ,and i want to make a autoincrement field to reference the products inside the order form 
 for ex : an order may contain 3 products , the first will be number "1" ,the second   number"2" ... ,and i want it to be the same for every order
this is my .py file , but what i ve tried didn't work

#stapp

from openerp import models, fields

from odoo import api import xmlrpclib

server = "http://localhost:8069"

database = "test01"

usr = "malek"

pwd ="malek93/"

common = xmlrpclib.ServerProxy("{}/xmlrpc/2/common" .format(server))

uid = common.authenticate(database,usr,pwd, {})

odapi = xmlrpclib.ServerProxy("{}/xmlrpc/2/object" .format(server))

class bon_de_versement(models.Model):

     _name = 'bondeversement'

     imgg = fields.Binary(string="image" , filters=None)

     name = fields.Char("Nom Complet")

     prix = fields.Float(string="Prix",readonly=True, store=True, compute="_calcprix")

     date = fields.Date("Date de debut")

     note = fields.Text("Note")

    nutrient_ids = fields.One2many('versement', 'product_id' , 'Nutrient')

     article_ids = fields.One2many('bondeversement.article', 'product_id' , 'Article')

     reste = fields.Float(string="Le reste", readonly=True ,store=True , compute="_reste")

     @api.one

     @api.depends('article_ids', 'article_ids.prix_article')

     ids = odapi.execute_kw(db, uid, password,'bondeversement.article', 'search',

    [[['product_id', '=', 'article_ids.product_id']]])

     [record] = odapi.execute_kw(database, uid, pwd,'bondeversement.article', 'read', [ids])

     nb = 1

     for it in [record]:

          ajout = odapi.execute_kw(database, uid, pwd, 'bondeversement.article', 'write',[[it], [{'article_nb': nb}])

          nb+= 1

     def _calcprix(self):

          total = 0

          for unit in self.article_ids:

               total += unit.prix_article

          self.prix = total

     @api.one

     @api.depends('nutrient_ids', 'nutrient_ids.montant')

     def _reste(self):

          restee = self.prix

      for mealitem in self.nutrient_ids:

           restee -= mealitem.montant

      self.reste = restee

class versements(models.Model):

     _name = 'versement'

     product_id = fields.Integer("PID")

     montant = fields.Float("Versement")

     date = fields.Datetime("Date de versement")

class bondeversement_article(models.Model):

     _name = 'bondeversement.article'

     product_id = fields.Integer("PID")

     article_nb = fields.Integer("Nb")

     namee = fields.Selection(selection =[('bague','Bague'),('boucle','Boucle'),('bracelet','Bracelet'),('ceinture','Ceinture'),('chaine','Chaine'),('ensemble','Ensemble'),('gourmette','Gourmette'),('msayess','Msayess'),('parrure','Parrure'),('pendentif','Pendentif'),('wiz','El-Wiz'),('article_bebe','Article bebe'),('autre','Autre')], string='Article')

     poids_article = fields.Float("Poids")

     prix_article = fields.Float("Prix")