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)