code: def __ConstructRelativePath(self, method_config, request,
                                  relative_path=None):
          
          python_param_names = util.MapParamNames(
              method_config.path_params, type(request))
          params = dict([(param, getattr(request, param, None))
                         for param in python_param_names])
          params = util.MapRequestParams(params, type(request))
          return util.ExpandRelativePath(method_config, params,
                                         relative_path=relative_path)
docs: Determine the relative path for request.