> I vote -1 to adding a new flag to control whether it returns zero or
> raises and +0 to just fixing it in Python 3.5 (I don't think returning
> zero is an unreasonable thing to do; it's not obvious to me from
> send(2) that it is guaranteed to never return zero although I believe
> that to be the case).  It'll break Tornado, but there will be plenty
> of time to get a fix out before then.

If that's your opinion then I'm inclined to trust you.

> Another option may be to have SSLSocket.send() convert the WANT_WRITE
> exception into a socket.error with errno EAGAIN. 

I don't think it's a good idea, since it hides the true reason of the
error (also, it suppresses the distinction between WANT_READ and
WANT_WRITE, which tells you whether you need to select() the socket for
reading or writing).