anchor.diff:    inherit buildInputs;
     C_INCLUDE_PATH = concatStringsSep ":" (map (p: "${p}/include") buildInputs);
     LIBRARY_PATH = concatStringsSep ":" (map (p: "${p}/lib") buildInputs);
  -  
     configureFlags = "--enable-shared --with-wctype-functions";
     
     preConfigure = ''
  
positive.code: 
  in
  
  stdenv.mkDerivation {
    name = "python-2.5.4";
    
    src = fetchurl {
  
negative.code:     opensslSupport = openssl != null;
      tkSupport = (tk != null) && (tcl != null);
      libPrefix = "python2.5";
    } ;
  } // (if stdenv.system == "i686-darwin" then { NIX_CFLAGS_COMPILE = "-msse2" ; } else {} ) )
  