anchor.diff:  
     buildInputs = [ flex bison zlib proj gdal libtiff libpng fftw sqlite pkgconfig cairo
     readline ffmpeg makeWrapper wxGTK30 netcdf geos postgresql mysql.client blas ]
  -    ++ (with pythonPackages; [ python dateutil wxPython30 numpy ]);
  +    ++ (with python2Packages; [ python dateutil wxPython30 numpy ]);
   
     configureFlags = [
       "--with-proj-share=${proj}/share/proj"
  
positive.code:   postInstall = ''
      wrapProgram $out/bin/grass70 \
      --set PYTHONPATH $PYTHONPATH \
      --set GRASS_PYTHON ${pythonPackages.python}/bin/${pythonPackages.python.executable}
      ln -s $out/grass-*/lib $out/lib
    '';
  
  
negative.code: { stdenv, fetchurl, flex, bison, pkgconfig, zlib, libtiff, libpng, fftw
  , cairo, readline, ffmpeg, makeWrapper, wxGTK30, netcdf, blas
  , proj, gdal, geos, sqlite, postgresql, mysql, python2Packages
  }:
  
  stdenv.mkDerivation {
  