python: provide better message if python interpreter is not supported

pkgs/development/python-modules/generic/default.nix

@@ -49,10 +49,9 @@
 
 , ... } @ attrs:
 
-assert (!disabled);
 
 # Keep extra attributes from `attrs`, e.g., `patchPhase', etc.
-python.stdenv.mkDerivation (attrs // {
+if disabled then throw "${name} not supported for interpreter ${python.executable}" else python.stdenv.mkDerivation (attrs // {
   inherit doCheck;
 
   name = namePrefix + name;