code: def get_session_indexes(request):
          
          if isinstance(request, etree._Element):
              elem = request
          else:
              if isinstance(request, Document):
                  request = request.toxml()
              elem = fromstring(request, forbid_dtd=True)
  
          session_indexes = []
          session_index_nodes = OneLogin_Saml2_Utils.query(elem, '/samlp:LogoutRequest/samlp:SessionIndex')
          for session_index_node in session_index_nodes:
              session_indexes.append(OneLogin_Saml2_Utils.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