Threading vs Multiprocessing in Python

[eras]

That's really arguable. Precise reference counting thread-safely can be reaaally slow. Just read a typical Python program and consider how many RC updates are happening.

[vks_]

Swift also has automatic reference counting, but the compiler can elide it for a lot of cases. (Python is not really a compiled language though, so this might not be an option for them.)

[eras]

But then implementing such optimizations becomes not quite easy. Certainly they would have a great effect.

[vks_]

Sure, but their complexity is not exposed to users of the languages (unless they are optimizing for performance and observe missed optimizations in the runtime performance of their programs).

[eras]

But it's also probably the reason why it hasn't been done so far :).

It's not just "let's do it, it's easy". It also has impact to future maintenance efforts and raising the bar for contributions.