遍历dataframe中的单元格并搜索缺少的值

import pandas as pd
import numpy as np

df = pd.DataFrame({'A': [1, 2, np.nan, 4],
                   'B': [5, np.nan, 7, 8],
                   'C': [9, 10, 11, np.nan]})

missing_values = []
for column in df.columns:
    for index, value in df[column].iteritems():
        if pd.isnull(value):
            missing_values.append((index, column))

for index, column in missing_values:
    print(f"Missing value at index {index} in column {column}")