Initialising p2p_protocol with self.

I got the error stating that `handle_message` missing positional argument `writer` but `writer` is supplied to the function. It seems that `handle_message` can't get `self`, that is p2p_protocol.

https://github.com/dvf/blockchain-book/blob/8642a7b55b1b14be40e243cf004051d4f200d4b5/chapters/chapter_7/funcoin/server.py#L17

I've changed this section to `self.p2p_protocol = p2p_protocol(self)` and it's working as intended. Is this normal or am I missing something?