flake.nix

{
  inputs.nixpkgs.url = "github:NixOS/nixpkgs/nixos-21.11";
  inputs.flake-utils.url = "github:numtide/flake-utils";

  outputs = { self, nixpkgs, flake-utils }:
  flake-utils.lib.eachDefaultSystem (system:
  let
    pkgs = nixpkgs.legacyPackages.${system};
    py = pkgs.python39.withPackages (ps: with ps; [
      click flask jinja2 ldap
    ]);
  in {
    devShell = pkgs.mkShell {
      buildInputs = [
        py
      ];
      shellHook = ''
          # Tells pip to put packages into $PIP_PREFIX instead of the usual locations.
          # See https://pip.pypa.io/en/stable/user_guide/#environment-variables.
          export PIP_PREFIX=$(pwd)/_build/pip_packages
          export PYTHONPATH="$PIP_PREFIX/${pkgs.python39.sitePackages}:$(pwd):$PYTHONPATH"
          export PATH="$PIP_PREFIX/bin:$PATH"
          unset SOURCE_DATE_EPOCH
      '';
    };
  });
}