Merge two python pandas data frames of different length + sum common values

Question

I have the following problem: I have two pandas data frames of different length containing some rows that have common values and some that are different like this:

df1

Answer 1

Solution

df1.add(df2, fill_value=0)

or

df1.add(df2, fill_value=0).astype(int)

This does exactly what you want using arguments intended to solve this exact problem. I added astype(int) at the end to preserve int