anchor.diff:  
       src = pkgs.fetchurl {
         url = "http://pypi.python.org/packages/source/p/pbkdf2/${name}.tar.gz";
  -      md5 = "40cda566f61420490206597243dd869f";
  +      sha256 = "ac6397369f128212c43064a2b4878038dab78dab41875364554aaf2a684e6979";
       };
   
       # ImportError: No module named test
  
positive.code: 
      src = pkgs.fetchurl {
        url = "https://pypi.python.org/packages/source/W/Wand/${name}.tar.gz";
        md5 = "10bab03bf86ce8da2a95a3b15197ae2e";
      };
  
      buildInputs = with self; [ pkgs.imagemagick pytest psutil memory_profiler pytest_xdist ];
  
negative.code: 
      src = pkgs.fetchurl {
        url = "http://pypi.python.org/packages/source/s/sh/${name}.tar.gz";
        sha256 = "590fb9b84abf8b1f560df92d73d87965f1e85c6b8330f8a5f6b336b36f0559a4";
      };
  
      doCheck = false;
  