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: 
  
    zope_proxy = buildPythonPackage rec {
      name = "zope.proxy-4.1.4";
  
      src = pkgs.fetchurl {
        url = "http://pypi.python.org/packages/source/z/zope.proxy/${name}.tar.gz";
        md5 = "3bcaf8b8512a99649ecf2f158c11d05b";
      };
  
      propagatedBuildInputs = with self; [ zope_interface ];
  
      meta = {
          maintainers = with maintainers; [ goibhniu ];
  
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";
  