為什么python3.6可以從非協程生成器中的協程對象產生？

Question

zz.py

import asyncio

# @asyncio.coroutine
def main():
    yield from asyncio.sleep(1)

next(main())

• 在 Python 3.6.7 中執行 --> 好的，沒有錯誤。

• 在 Python 3.7.3 中執行 --> NOT OK，接下來報告：

   zz.py:5: RuntimeWarning: coroutine 'sleep' was never awaited yield from asyncio.sleep(1) RuntimeWarning: Enable tracemalloc to get the object allocation traceback Traceback (most recent call last): File "zz.py", line 7, in <module> next(main()) File "zz.py", line 5, in main yield from asyncio.sleep(1) TypeError: cannot 'yield from' a coroutine object in a non-coroutine generator

我知道我可以啟用@asyncio.coroutine使兩者都工作，或者async/await 。

但是，這里我的問題是：如果我仍然使用generator ，那么 python3.6 和 python3.7 有什么區別？ 我真的覺得這里很混亂。

Answer 1

深入python源代碼后，我找到了根本原因：

• 在 python3.6 中，雖然async/await已經存在，但是coroutine.sleep仍然使用generator based coroutine ：

   @coroutine def sleep(delay, result=None, *, loop=None): """Coroutine that completes after a given time (in seconds).""" if delay == 0: yield return result if loop is None: loop = events.get_event_loop() future = loop.create_future() h = future._loop.call_later(delay, futures._set_result_unless_cancelled, future, result) try: return (yield from future) finally: h.cancel()

• 在python3.7中， coroutine.sleep開始切換到native coroutine ：

   async def sleep(delay, result=None, *, loop=None): """Coroutine that completes after a given time (in seconds).""" if delay <= 0: await __sleep0() return result if loop is None: loop = events.get_event_loop() future = loop.create_future() h = loop.call_later(delay, futures._set_result_unless_cancelled, future, result) try: return await future finally: h.cancel()

所以，當python3.6 yield from asyncio.sleep(1)執行yield from asyncio.sleep(1)時，它實際上並沒有從原生協程中yield，肯定沒有錯誤。