'copy incoterm from purchase order to invoice'

def _prepare_invoice(self):

    invoice = super(PurchaseOrder, self)._prepare_invoice()
    if self.incoterm_id:
        invoice['incoterm_id'] = self.incoterm_id.id
    if self.partner_id.country_id:
        invoice['intrastat_country_id'] = self.partner_id.country_id.id
    return invoice
