如何将多个现有数据框值​更改为nan

import pandas as pd
import numpy as np

df1 = pd.DataFrame({'A': [1, 2, 3], 'B': [4, 5, 6]})
df2 = pd.DataFrame({'A': [7, 8, 9], 'B': [10, 11, 12]})

df1.replace([1, 4], np.nan, inplace=True)
df2.replace(9, np.nan, inplace=True)

print(df1)
print(df2)

     A    B
0  NaN  NaN
1  2.0  5.0
2  3.0  6.0

     A     B
0  7.0  10.0
1  8.0  11.0
2  NaN  12.0