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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def fulfill_transaction(transaction, *, private_keys):
 """Fulfills the given transaction. Args: transaction (dict):
 The transaction to be fulfilled. private_keys (:obj:`str` | :obj:`list` | :obj:`tuple`):
 One or more private keys to be used for fulfilling the transaction. Returns: dict: The fulfilled transaction payload, ready to be sent to a BigchainDB federation. Raises: :exc:`~.exceptions.MissingPrivateKeyError`: If a private key is missing. """

    if not isinstance(private_keys, (list, tuple)):
        private_keys = [private_keys]

    # NOTE: Needed for the time being. See
    # https://github.com/bigchaindb/bigchaindb/issues/797
    if isinstance(private_keys, tuple):
        private_keys = list(private_keys)

    transaction_obj = Transaction.from_dict(transaction)
    try:
        signed_transaction = transaction_obj.sign(private_keys)
    except KeypairMismatchException as exc:
        raise MissingPrivateKeyError('A private key is missing!') from exc

    return signed_transaction.to_dict()