Hi am new to both python and Odoo development, I used the web interface for customization before. I was trying to create a class to 

1. add a field to sale.subscription Model

subscription_tier = fields.Char(string='Subscription Tier',readonly=True)

enter code here

2. loop through subscription line to see if the customer has silver or gold subscription then set it to the field subscription_tier
3. 


class subscription_tire_set(models.Model):
    _inherit = 'sale.subscription'

    subscription_tier = fields.Char(string='Subscription Tier',readonly=True)

    @api.depends('recurring_invoice_line_ids.product_id')
    def _compute_release_to_pay(self):
        for n_subscription in self:
            result = None
            for n_subscription_line in n_subscription.recurring_invoice_line_ids:
                if any(n_subscription_line.product_id) == 'gold':

                    result = gold'
                    break
                else:
                    result = 'not'

        subscription_tier = result

I probably am doing something horribly wrong 

also a getting this massge when trying to open any customer in subscription

Something went wrong! sale.subscription(10,).subscription_tier

Thank u for the help in advance.