How to add a condition to difflib?

Question

I want to get the closest match for my row from another data frame but with a condition, I currently have it like this:

df['a'].astype(str).apply(lambda x: difflib.get_close_matches(x,df2['a'].astype(str)))

but i want it to get the closest match from df2['a'] when df['b'] == df2['b']. How can i put this in the syntax?