anchor.diff:      ++ 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.
  
positive.code:       C_INCLUDE_PATH = concatStringsSep ":" (map (p: "${p}/include") buildInputs);
        LIBRARY_PATH = concatStringsSep ":" (map (p: "${p}/lib") buildInputs);
  
        configurePhase = "true";
  
        buildPhase =
          ''
  
negative.code: 
      configureFlags = "--enable-shared --with-threads --enable-unicode --with-wctype-functions";
  
      preConfigure = "${ensurePurity}" + 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
  