Last time I tried (maybe 2 months ago on NixOS 22.05), I found several different tools that claimed to be able to do this and they all failed in various ways; some failed quickly, others took a long time to fail. I ended up using my brain as an SAT solver and manually copying in nix expressions from older versions of nixpkgs that matched versions of the python libs that were needed.
The Python ecosystem also doesn't seem to have a sensible solution for dependency declaration in general. It's kind of remarkable that anything works at all in Python land, it's a lot of "let's hope it works often enough". To be fair it does work out a lot of the time, but when that fails you end up coming to people like me.
I should do some research and see if I can figure out the best way to do this in Python, but I don't use Python at all personally or professionally.
* Pip-tools(requirements.in + requirements.txt)
* Poetry (pyproject.toml+poetry.lock)
* Pipenv(Pipfile+Pipfile.lock)
Those and others enable easy declaration of direct dependencies and compile (resolve) a lock file of the actual dependency graph with hashes. Those tools have their issues and idiosyncrasies, but the dependency declaration aspect seems sensible and functional.
Now that pip supports pinning with a sha (I say “now that”, this was added years ago but it wasn’t always thus), it seems it should be trivial to map onto the Nix model.
I have been working with poetry and playing with poetry2nix so haven’t tried raw pip requirements files with Nix.
I've had some success with Poetry. But then I ran into programs that invoke pip during startup...