pandas过滤某列含有nan 的行

pandas中 过滤某列中含有Nan的行

import pandas as pd
import numpy as np

 """
 过滤某列中含有Nan的行
 :return:
 """
 df = pd.DataFrame({'A': [1, 2, 3, 4], 'B': [5, 6, 7, None]})
 # method1
 df_filter = df.drop(df[np.isnan(df['B'])].index)
 # method2
 df_filter2 = df.dropna(subset=['B'])