re-implement asyncio.coroutine like something

my_coroutine.py

import asyncio
import functools
import types


def my_coroutine(func):
    @functools.wraps(func)
    def wrapper(*args, **kwargs):
        result_fut = asyncio.Future()

        gen = func(*args, **kwargs)
        assert isinstance(gen, types.GeneratorType)

        next_fut = next(gen)
        assert isinstance(next_fut, asyncio.Future)

        def _callback(fut):
            result = fut.result()

            if isinstance(result, asyncio.Future):
                result.add_done_callback(result_fut)
                return

            try:
                next_fut = gen.send(result)
            except StopIteration as e:
                result_fut.set_result(e.value)
            else:
                assert isinstance(next_fut, asyncio.Future)
                next_fut.add_done_callback(_callback)

        next_fut.add_done_callback(_callback)

        return result_fut

    return wrapper


def test():
    @my_coroutine
    def sleep_and_done():
        print(3)
        yield from asyncio.sleep(1)
        print(2)
        yield from asyncio.sleep(1)
        print(1)
        yield from asyncio.sleep(1)
        print('done')
        return 42

    loop = asyncio.get_event_loop()
    result = loop.run_until_complete(sleep_and_done())
    assert result == 42

    @my_coroutine
    def coroutine_within_coroutine():
        result = yield from sleep_and_done()
        print(result)

    loop = asyncio.get_event_loop()
    result = loop.run_until_complete(coroutine_within_coroutine())
    assert result is None


if __name__ == '__main__':
    test()

その後色々調べた結果、これは asyncio.tasks.Task のような何かっぽい。