How to update column value based on another value in pandas

I have the below data frame

| A | B|
|Jan|10|
|Feb|20|
|Mar|30|
|Apr|20|

Required Output – I want to check for March from A and get its corresponding value from B and add that value to remaining B values to update the dataframe using pandas

| A |B |
|Jan|40|
|Feb|50|
|Apr|50|

>Solution :

You can do it in one line, pandas-style, using set_index():

df = df.set_index('A').pipe(lambda x: x.assign(B=x['B'] + x.loc['Mar', 'B'])).drop('Mar').reset_index()

Output:

>>> df
     A   B
0  Jan  40
1  Feb  50
2  Apr  50

Or in multiple lines (not so pandas-style):

df['B'] += df.loc[df['A'] == 'Mar', 'B'].iloc[0]
df = df[df['A'] != 'Mar']

Or a third and slightly shorter way:

tmp = df.set_index('A').T
df = (tmp.pop('Mar').iloc[0] + tmp.T['B']).reset_index()