gistfile1.txt

1. See implementation here: https://gist.github.com/3891601
2. Python 2 code:

@gen.async
def long_op(a):
    if a == 1:
        yield gen.Task(io_loop.add_timeout, time() + 0.1)
        gen.ret(a)
    
    yield gen.Task(io_loop.add_timeout, time() + 0.1)
    gen.ret(a * 10)

3. With vanilla tornado.gen it looks like:

@gen.engine
def long_op(a, callback):
    if a == 1:
        yield gen.Task(io_loop.add_timeout, time() + 0.1)
        callback(a)
        return

    yield gen.Task(io_loop.add_timeout, time() + 0.1)
    callback(a * 10)

4. Starting with Python 3.3, you can use return with argument - it will raise StopIteration

@gen.async
def long_op(a):
    if a == 1:
        yield gen.Task(io_loop.add_timeout, time() + 0.1)
        return a

    yield gen.Task(io_loop.add_timeout, time() + 0.1)
    return a * 10

5. Obviously you can mix gen.engine and gen.async if you want to run callbacks explicitly or implicitly.