Rust did it with its "edition" system, where you can freely mix and match modules from the 2015 edition with modules from the 2018 edition. Unfortunately, in th

Rust did it with its "edition" system, where you can freely mix and match modules from the 2015 edition with modules from the 2018 edition. Unfortunately, in the Python 2 to Python 3 transition a fundamental data type (strings) changed, which would make freely mixing Python 2 and Python 3 code much harder.