old_contents: # -*- coding: utf-8 -*-
  from openerp import api, fields, models
  
  
  class Product(models.Model):
      _inherit = 'stock.pack.operation'
  
      provider_ref = fields.Char(string="Provider Reference",
                                 compute="_compute_product_code")
  
      @api.multi
      @api.depends('provider_ref')
      def _compute_product_code(self):
          for line in self:
              product_supplier = self.env['product.supplierinfo'].search(
                  [('product_tmpl_id', '=', self.product_id.product_tmpl_id.id)])
              if product_supplier:
                  line.provider_ref = product_supplier[0].product_code
  
new_contents: # -*- coding: utf-8 -*-
  from openerp import api, fields, models
  
  
  class Product(models.Model):
      _inherit = 'stock.pack.operation'
  
      provider_ref = fields.Char(string="Provider Reference",
                                 compute="_compute_product_code")
  
      @api.multi
      @api.depends('provider_ref')
      def _compute_product_code(self):
          for line in self:
              product_supplier = self.env['product.supplierinfo'].search(
                  [('product_tmpl_id', '=', line.product_id.product_tmpl_id.id)])
              if product_supplier:
                  line.provider_ref = product_supplier[0].product_code
  
subject: Fix review