How do I use Deferreds to make my blocking code non-blocking?
You don’t. Deferreds don’t magically turn a blocking function call into a non-blocking one. A Deferred is just a simple object that represents a deferred result, with methods to allow convenient adding of callbacks. (This is a common misunderstanding; suggestions on how to make this clearer in the Deferred Execution howto are welcome!) If you have blocking code that you want to use non-blockingly in Twisted, either rewrite it to be non-blocking, or run it in a thread. There is a convenience function, deferToThread, to help you with the threaded approach — but be sure to read Using Threads in Twisted.
