~ ⌚ 14:36:37
$ nix-build python.nix -I nixpkgs=channel:nixos-17.09
these derivations will be built:
  /nix/store/wcq6dxz18f0xna54mrrkcx2dzf4awb0d-test-py.drv
building '/nix/store/wcq6dxz18f0xna54mrrkcx2dzf4awb0d-test-py.drv'...
156
/nix/store/066fqdvgfnzdr27i1ffz7cghf8r89glg-stdenv/setup: line 1013: /nix/store/y4vvxb579rb8wy5jhsq9znb08jz2skj8-test-py/pythonpath: No such file or directory
builder for '/nix/store/wcq6dxz18f0xna54mrrkcx2dzf4awb0d-test-py.drv' failed with exit code 1
error: build of '/nix/store/wcq6dxz18f0xna54mrrkcx2dzf4awb0d-test-py.drv' failed

~ ⌚ 14:36:44
$ nix-build python.nix -I nixpkgs=channel:nixos-17.03
these derivations will be built:
  /nix/store/n7ivqa9p879isa50l8fxal63xj15zyq4-test-py.drv
building '/nix/store/n7ivqa9p879isa50l8fxal63xj15zyq4-test-py.drv'...
88
/nix/store/p4avr9pw3sa68ivryc490fvqmnws0zyv-stdenv/setup: line 854: /nix/store/7a8kr8nzb8sm51a6hirldxpb61740irq-test-py/pythonpath: No such file or directory
builder for '/nix/store/n7ivqa9p879isa50l8fxal63xj15zyq4-test-py.drv' failed with exit code 1
error: build of '/nix/store/n7ivqa9p879isa50l8fxal63xj15zyq4-test-py.drv' failed

~ ⌚ 14:36:47
$ cat python.nix
let
  pkgs = (import <nixpkgs> {});
in
  pkgs.stdenv.mkDerivation {
    name = "test-py";
    buildInputs = [
      pkgs.pythonFull
      pkgs.pythonPackages.pandas
      pkgs.pythonPackages.scikitlearn
      pkgs.pythonPackages.matplotlib
      pkgs.pythonPackages.plotly
      pkgs.pythonPackages.statsmodels
    ];
    buildCommand = ''
      echo $PYTHONPATH | awk -F\: '{print NF}'
      echo $PYTHONPATH > $out/pythonpath
    '';
  }