anchor.diff:  { stdenv
   , buildPythonPackage
   , fetchPypi
  +, fetchpatch
   , isPy3k
   , setuptoolsDarcs
   , darcsver
  
positive.code:   buildInputs = [ setuptoolsDarcs darcsver pkgs.cryptopp ];
  
    meta = with stdenv.lib; {
      homepage = http://allmydata.org/trac/pycryptopp;
      description = "Python wrappers for the Crypto++ library";
      license = licenses.gpl2Plus;
      platforms = platforms.linux;
  
negative.code: 
    src = fetchPypi {
      inherit pname version;
      sha256 = "17v98bhh3nd6rkw0kk1xmnc9vm5ql0fji4in2wyd4zlvlfhmgb88";
    };
  
    patches = [
      (fetchpatch {
        name = "pycryptopp-cryptopp_6.patch";
        url = "https://aur.archlinux.org/cgit/aur.git/plain/api_change.patch?h=pycryptopp&id=55f2973d6ca5e9e70438f2eadb7fb575b1a5048d";
        sha256 = "0lvl2d32d2vkb0v6d39p9whda5bdrmlsjd41zy0x0znqm53a9i99";
        stripLen = 1;
        extraPrefix = "src/";
      })
    ];
  
    # Prefer crypto++ library from the Nix store over the one that's included
    # in the pycryptopp distribution.
  