如何在Dataframe中找到最长的NaNs序列？

import pandas as pd

# 创建一个示例Dataframe
df = pd.DataFrame({'A': [1, 2, None, None, None, 3, 4],
                   'B': [None, None, None, 5, 6, None, None],
                   'C': [7, 8, None, None, None, None, None]})

# 将NaN值转换为布尔值
is_nan = df.isnull()

# 计算每个NaN值之前的非NaN值的累积和
cumsum = is_nan.cumsum()

# 计算每个累积和之间的差异
diff = cumsum.diff()

# 再次计算差异的累积和
cumsum_diff = diff.cumsum()

# 计算每个累积和值的频率
freq = cumsum_diff.value_counts()

# 找到频率最高的值
max_freq = freq.idxmax()

# 找到最长NaN序列的起始和结束位置
start = cumsum_diff[cumsum_diff == max_freq].index[0]
end = cumsum_diff[cumsum_diff == max_freq].index[-1]

# 找到最长NaN序列在原始Dataframe中的位置
longest_nan_sequence = df.loc[start:end]

print(longest_nan_sequence)