Thank you :) I learnt a lot from your commit! :)

I'm using stable and just had this as an override which is why I had to pin aiohttp, and copy that config over from the latest unstable to get it to build on my machine.

Trying to upgrade just aiohttp package from unstable and get it working with this code warped my mind a little bit and I wasn't able to figure it out.

@Alan01252 ok, I see. I suggest that we drop the aiohttp pinning then as this will probably quickly become too difficult to maintain as the stable and unstable branches diverge further (in the worst case we would have to pin every dependency). It would be nice to have but generally I try to avoid all overrides that are not necessary (I'd actually like to avoid the psutil and jsonschema overrides as well, but in the past I often had bad luck (bugs) when ignoring the version constraints from upstream). But at the same time I agree that this could be useful to have.

As for your use-case: If you use channels you could try something like this in your NixOS configuration (untested but looks fine - source):

{ config, pkgs, ... }:
let
  unstable = import <nixos-unstable> {};
in {
  environment.systemPackages = [ unstable.packagehere ];
}

Or if you use a local git checkout the following should work:

{ config, pkgs, ... }:
let
  unstable = import /path/to/nixpkgs {};
in {
  environment.systemPackages = [ unstable.packagehere ]; # Or maybe unstable.pkgs.packagehere
}

Maybe also interesting (but most likely without the allowUnfree = true; example): https://nixos.wiki/wiki/Cheatsheet#Customizing_Packages

With nix-shell and nix-env this is possible as well (I can also post an example if you want).

Hope this helps.

No this is great thank you. The problem I was having is I wanted "stable" python but "unstable" aiohttp and that combination I just could not figure out. I should probably just move to unstable python.
I should also mention to get ubridge to work proplerly with gns3 ( using local server ) I had to make sure that all the executables were started in the same directory so I've got this.

`
security.wrappers.gns3 = {
source = "${pkgs.myGns3.guiStable.out}/bin/gns3";
owner = "nobody";
group = "nogroup";
};

security.wrappers.gns3server = {
source = "${pkgs.myGns3.serverStable.out}/bin/gns3server";
owner = "nobody";
group = "nogroup";
};

security.wrappers.ubridge = {
source = "${pkgs.ubridge.out}/bin/ubridge";
owner = "nobody";
group = "nogroup";
capabilities = "cap_net_admin,cap_net_raw+ep";
};

In my configuration to make this work