anchor.diff:      ++ stdenv.lib.optional enableGtk2 pygtk
       ++ stdenv.lib.optionals enableGtk3 [ cairo pycairo gtk3 gobject-introspection pygobject3 ]
       ++ stdenv.lib.optionals enableTk [ tcl tk tkinter libX11 ]
  -    ++ stdenv.lib.optionals enableQt [ pyqt4 ];
  +    ++ stdenv.lib.optionals enableQt [ pyqt5 ];
   
     patches =
       [ ./basedirlist.patch ];
  
positive.code: , enableGtk3 ? false, cairo
  # darwin has its own "MacOSX" backend
  , enableTk ? !stdenv.isDarwin, tcl ? null, tk ? null, tkinter ? null, libX11 ? null
  , enableQt ? false, pyqt4
  , libcxx
  , Cocoa
  , pythonOlder
  
negative.code:                 && (tkinter != null)
                  && (libX11 != null)
                  ;
  assert enableQt -> pyqt5 != null;
  
  buildPythonPackage rec {
    version = "3.1.1";
  