safe progress

shell.nix

@@ -1,5 +1,20 @@
 let
   pkgs = import <nixpkgs> {};
-  python = pkgs.python36;
 in
-  import ./default.nix { inherit pkgs python; }
+pkgs.mkShell {
+  buildInputs = with pkgs; [
+    git
+    nixfmt
+    pkgs.python3
+    pkgs.python3Packages.black
+    pkgs.python3Packages.pytest
+    pkgs.python3Packages.pytest-black
+    pkgs.python3Packages.pytest-flake8
+    pkgs.python3Packages.pytest-mypy
+    pkgs.python3Packages.pytest-pylint
+  ];
+
+  shellHook = ''
+    export PYTHONPATH=${./src}:$PYTHONPATH
+  '';
+}