Python: nix-shell with buildEnv is broken

[FRidh]

Executing nix-shell with a shell.nix containing

with import <nixpkgs> {};

( pkgs.python35.buildEnv.override  {
  extraLibs = with pkgs.python35Packages; [ numpy toolz ];
}).env

will give you the interpreter, but not the extra libs numpy and toolz.
@domenkozar

[domenkozar]

It works for me. Note that python is python2.7 from your system, you should invoke python3 -c "import numpy"

[FRidh]

oh my, I must be sleepy still...
Thanks.

[domenkozar]

Happy to help :)

[FRidh]

ok, I really do have an issue here. When I try again it just does not work.

freddy@fr-laptop:/tmp$ cat shell.nix 
with import <nixpkgs> {};

( pkgs.python35.buildEnv.override  {
  extraLibs = with pkgs.python35Packages; [ numpy toolz ];
}).env

freddy@fr-laptop:/tmp$ nix-shell -I nixpkgs=~/Code/nixpkgs --option extra-binary-caches https://hydra.nixos.org --pure --run "python3 -c 'import toolz'"
Traceback (most recent call last):
  File "<string>", line 1, in <module>
ImportError: No module named 'toolz'

freddy@fr-laptop:~/Code/nixpkgs$ git log -1
commit ade9f7167dd1fec622c1f0ff7725cb6f6743b45d
Author: Peter Simons <simons@cryp.to>
Date:   Fri Nov 27 11:16:29 2015 +0100

    nix-prefetch-git: make sure the script is interpreted by bash

    Fixes https://github.com/NixOS/nixpkgs/issues/11284.

[domenkozar]

@FRidh can you pull master and try again?

[FRidh]

It seems that while the nix-shell is active, dependencies, like toolz can be garbage-collected. I don't think that should be possible. I just tested, and that was not possible before.

[FRidh]

Just tested, and indeed it's fixed. They aren't gc-ed anymore either.

[domenkozar]

Yes, packages used with nix-shell are not added to gc root. You have to use something like https://nixos.org/wiki/Development_Environments#Making_a_Persistent_nix-shell_Environment

[FRidh]

What I meant was, when I ran nix-collect-garbage -d while I still had the nix-shell open. Before the fix, dependencies of the environment were gc-ed, while now they aren't.

Anyhow, its works now :)