Is it possible to use tornado's gen.engine and gen.Task with twisted?

Question

The project I am working on is all written in Tornado, but I have included a bit of Twisted to deal with asynchronous XML-RPC. I was wondering if you can use Tornado\'s gen.engi

Answer 1

Sure - but it's called inlineCallbacks in Twisted:

from twisted.internet.defer import inlineCallbacks

@inlineCallbacks
def foo():
    x = yield bar()
    print x

Answer 2

You can use gen.Task with anything that takes a callback keyword argument. However, Twisted-style code usually returns a Deferred instead of taking a callback as input. You'll need to wrap the Deferred in something tornado.gen can understand (probably a Future). Something like this (untested):

def wrap_deferred(deferred):
    # Could also use concurrent.futures.Future from the standard library,
    # but Tornado's version gives better tracebacks on python 2.
    future = tornado.concurrent.TracebackFuture()
    deferred.addCallbacks(future.set_result, future.set_exception)
    return future

@gen.coroutine
def my_coroutine(self):
    # Use wrap_deferred instead of gen.Task
    x = yield wrap_deferred(some_twisted_function())

Answer 3

I modified Ben's sample code a bit in order to set exception correctly.

def wrap_deferred(deferred):
    future = tornado.concurrent.TracebackFuture()
    deferred.addCallback(future.set_result)
    deferred.addErrback(lambda err: future.set_exception(err.value))
    return future

twisted wrap exception as a failure.Failure. future.set_exception complains it is not an exception type.