Async is one more attempt to make the definition and execution of asynchronous
interdependent operations easy. For that to work, you may define tasks which
communicate with each other by channels. Channels transfer items, which is very
similar to bytes flowing through pipes uses in inter-process communication.
Items will only be generated on demand, that is when you read from the
respective output channel.

WWW: http://packages.python.org/async/intro.html