factura_venta_bioelectric/models/account_invoice.py

# -*- coding: utf-8 -*-

from openerp import api, models, fields

class account_invoice(models.Model):
    _inherit = "account.invoice"
    _name = 'account.invoice'

    pedido_por = fields.Char(string='Pedido por')
    ficha_nro = fields.Char(string='Ficha Nº')