> I prefer coroutines over state machines

And that's why Python supports `asyncio` (not to be confused with `asyncore` which is obsolete). So I prefer:

  sock = yield from connect('localhost', 7942)
  msg = yield from read_message(sock)
  print(msg)

to this callback hell:

  connect('localhost', 7942, function(sock) {
      read_message(sock, function(msg)) {
          console.log(msg);
      });
  });

And they're completely equivalent. Why would someone actually like the latter, except you're forced to use it because of the prevalence of JavaScript?

`asyncio` is not only easier to use than the traditional "manual" state machines with classes, but also much faster than something like `Twisted`. In my crappy local benchmark[1], it easily beat `Twisted` in a considerable margin. That may be because of the flaws in my test code, but still their performance is on par. I see no points in relying on callback hell, at least in Python, except the lack of the libraries that support asyncio, which makes me a little bit sad.

[1] https://github.com/barosl/ws-bench