buildPythonPackage not found

with import <nixpkgs> {};
let
ansicolor = buildPythonPackage rec {
    name = "ansicolor-${version}";
    version = "0.2.4";

    src = pkgs.fetchurl{
      url = "mirror://pypi/a/ansicolor/${name}.tar.gz";
      sha256 = "0zlkk9706xn5yshwzdn8xsfkim8iv44zsl6qjwg2f4gn62rqky1h";
    };

    meta = {
      homepage = "https://github.com/numerodix/ansicolor/";
      description = "A library to produce ansi color output and colored highlighting and diffing";
    };
}; in
stdenv.mkDerivation rec {
  name = "env";
  env = buildEnv { name = name; paths = buildInputs; };
  buildInputs = [
    python ansicolor pythonPackages.jupyter
  ];
}

#command line output
error: undefined variable ‘buildPythonPackage’ at /tmp/x/default.nix:3:13
(use ‘--show-trace’ to show detailed location information)

#with --show-trace
Error: while evaluating the attribute ‘env’ of the derivation ‘env’ at /tmp/x/default.nix:20:3:
while evaluating the attribute ‘pkgs’ of the derivation ‘env’ at /nix/store/vhakj9wg0cbj8pz2ckk4wd7x80xp28dw-nixos-17.09pre106916.c5badb123a/nixos/pkgs/build-support/trivial-builders.nix:7:14:
undefined variable ‘buildPythonPackage’ at /tmp/x/default.nix:3:13