def describe_attachment(attachmentId=None):
    """
    Returns the attachment that has the specified ID. Attachment IDs are generated by the case management system when you add an attachment to a case or case communication. Attachment IDs are returned in the  AttachmentDetails objects that are returned by the  DescribeCommunications operation.
    See also: AWS API Documentation
    
    
    :example: response = client.describe_attachment(
        attachmentId='string'
    )
    
    
    :type attachmentId: string
    :param attachmentId: [REQUIRED]
            The ID of the attachment to return. Attachment IDs are returned by the DescribeCommunications operation.
            

    :rtype: dict
    :return: {
        'attachment': {
            'fileName': 'string',
            'data': b'bytes'
        }
    }
    
    
    """
    pass
