anchor.diff:    });
   
     virtualenv = buildPythonPackage rec {
  -    name = "virtualenv-1.10";
  +    name = "virtualenv-1.11.4";
       src = fetchurl {
         url = "http://pypi.python.org/packages/source/v/virtualenv/${name}.tar.gz";
  -      md5 = "9745c28256c70c76d36adb3767a00212";
  +      md5 = "9accc2d3f0ec1da479ce2c3d1fdff06e";
       };
   
       inherit recursivePthLoader;
  
positive.code: 
    virtualenv-clone = buildPythonPackage rec {
      name = "virtualenv-clone-0.2.4";
      
      src = fetchgit {
        url = "https://github.com/berdario/virtualenv-clone.git";
        rev = ''c302ca84e524cb22f88c834cccb23dd410cced97'';
      };
  
      doCheck = false;
  
      meta = with stdenv.lib; {
  
negative.code: 
  
    py = buildPythonPackage rec {
      name = "py-1.4.20";
  
      src = fetchurl {
        url = "https://pypi.python.org/packages/source/p/py/${name}.tar.gz";
        md5 = "5f1708be5482f3ff6711dfd6cafd45e0";
      };
    };
  
  