Get information about an attribute of a snapshot.  Only one attribute
        can be specified per call.

        :type snapshot_id: str
        :param snapshot_id: The ID of the snapshot.

        :type attribute: str
        :param attribute: The requested attribute.  Valid values are:

                          * createVolumePermission

        :rtype: list of :class:`boto.ec2.snapshotattribute.SnapshotAttribute`
        :return: The requested Snapshot attribute

def get_snapshot_attribute(self, snapshot_id,
                               attribute='createVolumePermission'):
        """
        Get information about an attribute of a snapshot.  Only one attribute
        can be specified per call.

        :type snapshot_id: str
        :param snapshot_id: The ID of the snapshot.

        :type attribute: str
        :param attribute: The requested attribute.  Valid values are:

                          * createVolumePermission

        :rtype: list of :class:`boto.ec2.snapshotattribute.SnapshotAttribute`
        :return: The requested Snapshot attribute
        """
        params = {'Attribute' : attribute}
        if snapshot_id:
            params['SnapshotId'] = snapshot_id
        return self.get_object('DescribeSnapshotAttribute', params,
                               SnapshotAttribute, verb='POST')