eiru_datepay_accountinvoice/models/account_invoice_date.py

# -*- coding: utf-8 -*-
from openerp import api, fields, models
from openerp.exceptions import except_orm
from datetime import datetime, timedelta
from openerp.tools import DEFAULT_SERVER_DATE_FORMAT
from dateutil.relativedelta import relativedelta


class AccountInvoice(models.Model):
    _inherit = 'account.invoice'

    date_pay = fields.Date("Fecha de Posible Pago")