anchor.diff:  
       configureFlags = "--enable-shared --with-threads --enable-unicode --with-wctype-functions";
   
  -    preConfigure =
  +    preConfigure = "${ensurePurity}" + optionalString stdenv.isCygwin
         ''
  -        # Purity.
  -        for i in /usr /sw /opt /pkg; do
  -          substituteInPlace ./setup.py --replace $i /no-such-path
  -        done
  -      '' + optionalString stdenv.isCygwin ''
           # On Cygwin, `make install' tries to read this Makefile.
           mkdir -p $out/lib/python${majorVersion}/config
           touch $out/lib/python${majorVersion}/config/Makefile
  
positive.code:       C_INCLUDE_PATH = concatStringsSep ":" (map (p: "${p}/include") buildInputs);
        LIBRARY_PATH = concatStringsSep ":" (map (p: "${p}/lib") buildInputs);
  
        configurePhase = "true";
  
        buildPhase =
          ''
  
negative.code:     ++ optional zlibSupport zlib
      ++ optionals stdenv.isDarwin [ darwinArchUtility darwinSwVersUtility ];
  
    ensurePurity =
      ''
        # Purity.
        for i in /usr /sw /opt /pkg; do
          substituteInPlace ./setup.py --replace $i /no-such-path
        done
      '';
  
    # Build the basic Python interpreter without modules that have
    # external dependencies.
  