Is it possible in Python to construct a one-liner RETURN statement with a main IF condition which is a "gateway" for other conditions to check?

I'll try to make it clearer with an example code:

def is_opposite(string_1, string_2):
    if string_1.lower() == string_2.lower():
        if len(string_1) == # some value:
            return # do smth
        elif len(string_2) == # some value:
            return # do smth
    return # do smth

There's a main if string_1.lower() == string_2.lower(): condition that prevents a nested block of code to run when False. So how can that code be written in a single return ... line? If can.

Thank you.