python删除大多数列都是nans的行

import pandas as pd
import numpy as np

data = {'A': [1, np.nan, np.nan, 4],
        'B': [np.nan, 2, np.nan, 5],
        'C': [np.nan, np.nan, np.nan, np.nan],
        'D': [6, 7, 8, 9]}
df = pd.DataFrame(data)

threshold = 0.8  # 定义NaN值的阈值，大于该阈值的行将被删除
df.dropna(thresh=threshold*df.shape[1], inplace=True)

print(df)