eiru_invoice_status_change/model/eiru_invoice_status_change.py

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

from openerp import api, fields, models

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

    @api.model
    def update_invoice_state(self, ids):
        updateInvoice = None
        invoiceState = None

        accountInvoice = self.env['account.invoice'].browse(ids)

        if (not accountInvoice):
            return

        if (accountInvoice.residual > 0 and accountInvoice.state == 'paid'):
            invoiceState = 'open'

        if (accountInvoice.residual <= 0 and accountInvoice.state == 'open'):
            invoiceState = 'paid'

        if (invoiceState):
            updateInvoice = accountInvoice.write({'state': invoiceState})

        return True if (updateInvoice) else False