Attempting to use py3 async-await with existing callback api

async-drive.py

from types import coroutine

class CbWait(object):

    def __init__(self):
        self.coro = None
        self.args = None

    def recur(self, coro):
        if self.args:
            coro.send(self.args).recur(coro)
        else:
            self.coro = coro

    def cb(self, *a):
        if self.coro:
            self.coro.send(a).recur(self.coro)
        else:
            self.args = a

    @property
    @coroutine
    def result(self):
        return (yield self)

def spawn(coro):
    coro.send(None).recur(coro)

ext_cb = None

def syscall(cb):
    global ext_cb
    ext_cb = cb

async def f():
    while True:
        w = CbWait()
        syscall(w.cb)
        v, = await w.result
        print(v)

spawn(f())
for i in range(5):
    ext_cb(i)