    def to_dict(self):
        """Transforms the object to a Python dictionary.

            Returns:
                (dict|None): The link as an alternative serialization format.
        """
        if self.txid is None and self.output is None:
            return None
        else:
            return {
                'transaction_id': self.txid,
                'output_index': self.output,
            }
Transforms the object to a Python dictionary.

Returns:
(dict|None): The link as an alternative serialization format.
bigchaindb/common/transaction.py