求助一个 pandas 问题，使用布尔筛选 DataFrame 后，怎么对某一列赋值生效

[jiang123574]

[zhusimaji]

import pandas as pd

import numpy as np
dates=pd.date_range('20130201',periods=6)

a=pd.DataFrame(np.arange(24).reshape((6,4)),index=dates,columns=['a','b','c','d'])
print(a)
a.loc[a['a']==12,'b']=5
print(a)
---------------------------------------------------------------------
a b c d
2013-02-01 0 1 2 3
2013-02-02 4 5 6 7
2013-02-03 8 9 10 11
2013-02-04 12 13 14 15
2013-02-05 16 17 18 19
2013-02-06 20 21 22 23
a b c d
2013-02-01 0 1 2 3
2013-02-02 4 5 6 7
2013-02-03 8 9 10 11
2013-02-04 12 5 14 15
2013-02-05 16 17 18 19
2013-02-06 20 21 22 23

[jiang123574]

@zhusimaji 感谢大佬