anchor.diff:  
     zope_exceptions = buildPythonPackage rec {
        name = "zope.exceptions-${version}";
  -     version = "4.0.5";
  +     version = "4.0.8";
   
        src = pkgs.fetchurl {
          url = "http://pypi.python.org/packages/source/z/zope.exceptions/${name}.tar.gz";
  -       md5 = "c95569fcb444ae541777de7ae5297492";
  +       sha256 = "0zwxaaa66sqxg5k7zcrvs0fbg9ym1njnxnr28dfmchzhwjvwnfzl";
        };
   
        propagatedBuildInputs = with self; [ zope_interface ];
  +
  +     # circular deps
  +     doCheck = false;
   
        meta = {
          description = "Exception interfaces and implementations";
  
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_interface = buildPythonPackage rec {
      name = "zope.interface-4.1.3";
  
      src = pkgs.fetchurl {
        url = "http://pypi.python.org/packages/source/z/zope.interface/${name}.tar.gz";
        sha256 = "0ks8h73b2g4bkad821qbv0wzjppdrwys33i7ka45ik3wxjg1l8if";
      };
  
      propagatedBuildInputs = with self; [ zope_event ];
  