anchor.diff:  
     trac = buildPythonPackage {
       name = "trac-0.11.5";
  -    
  +
       src = fetchurl {
         url = http://ftp.edgewall.com/pub/trac/Trac-0.11.5.tar.gz;
         sha256 = "cc3362ecc533abc1755dd78e2d096d1413bc975abc3185318f4821458cd6a8ac";
       };
  -    
  -    doCheck = false;
  -    
  +
  +    doCheck = false;
  +
       PYTHON_EGG_CACHE = "`pwd`/.egg-cache";
  -    
  +
       propagatedBuildInputs = [ genshi pkgs.setuptools ];
  -    
  +
       meta = {
         description = "Enhanced wiki and issue tracking system for software development projects";
  -      
  +
         license = "BSD";
       };
     };
  
positive.code:     name = "psycopg2-2.0.13";
  
      doCheck = false;
      
      src = fetchurl {
        url = "http://initd.org/pub/software/psycopg/PSYCOPG-2-0/${name}.tar.gz";
        sha256 = "0arkaa1nbbd3pyn4l1bc75wi7nff3vxxh4s8sj5al5hv20p64pm1";
      };
      
      propagatedBuildInputs = [ pkgs.postgresql ];
      
      meta = {
        description = "PostgreSQL database adapter for the Python programming language";
        license = "GPLv2/ZPL";
      };
    };
    
    pycryptopp = buildPythonPackage (rec {
      name = "pycryptopp-0.5.15";
  
  
negative.code: 
      buildInputs = [ pkgs.libxml2 pkgs.libxslt ];
  
      meta = {
        description = "Pythonic binding for the libxml2 and libxslt libraries";
        homepage = http://codespeak.net/lxml/index.html;
        license = "BSD";
  