'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
:type dry_run: bool
:param dry_run: Set to True if the operation should not actually run.
:rtype: list of :class:`boto.ec2.snapshotattribute.SnapshotAttribute`
:return: The requested Snapshot attribute'

def get_snapshot_attribute(self, snapshot_id, attribute='createVolumePermission', dry_run=False):

    params = {'Attribute': attribute}
    if snapshot_id:
        params['SnapshotId'] = snapshot_id
    if dry_run:
        params['DryRun'] = 'true'
    return self.get_object('DescribeSnapshotAttribute', params, SnapshotAttribute, verb='POST')
