How to COALESCE in Pandas

This function returns the first non-null value between 2 columns.

import pandas as pd
import numpy as np


df=pd.DataFrame({"A":[1,2,np.nan,4,np.nan],"B":['A',"B","C","D","E"]})

df

     A  B
0  1.0  A
1  2.0  B
2  NaN  C
3  4.0  D
4  NaN  E

In the following example, it will return the values of column A and if they are null, it will return the corresponding value of column B.

df['A'].combine_first(df['B'])

0    1.0
1    2.0
2      C
3    4.0
4      E