anchor.diff:  
       src = pkgs.fetchurl {
         url = "http://pypi.python.org/packages/source/i/importlib/importlib-1.0.2.tar.gz";
  -      md5 = "4aa23397da8bd7c7426864e88e4db7e1";
  +      sha256 = "131jvp6ahllcqblszjg6fxrzh4k50w8g60sq924b4nb8lxm9dl14";
       };
     };
   
  
positive.code: 
      src = pkgs.fetchurl {
        url = "http://pypi.python.org/packages/source/d/django-classy-tags/${name}.tar.gz";
        md5 = "eb686aa767ad8cf88c1fa0f400a42516";
        sha256 = "0wxvpmjdzk0aajk33y4himn3wqjx7k0aqlka9j8ay3yfav78bdq0";
      };
  
  
negative.code:     doCheck = false;
  
      src = pkgs.fetchurl {
        inherit sha256;
        url = "https://pypi.python.org/packages/source/z/zc.recipe.egg/zc.recipe.egg-${version}.tar.gz";
      };
      meta.broken = true;  # https://bitbucket.org/pypa/setuptools/issues/462/pkg_resourcesfind_on_path-thinks-the
  