That sounds like one of the "maze of choices" I mentioned, no?

And if you're "writing the whole application in Rust and using Python as a glue language", you don't have the problem that this entire discussion is about, which is when you have Python code that is slow. Python as an extension language is a completely different world. Performance problems there are a much less big deal, because you've already got the option to simply use the fast language with only modestly more complexity, if indeed even that given how nice Rust is once you get used to it. It's when your whole app is in Python that these issues emerge, and "Just write extensions" is an option far less often than portrayed.