def _delist(series):
    """ turn listed cols into tuples, or extract their single element """
    series = series.copy(deep=True)
    lens = series.dropna().apply(len).unique()
    if len(lens) > 1:
        series[~series.isnull()] = series.dropna().apply(tuple)
    elif len(lens) == 1 and lens.item() == 1:
        series[~series.isnull()] = series.dropna().apply(lambda x: x[0])
    return series
