def METHOD_NAME(df: pd.DataFrame) -> str:
    """
    Get a not existing column name in a DataFrame
    :param df: The DataFrame where to get a not existing column
    :return: The name of a not existing column, e.g. temp_col_0 or temp_col_1
    """
    i = 0
    col = 'temp_col_'
    while True:
        if col + str(i) in df.columns:
            i += 1
        else:
            break
    return col + str(i)