@moritzschaefer please fix the merge conflict.

Thanks for your response!

As discussed here (#89213), I refrain now from adding python packages this way. I think NUR is a better destination for it. Sorry for not having colsed this

As it was extremely difficult for me to install swifter, here is how I did it:
flake.nix

{
    description = "Your desc here";
    inputs = {
        nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
    };
    outputs = inputs:
        let 
            nixpkgs = inputs.nixpkgs;
            system = "x86_64-linux";
            pkgs = (import nixpkgs { inherit system; }).pkgs;
        in {
            devShell."${system}" = pkgs.mkShell {
                buildInputs = with pkgs; [ python3Full clangStdenv ];
                shellHook = ''
                  source ./.venv/bin/activate
                  export LD_LIBRARY_PATH=${nixpkgs.lib.makeLibraryPath [pkgs.stdenv.cc.cc]}
                '';
            };
        };
}

requirements.txt

#other packages
swifter

then the first time, do:

python -m venv .venv
source .venv/bin/activate
pip install -r requirements.txt

This took me two days as I tried the following things:

• using the method cited above without this line in the shellHook:

export LD_LIBRARY_PATH=${nixpkgs.lib.makeLibraryPath [pkgs.stdenv.cc.cc]}

this resulted in this error:

Traceback (most recent call last):
  ...
    import pandas._libs.window.aggregations as window_aggregations
ImportError: libstdc++.so.6: cannot open shared object file: No such file or directory

• then I tried using mach-nix but it has a problem specifically with swifter that causes this error:

collision between `/nix/store/zn4ksalrynlx3iwd4d0ldq7aiqn84ysv-python3.8-opencensus-context-0.1.2/lib/python3.8/site-packages/opencensus/common/__pycache__/__init__.cpython-38.pyc' and `/nix/store/2cfyjnic605mjr5j7zck88gk7bkqwpim-python3.8-opencensus-0.7.12/lib/python3.8/site-packages/opencensus/common/__pycache__/__init__.cpython-38.pyc'

I opened an issue about it.

• then I tried to build swifter using the things I found on this PR and in this file from the same person
  I however didn't succeed in making a correct overlay for python so that work went down the drain too.
• finally I came back to my first idea and user the tips that was mentionned in this NixOS Discourse question.

I'm writing this as it might be of use to a future poor soul that wants to install this package.
I lost much more time that this package will never save me but I learned along the way so that's fine ;)
It would be of great use however if this type of info was a bit easier to find in the first place as this is more than frustrating.