anchor.diff:  assert enableQt -> pyqt5 != null;
   
   buildPythonPackage rec {
  -  version = "3.3.4";
  +  version = "3.4.1";
     pname = "matplotlib";
   
     disabled = !isPy3k;
   
     src = fetchPypi {
       inherit pname version;
  -    sha256 = "3e477db76c22929e4c6876c44f88d790aacdf3c3f8f3a90cb1975c0bf37825b0";
  +    sha256 = "84d4c4f650f356678a5d658a43ca21a41fca13f9b8b00169c0b76e6a6a948908";
     };
   
     XDG_RUNTIME_DIR = "/tmp";
  
positive.code: { lib, stdenv, fetchPypi, writeText, python, buildPythonPackage, isPy3k, pycairo, backports_functools_lru_cache
  , which, cycler, dateutil, nose, numpy, pyparsing, sphinx, tornado, kiwisolver
  , freetype, libpng, pkg-config, mock, pytz, pygobject3, gobject-introspection
  , certifi, pillow
  , enableGhostscript ? true, ghostscript ? null, gtk3
  , enableGtk3 ? false, cairo
  
negative.code:     ++ lib.optional stdenv.isDarwin [ Cocoa ];
  
    propagatedBuildInputs =
      [ cycler dateutil numpy pyparsing tornado freetype qhull
        kiwisolver certifi libpng mock pytz pillow ]
      ++ lib.optionals enableGtk3 [ cairo pycairo gtk3 gobject-introspection pygobject3 ]
      ++ lib.optionals enableTk [ tcl tk tkinter libX11 ]
      ++ lib.optionals enableQt [ pyqt5 ];
  