def fetch_tmp_weights_fnames(resu_dir, simu_id, fold_idx) : 
    """ Get temporary weights filenames

    Parameters
    ----------
    resu_dir: filename
        Path of the directory in which to save the results.
    simu_id: string
        Name of the simulation, to be used to name files.
    fold_idx : int 
        Index of the current fold

    Return
    ------
    tmp_weights_fnames : list of list of strings
        [subsample_idx][task_idx] = tmp filename

    """
    fname = "%s/%s.fold_%d.tmp_weights_fnames" % (resu_dir, simu_id, fold_idx)
    with open (fname, 'r' ) as f : 
        tmp_weights_fnames = [line.split() for line in f.readlines()]
    return tmp_weights_fnames