from odoo import models,fields

# car/models/car.py

class Car(models.Model):

   _name = 'car.car'

   name  = fields.Char('Car name', size=25)

   brand = fields.Char('Car brand',default='Citroën DS',size=25)

   country = fields.Char('Country name ',default='France',size=30)

   def __init__(self):

        return 'The car name is : %s,\nIts brand is : %s,\nIts manufactured country is : %s.\n' %    (self.name,self.brand,self.country)

# car/models/product_template.py   

class ProductTemplate(models.Model):

   _inherits = 'product.template'

   _name     = 'product.template'

   car       = fields.Many2one('car.car', string='Car name', ondelete='SET NULL', auto_join=True)

My error is : Before to fill the car informations, in Sales/Products/Products, into tab 'General Information' i selected 'Storable Product' value in 'Product Type' field. Right now i am filling the car informations, 'save' successfully. I wanna edit the value of 'Product Type', from 'Storable Product' to 'Consumable' or 'Service', i got 

this error :

File "/odoo/odoo12/odoo/models.py", line 5384, in onchange

for cmd in values[name]:

TypeError: 'int' object is not iterable"

Please helps.