Python shell with override example.

shell.nix

{ pkgs ? import <nixpkgs> {} }: let
  pyversion = version: package: package.overrideAttrs (a: { inherit version; });
in
with pkgs; mkShell {

  buildInputs = [

    (python37.withPackages(a: with a; [

      ipython pylint 
      (pyversion "12.3.0" python-telegram-bot)

    ]))

  ];

}