Nix: Python3 include isntalled pacakges site-packages

Author: Brikaa

Diff for: runtimes/python3.nix

@@ -12,7 +12,10 @@ in piston.mkRuntime {
     ];
 
     run = ''
-    PYTHONPATH=$PISTON_PACKAGES_PATH ${pkg}/bin/python3 "$@"
+    FIRST_PATH="''${PISTON_PACKAGES_PATH%%:*}"
+    PYTHON_LIB=$(ls $FIRST_PATH/lib | head -n1)
+    # include /lib/pythonx.x/site-packages after each path
+    PYTHONPATH="''${PISTON_PACKAGES_PATH//://lib/$PYTHON_LIB/site-packages:}/lib/$PYTHON_LIB/site-packages" ${pkg}/bin/python3 "$@"
     '';
 
     packages = pkg.pkgs;