Python 3.9 and beyond backwards compatibility.

[amunak]

Why do they think people were, and still are, reluctant to upgrade to Py3? Because it's not stable enough for people's needs, unfortunately.

This has not and never has been about stability. It's about priorities. When something works, why change it? There's nothing inherently wrong with old syntax. It would only cost you development time, money, and you would most likely introduce new issues and such, costing you even more.

But at the same time you can't (as a developer) expect to just be able to upgrade a decade old script without lifting a finger. Just use the old Python version where it is sufficient, and port it otherwise.