def add_transaction(self, transaction):

        transaction_template = ('\n{date} {t.payee}\n'

                                '{postings}')

        posting_template = ('  {account} {p.amount.symbol}'

                            ' {p.amount.amount}\n')

        output  = b''

        output += transaction_template.format(

            date=transaction.date.strftime('%Y-%m-%d'),

            t=transaction,

            postings=''.join([posting_template.format(

                p=p,

                account=p.account + ' ' * (

                    80 - (len(p.account) + len(p.amount.symbol) +

                    len(p.amount.amount) + 1 + 2)

                )) for p in transaction.postings])).encode('utf8')

        with open(self.ledger_file, 'ab') as f:

            f.write(output)

        _log.debug('written to file: %s', output)