anchor.diff:      };
     };
   
  -  zc_recipe_egg_fun = { buildout, version, md5 }: buildPythonPackage rec {
  +  zc_recipe_egg_fun = { buildout, version, sha256 }: buildPythonPackage rec {
       inherit version;
       name = "zc.recipe.egg-${version}";
   
  
positive.code: 
      src = pkgs.fetchurl {
        url    = "https://pypi.python.org/packages/source/T/Twiggy/Twiggy-0.4.5.tar.gz";
        # md5 = "b0dfbbb7f56342e448af4d22a47a339c"; # provided by pypi website.
        sha256 = "4e8f1894e5aee522db6cb245ccbfde3c5d1aa08d31330c7e3af783b0e66eec23";
      };
  
  
negative.code: 
      src = pkgs.fetchurl {
        url = https://pypi.python.org/packages/source/p/python3-pika/python3-pika-0.9.14.tar.gz;
        sha256 = "1c3hifwvn04kvlja88iawf0awyz726jynwnpcb6gn7376b4nfch7";
      };
      buildInputs = with self; [ nose mock pyyaml ];
  
  