anchor.diff:  }:
   
   let
  -  inherit (stdenv.lib)
  +  inherit (lib)
       optionalString;
   
  -  version = "1.14.0";
  +  version = "1.15.4";
   in
   buildPythonPackage rec {
     name = "pycairo-${version}";
   
     src = fetchurl {
  -    url = "https:/github.com/pygobject/pycairo/releases/download/v${version}/pycairo-${version}.tar.gz";
  +    url = "https:/github.com/pygobject/pycairo/releases/download/v${version}/"
  +      + "pycairo-${version}.tar.gz";
       hashOutput = false;
  -    sha256 = "6903729a473a3de2c3b914746f737e15890076feb18b59cacdcff6c032225cff";
  +    sha256 = "ee4c3068c048230e5ce74bb8994a024711129bde1af1d76e3276c7acd81c4357";
     };
   
     buildInputs = [
  
positive.code: 
    # pkgconfig has a broken prefix
    preFixup = ''
      sed -i "s,prefix=.*,prefix=$out," $out/lib/pkgconfig/*.pc
    '';
  
    passthru = {
  
negative.code:     };
    };
  
    meta = with lib; {
      description = "Python bindings for the cairo library";
      homepage = http://cairographics.org/pycairo/;
      license = with licenses; [
  