[jacquesm]

It's not really Python that was sped up though, it was an application written in python augmented with a bit of optimized rust code.

This sort of hybrid is super common, you typically spend 90%+ of your time in computationally intensive problems in a very small subset of your code, typically the innermost loops. Optimizing those will have very good pay-off.

Traditionally we'd do this with high level stuff in one language and then assembly for the performance critical parts, these days it is more likely a combination of a scripting language for the high level part and a compiled language for the low level parts (C, rust, whatever). Java and such as less suitable for such optimization purposes, both because they come with a huge runtime and because they are hard to interface to other languages unless they happen to use the same underlying VM, but then there usually isn't much performance gain.

Another nice way to optimize computationally intensive code is by finding out if the code is suitable for adaptation to the GPU, which can give you many orders of magnitude speed improvement in some cases.