Tornado has a well documented (and least complicated regarding gevent & twisted are concerned IMHO) but not well known/used "inline callback" with yields to simplify async code.

http://www.tornadoweb.org/en/branch2.3/gen.html

From there, I made a wrapper to wrap potentially blocking logic in threads so I could have code that isn't async/non-blocking behave like it was.

https://gist.github.com/anonymous/5190528