Say I want to execute blocking code in a .rpy file. Can't I just execute all the code in a separate thread? I've found the following code to execute a function in a thread. How could I add a callback to that thread so I could get back the whole html page back from that "notthreadSafe" function and return it to the client (web browser)? from twisted.internet import reactor from twisted.python import threadable threadable.init(1) def notThreadSafe(x): """do something that isn't thread-safe""" # ... def threadSafeScheduler(): """Run in thread-safe manner.""" reactor.callFromThread(notThreadSafe, 3) # will run 'notThreadSafe(3)' # in the event loop _stephan