anchor.diff:  
     thumborPexif = self.buildPythonPackage rec {
       name = "thumbor-pexif-0.14";
  +    disabled = ! isPy27;
   
       src = pkgs.fetchurl {
         url = "https://pypi.python.org/packages/source/t/thumbor-pexif/${name}.tar.gz";
  
positive.code: 
    weboob = buildPythonPackage rec {
      name = "weboob-1.0";
  
      src = pkgs.fetchurl {
        url = "https://symlink.me/attachments/download/289/${name}.tar.gz";
  
negative.code:     };
    };
  
  }; in pythonPackages
  