code: def get_session_indexes(request):
          
  
          elem = OneLogin_Saml2_XML.to_etree(request)
          session_indexes = []
          session_index_nodes = OneLogin_Saml2_XML.query(elem, '/samlp:LogoutRequest/samlp:SessionIndex')
          for session_index_node in session_index_nodes:
              session_indexes.append(OneLogin_Saml2_XML.element_text(session_index_node))
          return session_indexes
docs: Gets the SessionIndexes from the Logout Request
          :param request: Logout Request Message
          :type request: string|DOMDocument
          :return: The SessionIndex value
          :rtype: list