I created a field of type Boolean 'check_barcode' in the stock.config.settings object. The intent of this field is as follows if it is marked as true it would have entered a method that is in another inherited object. The problem is that my self.env is not bringing the check_barcode field (I think it's not making the stay). 

field.py

class StockSettings(models.TransientModel):

    _inherit = 'stock.config.settings'

    check_barcode = fields.Boolean(string='check_barcode')

product.py

class ProductTemplate(models.Model):

    _inherit = "product.template"

    @api.onchange('barcode')

    def calculate_checksum(self):

            #if self.env.user.company_id.product_ids.compute(self.company_id.check_barcode, self.product_ids):

            #if self.env['res.config.settings'].check_barcode:                                    #.company_id.product_ids.compute(self.company_id.check_barcode, self.product_ids):

        if self.check_barcode == 'True':

            if self.barcode:

                barcode = self.barcode[:12]

                if len(barcode) < 12:

                    barcode = barcode.ljust(12, '0')

                sum_ = lambda x, y: int(x) + int(y)

                evensum = reduce(sum_, barcode[::2])

                oddsum = reduce(sum_, barcode[1::2])

                digit = (10 - ((evensum + oddsum * 3) % 10)) % 10

                self.write(

                    {

                        'barcode': barcode + str(digit)

                    }

            )

            else:

                return False