anchor.diff: -{ stdenv, buildPythonPackage, darwin, grpc
  -, six, protobuf, enum34, futures, isPy27, pkgconfig
  -, cython, c-ares, openssl, zlib }:
  +{ stdenv
  +, buildPythonPackage
  +, darwin
  +, grpc
  +, six
  +, protobuf
  +, enum34
  +, futures
  +, isPy27
  +, pkg-config
  +, cython
  +, c-ares
  +, openssl
  +, zlib
  +}:
   
   buildPythonPackage rec {
     inherit (grpc) src version;
  
positive.code:   GRPC_PYTHON_BUILD_SYSTEM_ZLIB = 1;
    GRPC_PYTHON_BUILD_SYSTEM_CARES = 1;
  
    meta = with stdenv.lib; {
      description = "HTTP/2-based RPC framework";
      license = licenses.asl20;
      homepage = "https://grpc.io/grpc/python/";
      maintainers = with maintainers; [ ];
    };
  }
  
negative.code: 
    outputs = [ "out" "dev" ];
  
    nativeBuildInputs = [ cython pkg-config ]
      ++ stdenv.lib.optional stdenv.isDarwin darwin.cctools;
  
    buildInputs = [ c-ares openssl zlib ];
    propagatedBuildInputs = [ six protobuf ]
      ++ stdenv.lib.optionals (isPy27) [ enum34 futures ];
  
    preBuild = stdenv.lib.optionalString stdenv.isDarwin "unset AR";
  
  