如何获得彼此嵌入的多个列表的平均值？

def flatten_list(nested_list):
    flattened_list = []
    for sublist in nested_list:
        if isinstance(sublist, list):
            flattened_list.extend(flatten_list(sublist))
        else:
            flattened_list.append(sublist)
    return flattened_list

def calculate_average(nested_list):
    flattened_list = flatten_list(nested_list)
    total_sum = sum(flattened_list)
    length = len(flattened_list)
    average = total_sum / length
    return average

# 示例数据
nested_list = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]
average = calculate_average(nested_list)
print("平均值：", average)