如何根据python中的指定条件将一行的值复制到另一行？

Question

我的数据框架如下：

df_a = pd.DataFrame({'Month':['Jan','Feb','Mar','Apr','May','Jun','Jul','Aug','Sep','Oct','Nov','Dec',
                            'Jan','Feb','Mar','Apr','May','Jun','Jul','Aug','Sep','Oct','Nov','Dec'],
                    'Year':[2018,2018,2018,2018,2018,2018,2018,2018,2018,2018,2018,2018,
                            2019,2019,2019,2019,2019,2019,2019,2019,2019,2019,2019,2019],
                    'Nutri':["Yes","Yes","Yes","Yes","Yes","Yes","No","No","No","No","No","No",
                                "No","No","No","No","No","No","No","No","No","No","No","No"]})

条件是，如果Nutri列在一年中的任何月份显示为“是”，则我希望在该列中填写该年的所有“是”，如下所示：

df_a = pd.DataFrame({'Month':['Jan','Feb','Mar','Apr','May','Jun','Jul','Aug','Sep','Oct','Nov','Dec',
                            'Jan','Feb','Mar','Apr','May','Jun','Jul','Aug','Sep','Oct','Nov','Dec'],
                    'Year':[2018,2018,2018,2018,2018,2018,2018,2018,2018,2018,2018,2018,
                            2019,2019,2019,2019,2019,2019,2019,2019,2019,2019,2019,2019],
                    'Nutri':["Yes","Yes","Yes","Yes","Yes","Yes","Yes","Yes","Yes","Yes","Yes","Yes",
                                "No","No","No","No","No","No","No","No","No","No","No","No"]})

我试图用下面的逻辑提出if条件，但它不起作用：

if df_a[(df_a['Year'] == 2018 ) & (df_a['Nutri'] == 'Yes')]:
    df_a['Nutri'] == 'Yes'
print(df_a)    

我迷路了，下一步该怎么办。请帮忙