old_contents: # -*- coding: utf-8 -*-
  # Part of Odoo. See LICENSE file for full copyright and licensing details.
  
  from odoo import api, fields, models
  from odoo.addons.purchase.models.purchase import PurchaseOrder as Purchase
  
  
  class PurchaseOrder(models.Model):
      _inherit = "purchase.order"
  
      l10n_in_journal_id = fields.Many2one('account.journal', string="Journal", \
          states=Purchase.READONLY_STATES, domain="[('type', '=', 'purchase')]")
      l10n_in_gst_treatment = fields.Selection([
              ('regular', 'Registered Business - Regular'),
              ('composition', 'Registered Business - Composition'),
              ('unregistered', 'Unregistered Business'),
              ('consumer', 'Consumer'),
              ('overseas', 'Overseas'),
              ('special_economic_zone', 'Special Economic Zone'),
              ('deemed_export', 'Deemed Export')
          ], string="GST Treatment", states=Purchase.READONLY_STATES)
      l10n_in_company_country_code = fields.Char(related='company_id.country_id.code', string="Country code")
  
      @api.onchange('company_id')
      def l10n_in_onchange_company_id(self):
          if self.l10n_in_company_country_code == 'IN':
              domain = [('company_id', '=', self.company_id.id), ('type', '=', 'purchase')]
              journal = self.env['account.journal'].search(domain, limit=1)
              if journal:
                  self.l10n_in_journal_id = journal.id
  
      @api.onchange('partner_id', 'company_id')
      def onchange_partner_id(self):
          if self.l10n_in_company_country_code == 'IN':
              self.l10n_in_gst_treatment = self.partner_id.l10n_in_gst_treatment
              self.onchange_l10n_in_gst_treatment()
          return super().onchange_partner_id()
  
new_contents: # -*- coding: utf-8 -*-
  # Part of Odoo. See LICENSE file for full copyright and licensing details.
  
  from odoo import api, fields, models
  from odoo.addons.purchase.models.purchase import PurchaseOrder as Purchase
  
  
  class PurchaseOrder(models.Model):
      _inherit = "purchase.order"
  
      l10n_in_journal_id = fields.Many2one('account.journal', string="Journal", \
          states=Purchase.READONLY_STATES, domain="[('type', '=', 'purchase')]")
      l10n_in_gst_treatment = fields.Selection([
              ('regular', 'Registered Business - Regular'),
              ('composition', 'Registered Business - Composition'),
              ('unregistered', 'Unregistered Business'),
              ('consumer', 'Consumer'),
              ('overseas', 'Overseas'),
              ('special_economic_zone', 'Special Economic Zone'),
              ('deemed_export', 'Deemed Export')
          ], string="GST Treatment", states=Purchase.READONLY_STATES)
      l10n_in_company_country_code = fields.Char(related='company_id.country_id.code', string="Country code")
  
      @api.onchange('company_id')
      def l10n_in_onchange_company_id(self):
          if self.l10n_in_company_country_code == 'IN':
              domain = [('company_id', '=', self.company_id.id), ('type', '=', 'purchase')]
              journal = self.env['account.journal'].search(domain, limit=1)
              if journal:
                  self.l10n_in_journal_id = journal.id
  
      @api.onchange('partner_id', 'company_id')
      def onchange_partner_id(self):
          if self.l10n_in_company_country_code == 'IN':
              self.l10n_in_gst_treatment = self.partner_id.l10n_in_gst_treatment
          return super().onchange_partner_id()
  
subject: remove undefined method call