What is the `(...).env` attribute?

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1

Just found out that that via the 15.19.1.2.1. Python library packages in Nixpkgs chapter in the Nixpkgs manual that the results of the following shell.nix scripts when called with nix-shell are the same:

  • using mkShell:

    { pkgs ? import <nixpkgs> {} }:

let
  pythonEnv =
    pkgs.python38.withPackages (
      packages:
        [ packages.django
          packages.psycopg2
        ]
    );
in
  pkgs.mkShell {
    buildInputs = [
      pythonEnv
    ];
  }

  • using (...).env

    { pkgs ? import <nixpkgs> {} }:

(
    pkgs.python38.withPackages (
      packages:
      [ packages.django
        packages.psycopg2
      ]
    )
).env

What is the env attribute? Is it a general one or specific to the result of Pyhon packages?

2

In this case, it’s a byproduct of using withPackages (and, more specifically, because withPackages in turn uses buildEnv. It isn’t quite general, but (without confirming) I would guess that the other language ecosystems that have withPackages/buildEnv functions have the same attribute.

I’m not sure if there’s a lengthier description somewhere, but I found a reference to this a few sections later:

15.19.2.2.6. python.withPackages function

…
As python.withPackages simply uses python.buildEnv under the hood, it also supports the env attribute. The shell.nix file from the previous section can thus be also written like this:

1 Like
3

Thanks! I didn’t read below the 15.19.2. Reference section which was obviously a mistake…