Expanding the rows of a data frame based on its column containing lists

Question

My original data -

pd.DataFrame([
        {'col1': 1, 'col2': 11, 'col3': ['A', 'B'] },
        {'col1': 2, 'col2': 22, 'col3': ['P', 'Q', 'R'] },
    ])

which gives me -

   col1  col2          col3
0     1    11          ['A', 'B']
1     2    22     ['P', 'Q', 'R']

I'd like to expand the rows depending on contents of the array in col3 i.e. I'd like to get a dataframe like this one -

    col1  col2 col3
0     1    11   'A'
1     1    11   'B'
2     2    22   'P'
3     2    22   'Q'
4     2    22   'R'

What's a good way accomplishing this? I found a similar question here however it doesn't include col3 in the output.

I also have another similar question here however since it has strings in the column. The same solution wouldn't work here because split() wouldn't work for list.