anchor.diff:        tornado
         colorama
         ]
  +      ++ optionals ( !isPy3k ) [ futures ]
         ++ optionals ( isPy26 ) [ argparse ]
         ++ optionals ( !isPy3k && !isPyPy ) [ websocket_client ]
         ++ optionals ( !isPyPy ) [ numpy pandas greenlet ];
  
positive.code: 
    bokeh = buildPythonPackage rec {
      name = "bokeh-${version}";
      version = "0.12.1";
  
      src = pkgs.fetchurl {
        url = "mirror://pypi/b/bokeh/${name}.tar.gz";
        sha256 = "06d3ed14308f550376d5b0c7e9f2bacb3ff5bbcceefd7f6369d070de71dfa563";
      };
  
      disabled = isPyPy;
  
negative.code:       werkzeug
        itsdangerous
        dateutil
        requests2
        six
        pygments
  