anchor.diff:  
       src = pkgs.fetchurl {
         url = "https://pypi.python.org/packages/source/b/bugwarrior/${name}.tar.gz";
  -      # md5 = "09c93f86a27ffc092e69b46889a3bf50"; # provided by pypi website.
         sha256 = "efe41756c152789f39006f157add9bedfa2b85d2cac15c067e635e37c70cb8f8";
       };
   
  
positive.code: 
      src = pkgs.fetchurl {
        url = "http://pypi.python.org/packages/source/d/django-reversion/${name}.tar.gz";
        md5 = "2de5a3fe82aaf505c134570f96fcc7a8";
        sha256 = "0z8fxvxgbxfnalr5br74rsw6g42nry2q656rx7rsgmicd8n42v2r";
      };
  
  
negative.code: 
      src = pkgs.fetchurl {
        url = "http://pypi.python.org/packages/source/d/django-classy-tags/${name}.tar.gz";
        sha256 = "0wxvpmjdzk0aajk33y4himn3wqjx7k0aqlka9j8ay3yfav78bdq0";
      };
  
  