Python

You need to get over the bloat of virtual environments. It's the same as node_modules and it's completely necessary if you want more than a single python project to live on your machine.

I personally use poetry as my dependency manager and build tool. It's not perfect but it's a lot better than pipenv or just rawdogging pip like a maniac. uv is the new hotness, but I haven't tried it so can't vouch. People seem to like it though.

JavaScript is also an interpreted language with tons of build tools. The reason to have one for python is mainly about packaging and code distribution, so same as JavaScript. If you want to distribute a program you probably don't want to just point people to a GitHub repo, and if you want to publish a package on pypi it needs to be bundled correctly.

For ecosystem there isn't much I can do for you, it completely depends on what you'll be working on. Baseline you want pydantic for parsing objects, assuming some APIs will be involved. You want black for code formatting, flake8 for linting, pytest for testing. If you're gonna write your own APIs you can't go wrong with fastapi, which works great with pydantic. For nice console stuff there's click for building cli apps and rich and textual for console output and live console apps respectively.

People are actively trying to replace flake8 and black with feature compatible stuff written in rust but again I haven't tried those so can't vouch.

Coming from react you're gonna need to pretty quickly switch gears to thinking more object oriented. You're gonna be annoyed at how you can't just quickly declare a deeply nested interface, that's just how it is. The biggest change other than object oriented thinking will probably be decorators. Typescript had them experimentally and only for classes, python has them for classes and functions natively. They're a bit tricky to wrap your mind around when you want to write your own, but not too bad. A lot of Google hits will be outdated on this front. Google specifically "decorators ParamSpec" to see how to make them properly.

Good luck in your new job, you'll be grand!