You don't need to actually convert anything: Python 2's str can be identified with Python 3's bytes, and unicode with str. You 'just' need to have their __geta

You don't need to actually convert anything: Python 2's str can be identified with Python 3's bytes, and unicode with str. You 'just' need to have their __getattribute__ methods, along with a ton of standard library functions, check the Python version of the caller and change behavior accordingly. Ugly, but I think it would mostly 'just work' for user code.