NixOS notes

Overriding a Python package version using a Nixpkgs overlay

Python 3.12 requires a newer version of Babel than is packaged in the NixOS 23.11 channel. It can be overridden using the following overlay.

let
  fixBabel = (self: super: {
    python312 = super.python312.override {
      packageOverrides = python-self: python-super: {
        babel = python-super.babel.overridePythonAttrs (oldAttrs: rec {
          version = "2.14.0";
          src = super.fetchPypi {
            pname = "Babel";
            inherit version;
            hash = "sha256-aRmGfbA2OYuiHrXHoPayirjLw656c6ROvjSudKTn02M=";
          };
        });
      };
    };
  });

which can then be applied to nixpkgs using

pkgs = nixpkgs.legacyPackages.${system}.extend fixBabel;

or similar.

Missing pyproject.toml when using poetry2nix

Poetry2nix by default removes all files in .gitignore from the source directory when building a Python package. Check whether *.toml or similar is in your .gitignore; this might be the case if you use TOML for files you don't want to commit, e.g. config files.