<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def __get_untitled_file_name(self):
 """ Returns an untitled file name. :return: Untitled file name. :rtype: unicode """


        untitledNameId = Editor._Editor__untitled_name_id
        for file in self.list_files():
            if not os.path.dirname(file) == self.__default_session_directory:
                continue

            search = re.search(r"\d+", os.path.basename(file))
            if not search:
                continue

            untitledNameId = max(int(search.group(0)), untitledNameId) + 1

        name = "{0} {1}.{2}".format(self.__default_file_name, untitledNameId, self.__default_file_extension)
        Editor._Editor__untitled_name_id += 1
        LOGGER.debug("> Next untitled file name: '{0}'.".format(name))
        return name