如何迭代Pandas数据帧，并应用阈值函数删除x%为null的列？

import pandas as pd

data = {'A': [1, 2, None, 4, 5],
        'B': [None, 2, 3, 4, 5],
        'C': [1, 2, 3, 4, 5]}
df = pd.DataFrame(data)

threshold = 0.5  # 阈值为50%
for column in df.columns:
    if df[column].isnull().mean() > threshold:
        df.drop(column, axis=1, inplace=True)

print(df)

import pandas as pd

data = {'A': [1, 2, None, 4, 5],
        'B': [None, 2, 3, 4, 5],
        'C': [1, 2, 3, 4, 5]}
df = pd.DataFrame(data)

threshold = 0.5  # 阈值为50%
for column in df.columns:
    if df[column].isnull().mean() > threshold:
        df.drop(column, axis=1, inplace=True)

print(df)