flake.nix

{
  description = "A Nix-flake-based Python development environment";

  # GitHub URLs for the Nix inputs we're using
  inputs = {
    # Simply the greatest package repository on the planet
    nixpkgs.url = "github:NixOS/nixpkgs";
    # A set of helper functions for using flakes
    flake-utils.url = "github:numtide/flake-utils";
    mach-nix.url = "github:DavHau/mach-nix";
  };

  outputs = { self, nixpkgs, flake-utils, mach-nix }:
    flake-utils.lib.eachDefaultSystem (system:
      let
        pkgs = import nixpkgs { inherit system; };

        python = pkgs.python39;

        pythonEnv = mach-nix.lib.${system}.mkPython {
          requirements = builtins.readFile ./requirements.txt;
        };

        pythonTools = with pkgs.python39Packages; [ pip virtualenv ];
      in {
        devShells = {
          default = pkgs.mkShell {
            # Packages included in the environment
            buildInputs = [ pythonEnv ] ++ pythonTools;

            # Run when the shell is started up
            shellHook = ''
              ${python}/bin/python --version
            '';
          };
        };

        packages = { venv = pythonEnv; };

        defaultPackage = mach-nix.lib.${system}.mkPythonShell {
          requirements = builtins.readFile ./requirements.txt;
        };
      });
}