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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _save(self):
 """ save the cache index, in case it was modified. Saves the index table and the file name repository in the file `index.dat` """


        if self.__modified_flag:
            self.__filename_rep.update_id_counter()
            indexfilename = os.path.join(self.__dir, "index.dat")
            self._write_file(
                indexfilename,
                (self.__index,
                 self.__filename_rep))

            self.__modified_flag = False