Fill blank cells from previous columns pandas python

Question

If I have a simple dataframe such as:

q_1     q_1_mark    q_2    q_2_mark
TRUE    a           1      c
FALSE   b           2   
TRUE    c           3   
<         


        

Answer 1

df.q_2_mark.fillna(df.q_1_mark, inplace=True)

df
     q_1 q_1_mark  q_2 q_2_mark
0   True        a    1        c
1  False        b    2        b
2   True        c    3        c

Answer 2

Assuming your dataframe is df, Try:

df.q_2_mark = df.q_2_mark.combine_first(df.q_1_mark) 

     q_1 q_1_mark  q_2 q_2_mark
0   True        a    1        c
1  False        b    2        b
2   True        c    3        c