def __setitem__(self, key, value):
        """Stand-in for dict[key] = value.

        :type key: object
        :param key: Hashable dictionary key.

        :type value: object
        :param value: Dictionary value.

        :raises: :class:`KeyError` always since the future is intended to fail
                 as a dictionary.
        """
        raise KeyError((key, value) % 'Cannot set %r -> %r on a future')
dataset/ETHPy150Open GoogleCloudPlatform/gcloud-python/gcloud/storage/batch.py/_FutureDict.__setitem__/swapped operands of `%`