Form Preview
​

# -*- coding: utf-8 -*-
from odoo import models, fields, api, _

class StockInherit(models.Model):
_inherit="stock.production.lot"

mfg_date = fields.Date('Mfg Date')
Purity = fields.Float('Purity %')

i want to add field in that form which is show in Preview 
but this form is open when user click on create and Edit from line 
there is no id which i can inherit i also active developer mode but can't show id