anchor.diff:  
     sqlalchemy = pkgs.lib.overrideDerivation sqlalchemy9 (args: rec {
       name = "SQLAlchemy-0.7.10";
  +    disabled = isPy3k;
       src = fetchurl {
         url = "http://pypi.python.org/packages/source/S/SQLAlchemy/${name}.tar.gz";
         sha256 = "0rhxgr85xdhjn467qfs0dkyj8x46zxcv6ad3dfx3w14xbkb3kakp";
  
positive.code:     };
  
      buildInputs = [ pkgs.btrfsProgs ];
      propagatedBuildInputs = with pkgs; [ contextlib2 sqlalchemy8 pyxdg pycparser cffi alembic ];
  
      meta = {
        description = "Deduplication for Btrfs";
  
negative.code: 
    pycurl2 = buildPythonPackage (rec {
      name = "pycurl2-7.20.0";
      disabled = isPy3k;
  
      src = fetchgit {
        url = "https://github.com/Lispython/pycurl.git";
  