let pkgs = import (fetchTarball "https://github.com/NixOS/nixpkgs/archive/b62d2a95c72fb068aecd374a7262b37ed92df82b.tar.gz") {}; in pkgs.mkShell { packages = [ (pkgs.python313.withPackages (python-pkgs: with python-pkgs; [ # select Python packages here flask flask-sqlalchemy psycopg2 ])) ]; }