Instruct the server to add the given items to the specified
        Item List (which will be created if it does not already exist)

        :type item_urls: List or ItemGroup
        :param item_urls: List of URLs for the items to add,
            or an ItemGroup object
        :type item_list_name: String
        :param item_list_name: name of the item list to retrieve

        :rtype: String
        :returns: the server success message, if successful

        :raises: APIError if the request was not successful

def add_to_item_list_by_name(self, item_urls, item_list_name):
        """ Instruct the server to add the given items to the specified
        Item List (which will be created if it does not already exist)

        :type item_urls: List or ItemGroup
        :param item_urls: List of URLs for the items to add,
            or an ItemGroup object
        :type item_list_name: String
        :param item_list_name: name of the item list to retrieve

        :rtype: String
        :returns: the server success message, if successful

        :raises: APIError if the request was not successful


        """
        url_name = urlencode((('name', item_list_name),))
        request_url = '/item_lists?' + url_name

        data = json.dumps({'items': list(item_urls)})
        resp = self.api_request(request_url,  method='POST', data=data)
        return self.__check_success(resp)