How can I add a nix package when using buildPythonPackage? - nix

Question

The Python Part
I have a python application with multiple entrypoints, json_out and json_in. I can run them both with this default.nix
with import <nixpkgs> {};
(
let jsonio = python37.pkgs.buildPythonPackage rec {
pname = "jsonio";
version = "0.0.1";
src = ./.;
};
in python37.withPackages (ps: [ jsonio ])
).env
Like so:
$ nix-shell --run "json_out"
{ "a" : 1, "b", 2 }
$ nix-shell --run "echo { \"a\" : 1, \"b\", 2 } | json_in"
keys: a,b
values: 1,2
The System Part
I want to also invoke jq in the nix shell, like this:
$ nix-shell --run --pure "json_out | jq '.a' | json_in"
But I can't because it is not included. I know that I can include jq into the nix shell using this default.nix
with import <nixpkgs> {};
stdenv.mkDerivation rec {
name = "jsonio-environment";
buildInputs = [ pkgs.jq ];
}
And it works on its own:
$ nix-shell --run --pure "echo { \"a\" : 1, \"b\", 2 } | jq '.a'"
{ "a" : 1 }
But now I don't have my application:
$ nix-shell --run "json_out | jq '.a'"
/tmp/nix-shell-20108-0/rc: line 1: json_out: command not found
The Question
What default.nix file can I provide that will include both my application and the jq package?

Answer 1

My preferred way to achieve this is to use .overrideAttrs to add additional dependencies to the environment like so:
with import <nixpkgs> {};
(
let jsonio = python37.pkgs.buildPythonPackage rec {
pname = "jsonio";
version = "0.0.1";
src = ./.;
};
in python37.withPackages (ps: [jsonio ])
).env.overrideAttrs (drv: {
buildInputs = [ jq ];
})

Answer 2

I needed to:
provide the output of buildPythonPackage as part of the input of mkDerivation
omit the env. Based on a hint from an error message:
Python 'env' attributes are intended for interactive nix-shell
sessions, not for building!
Here's what I ended up with:
with import <nixpkgs> {};
let jsonio_installed = (
let jsonio_module = (
python37.pkgs.buildPythonPackage rec {
pname = "jsonio";
version = "0.0.1";
src = ./.;
}
);
in python37.withPackages (ps: [jsonio_module ])
);
in stdenv.mkDerivation rec {
name = "jsonio-environment";
buildInputs = [ pkgs.jq jsonio_installed ];
}