Called during initialization. Only needs to be explicitly
        called if save_and_close_attributes is explicitly called
        beforehand.

def open_attributes_file(self):
        '''
        Called during initialization. Only needs to be explicitly
        called if save_and_close_attributes is explicitly called
        beforehand.
        '''
        if not self.saveable():
            raise AttributeError("Cannot open attribute file without a valid file")
        if self._db_closed:
            self._fd = FileDict(self._file_name, db_ext=self._db_ext,
                                   read_only=self._read_only, clear=False, cache_size=0,
                                   immutable_vals=False, stringify_keys=False,
                                   cache_misses=False)
            self._db_closed = False