I'm trying to install this Python library python3.6-geopandas-0.3.0. And I successfully installed it imperatively with

$ nix-env -iA nixpkgs.python3Packages.geopandas

However I need to create an expression so that my Python environment includes it.

with import <nixpkgs> {};

python36.withPackages (ps: with ps; [

Turns out I get

installing ‘python3-3.6.4-env’
error: undefined variable ‘geopandas’

I have both nixos and nixpkgs-unstable configured in my system. Not sure if correctly though. I have channel nixos for root and nixpkgs for my user.

$ echo $NIX_PATH 

I would like to make nixpkgs-unstable the default channel for my user, or at least make its packages visible as an overlay, so I could run the above expression successfully.

closed as unclear what you're asking by Wildcard, G-Man, X Tian, Archemar, Rui F Ribeiro Feb 17 '18 at 17:09

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Your expression works for me on current nixpkgs master. I would investigate if your NIX_PATH isn't taking some old <nixpkgs> that you didn't expect, e.g. geopandas isn't present on the 17.09 stable branch.

  • $ echo $NIX_PATH nixpkgs=/nix/var/nix/profiles/per-user/root/channels/nixos/nixpkgs:nixos-config=/etc/nixos/configuration.nix:/nix/var/nix/profiles/per-user/root/channels – dmvianna Feb 16 '18 at 11:08
  • I would like to use stable in root and unstable in the user environment. Is that possible? – dmvianna Feb 18 '18 at 9:32

I was able to reproduce this on NixOS.

Your NIX_PATH sets nixpkgs to /nix/var/nix/profiles/per-user/root/channels/nixos/nixpkgs which if you look up is just a symlink to /nix/var/nix/profiles/per-user/root/channels/nixos/. It's probably a little hack to make work all the expressions that are in the wild that expect <nixpkgs> to point to a valid channel path (even though I don't think it's a requirement for a nix system and seems to originate from nix-daemon).

To fix it you either have to redefine NIX_PATH to point to an actual nixpkgs channel or you have to explicitly state the path to the channel instead of using <nixpkgs> in your expression.

You can find your available channels in ~/.nix-defexpr:

$tree -l -L 2 ~/.nix-defexpr/
├── channels -> /nix/var/nix/profiles/per-user/user1/channels
│   ├── ...
│   └── nixpkgs -> /nix/store/qz1.../nixpkgs
└── channels_root -> /nix/var/nix/profiles/per-user/root/channels
    ├── ...
    └── nixos -> /nix/store/53b.../nixos

(channels contains the user-specific channels while channels_root contains the channels that root subscribed to and are available to all users)

So if you decided to use the user1's subscription to nixpkgs then you would run:

NIX_PATH="nixpkgs=/home/user1/.nix-defexpr/channels/nixpkgs" nix-env -f default.nix -i

  • I understood everything until the last line. However what I need to do is to set nixpkgs-unstable as the default channel for my user. I will not be using a default.nix file. How would I correct the behaviour then? – dmvianna Feb 17 '18 at 20:32
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    <nixpkgs> is not some magic bound to a "default channel" - it just instructs nix to look into the NIX_PATH linux environment variable and look for an assignment of the form "nixpkgs=..." and use the right side of the assignment as the value of <nixpkgs>. You can prefix any command in linux with an assignment like I showed above and it will set the environment variable just for that one command invocation. – fghibellini Feb 17 '18 at 20:39
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    I believe the config gets passed the package set of the 'nixos' channel root is subscribed to, but I cannot find any documentation regarding it. – fghibellini Feb 23 '18 at 21:22
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    another example of using fixed channels with a good explanation garbas.si/2015/reproducible-development-environments.html – fghibellini Feb 25 '18 at 13:57

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