code: def default_node(self, value):
          
  
          if value is not None:
              assert issubclass(value, AbstractCompositeNode), \
                  "'{0}' attribute: '{1}' is not a '{2}' subclass!".format(
                      "default_node", value, AbstractCompositeNode.__name__)
          self.__default_node = value
docs: Setter for **self.__default_node** attribute.
  
          :param value: Attribute value.
          :type value: AbstractCompositeNode or GraphModelNode