def sign(self, tx=None, wifs=[]):
if tx:<EOL><INDENT>txbuffer = self.transactionbuilder_class(tx, blockchain_instance=self)<EOL><DEDENT>else:<EOL><INDENT>txbuffer = self.txbuffer<EOL><DEDENT>txbuffer.appendWif(wifs)<EOL>txbuffer.appendMissingSignatures()<EOL>txbuffer.sign()<EOL>return txbuffer.json()<EOL>
Sign a provided transaction witht he provided key(s)

            :param dict tx: The transaction to be signed and returned
            :param string wifs: One or many wif keys to use for signing
                a transaction. If not present, the keys will be loaded
                from the wallet as defined in "missing_signatures" key
                of the transactions.