wrapPythonProgram: exclude Python itself from PYTHONPATH

pkgs/development/python-modules/generic/wrap.sh

@@ -17,6 +17,8 @@ buildPythonPath() {
     declare -A pythonPathsSeen=()
     program_PYTHONPATH=
     program_PATH=
+    pythonPathsSeen["@python@"]=1
+    addToSearchPath program_PATH @python@/bin
     for path in $pythonPath; do
         _addToPythonPath $path
     done

pkgs/top-level/python-packages.nix

@@ -42,6 +42,7 @@ in modules // {
     { deps = pkgs.makeWrapper;
       substitutions.libPrefix = python.libPrefix;
       substitutions.executable = python.interpreter;
+      substitutions.python = python;
       substitutions.magicalSedExpression = let
         # Looks weird? Of course, it's between single quoted shell strings.
         # NOTE: Order DOES matter here, so single character quotes need to be