anchor.diff:  
     smmap = buildPythonPackage rec {
       name = "smmap-0.8.2";
  +    disabled = isPy3k;  # next release will have py3k support
       meta.maintainers = [ stdenv.lib.maintainers.mornfall ];
   
       src = fetchurl {
  
positive.code: 
    http_signature = buildPythonPackage (rec {
      name = "http_signature-0.1.4";
  
      src = fetchurl {
        url = "http://pypi.python.org/packages/source/h/http_signature/${name}.tar.gz";
  
negative.code: 
    muttils = buildPythonPackage (rec {
      name = "muttils-1.3";
      disabled = isPy3k;
  
      src = fetchurl {
        url = http://www.blacktrash.org/hg/muttils/archive/8bb26094df06.tar.bz2;
  