Pandas 合并不产生数据

Question

I have 2 dataframes:

df1:

branch    sessions users
toledo    10       3
new york  14       2
boston    102      43
seattle   9        7

df2:

branch    guests
toledo    10      
new york  14       
boston    102      
seattle   9    

The result I'm looking for merges the "guests" column from df2 to df1 like this: df1:

branch    sessions users  guests
toledo    10       3      10
new york  14       2      14
boston    102      43     102
seattle   9        7      9

I've tried concat , join and merge with no luck.

With merge

guest_sessions = df2[['branch','guests']].copy()
pd.merge(df1, guest_sessions, left_index=True, right_index=True)

I get this:

branch_x    sessions    users   guests_x    branch_y    guests_y

What am I doing wrong?