    def __init__(self, txid=None, output=None):
        """Create an instance of a :class:`~.TransactionLink`.

            Note:
                In an IPLD implementation, this class is not necessary anymore,
                as an IPLD link can simply point to an object, as well as an
                objects properties. So instead of having a (de)serializable
                class, we can have a simple IPLD link of the form:
                `/<tx_id>/transaction/outputs/<output>/`.

            Args:
                txid (str, optional): A Transaction to link to.
                output (int, optional): An Outputs's index in a Transaction with
                    id `txid`.
        """
        self.txid = txid
        self.output = output
Create an instance of a :class:`~.TransactionLink`.

Note:
In an IPLD implementation, this class is not necessary anymore,
as an IPLD link can simply point to an object, as well as an
objects properties. So instead of having a (de)serializable
class, we can have a simple IPLD link of the form:
`/<tx_id>/transaction/outputs/<output>/`.

Args:
txid (str, optional): A Transaction to link to.
output (int, optional): An Outputs's index in a Transaction with
id `txid`.
bigchaindb/common/transaction.py