anchor.diff:  
     # regenerate python wrapper
     preConfigure = ''
  -    rm hepmc/hepmcwrap.py
       swig -c++ -I${pkgs.hepmc}/include -python hepmc/hepmcwrap.i
     '';
   
  -  buildInputs = [ pkgs.swig pkgs.hepmc ];
  +  nativeBuildInputs = [ pkgs.swig ];
  +  buildInputs = [ pkgs.hepmc ];
   
     HEPMCPATH = pkgs.hepmc;
   
  
positive.code: { stdenv
  , buildPythonPackage
  , fetchPypi
  , isPy3k
  , fetchurl
  , pkgs
  
negative.code:     sha256 = "1210fd7e20d4abc1d9166147a9f7645a2a58b655fe030ad54ab3ea0d0c6e0834";
    };
  
    srcMissing = fetchFromBitbucket {
      owner = "andybuckley";
      repo = "pyhepmc";
      rev = "pyhepmc-1.0.0";
      sha256 = "0vxad143pz45q94w5p0dycpk24insdsv1m5k867y56xy24bi0d4w";
    };
  
    prePatch = ''
      cp -r $srcMissing/hepmc .
      chmod +w hepmc
    '';
  
    patches = [
      # merge PR https://bitbucket.org/andybuckley/pyhepmc/pull-requests/1/add-incoming-outgoing-generators-for/diff
      ./pyhepmc_export_edges.patch
  