如果给定列的连续nan数达到阈值N，是否找到pandas数据帧中NAN值的第一行和最后一行索引？

import pandas as pd

def find_nan_rows(df, N):
    is_nan = df.isnull()
    nan_count = is_nan.rolling(N).sum()
    start_index = nan_count.shift(-1) == N
    end_index = nan_count == N
    first_row_index = start_index.idxmax()
    last_row_index = end_index.idxmax()
    return first_row_index, last_row_index

# 示例数据帧
df = pd.DataFrame({'A': [1, 2, None, None, None, 6, 7],
                   'B': [None, None, None, 4, 5, None, None],
                   'C': [None, None, None, None, None, None, None]})

# 设置阈值N
N = 3

# 查找连续NaN值的第一行和最后一行索引
first_row_index, last_row_index = find_nan_rows(df, N)

print("第一行索引：", first_row_index)
print("最后一行索引：", last_row_index)

第一行索引： 2
最后一行索引： 4