'Adds one or more attachments to an attachment set. If an
`AttachmentSetId` is not specified, a new attachment set is
created, and the ID of the set is returned in the response. If
an `AttachmentSetId` is specified, the attachments are added
to the specified set, if it exists.
An attachment set is a temporary container for attachments
that are to be added to a case or case communication. The set
is available for one hour after it is created; the
`ExpiryTime` returned in the response indicates when the set
expires. The maximum number of attachments in a set is 3, and
the maximum size of any attachment in the set is 5 MB.
:type attachment_set_id: string
:param attachment_set_id: The ID of the attachment set. If an
`AttachmentSetId` is not specified, a new attachment set is
created, and the ID of the set is returned in the response. If an
`AttachmentSetId` is specified, the attachments are added to the
specified set, if it exists.
:type attachments: list
:param attachments: One or more attachments to add to the set. The
limit is 3 attachments per set, and the size limit is 5 MB per
attachment.'

def add_attachments_to_set(self, attachments, attachment_set_id=None):

    params = {'attachments': attachments}
    if (attachment_set_id is not None):
        params['attachmentSetId'] = attachment_set_id
    return self.make_request(action='AddAttachmentsToSet', body=json.dumps(params))
