def _save(self):
if self.__modified_flag:<EOL><INDENT>self.__filename_rep.update_id_counter()<EOL>indexfilename = os.path.join(self.__dir, "<STR_LIT>")<EOL>self._write_file(<EOL>indexfilename,<EOL>(self.__index,<EOL>self.__filename_rep))<EOL>self.__modified_flag = False<EOL><DEDENT>
save the cache index, in case it was modified.

Saves the index table and the file name repository in the file
`index.dat`