an ugly method, to constrains odoo default_code (and name)

product.py

# -*- coding: utf-8 -*-
# © 2017 Edi Santoso <[email protected]>
# License LGPL-3.0 or later (https://www.gnu.org/licenses/lgpl.html)
from odoo import api, fields, models, _

class Product(models.Model):
	_inherit = 'product.template'

	@api.constrains('default_code', 'name')
	def _check_code(self):
		if self.default_code or self.name:
			exi = self.env['product.template'].search_count(['|',('name', '=', self.name),('default_code', '=', self.default_code)])
			if exi > 1:
				raise ValueError(_("Code / Name already used !!!"))