anchor.diff:  
   
     py = buildPythonPackage rec {
  -    name = "py-1.4.20";
  +    name = "py-1.4.24";
   
       src = fetchurl {
         url = "https://pypi.python.org/packages/source/p/py/${name}.tar.gz";
  -      md5 = "5f1708be5482f3ff6711dfd6cafd45e0";
  +      md5 = "8f32ee0cd1e01472a255fe1d28d81217";
       };
     };
   
  
positive.code:         pythonPackages.selenium;
  
      meta = with stdenv.lib; {
        maintainers = with maintainers; [ iElectric lovek323 ];
        platforms = platforms.unix;
      };
    };
  
negative.code:   };
  
    pytest = buildPythonPackage rec {
      name = "pytest-2.6.2";
  
      src = fetchurl {
        url = "http://pypi.python.org/packages/source/p/pytest/${name}.tar.gz";
        md5 = "0a1735fb1d481ef3864f34678607ba85";
      };
  
      preCheck = ''
        # don't test bash builtins
        rm testing/test_argcomplete.py
      '';
  
      propagatedBuildInputs = [ py ]
  