anchor.diff:  
   
     zope_interface = buildPythonPackage rec {
  -    name = "zope.interface-4.1.1";
  +    name = "zope.interface-4.1.3";
   
       src = pkgs.fetchurl {
         url = "http://pypi.python.org/packages/source/z/zope.interface/${name}.tar.gz";
  -      md5 = "edcd5f719c5eb2e18894c4d06e29b6c6";
  +      sha256 = "0ks8h73b2g4bkad821qbv0wzjppdrwys33i7ka45ik3wxjg1l8if";
       };
   
       propagatedBuildInputs = with self; [ zope_event ];
  
positive.code: 
      propagatedBuildInputs = with self; [ zope_interface zope_exceptions zope_testing six ] ++ optional (!python.is_py3k or false) subunit;
  
      # https://github.com/zopefoundation/zope.testrunner/issues/35
      doCheck = !(isPy27 || isPy34);
  
      meta = {
        description = "A flexible test runner with layer support";
        homepage = http://pypi.python.org/pypi/zope.testrunner;
        license = licenses.zpt20;
        maintainers = with maintainers; [ goibhniu ];
      };
  
      # Python 3.5 is not yet supported.
      disabled = isPy35;
    };
  
  
  
negative.code: 
    zope_exceptions = buildPythonPackage rec {
       name = "zope.exceptions-${version}";
       version = "4.0.8";
  
       src = pkgs.fetchurl {
         url = "http://pypi.python.org/packages/source/z/zope.exceptions/${name}.tar.gz";
         sha256 = "0zwxaaa66sqxg5k7zcrvs0fbg9ym1njnxnr28dfmchzhwjvwnfzl";
       };
  
       propagatedBuildInputs = with self; [ zope_interface ];
  
       # circular deps
       doCheck = false;
  
       meta = {
         description = "Exception interfaces and implementations";
  