"Pickling of objects of classes whose __new__ mandates the use of keyword-only arguments is supported with protocol 4 (using a new opcode NEWOBJ_EX)."

Hum, can you please write a short example of such class which can only be pickled by the protocol 4 currently? Just for my information.

I understand that some objects cannot be serialized by pickle with protocol lower than 4, whereas your change makes possible to serialize them on Python 3, and it will be possible to deserialize them on Python 2 and Python 3.

If I understood correctly, the change makes sense.

I reviewed the patch, it looks good to me.