Why in async iterator give errror: RuntimeError: Task got bad yield: 1

Question

I am new in Asynchronous Python. I study the behavior of asynchronous iterators. I do everything as written by pep492. But get it RuntimeError: Task got bad yield: 1. Help please understand what i do wrong. On this site, I read about this error but did not understand anything

class Awaitable:
    def __await__(self):
        i = 1
        while i < 3:
            yield i
            print("yield {}".format(i))
            i +=1
        return i

class AsyncIterator:

    def __aiter__(self):
        return self

    async def __anext__(self):
        try:
            value = await Awaitable()
        except StopIteration:
            raise StopAsyncIteration
        return value

i = AsyncIterator().__aiter__()

async def coro():
    while True:
        try:
            row = await i.__anext__()
            print(row)
        except StopAsyncIteration:
            break
        else:
            print(row)

event_loop = asyncio.get_event_loop()
event_loop.run_until_complete(coro())
.............................................................
  File "C:\Users\mykola\Downloads\async_await.py", line 342, in __await__
    yield i
RuntimeError: Task got bad yield: 1

Possible duplicate of [Python asyncio task got bad yield](https://stackoverflow.com/q/30172821/213550) — VMAtm, Mar 18 '18 at 15:58
unfortunately I do not understand what is being written in these sources that you offered to read. I'm doing everything as it is written in pep-492. In __anext__ corotine after await is Awaitable() object, its method __await__ returns an iterator as it is written pep-492. Сould you fix my code? Maybe then it will become clearer to me — Mykola Fenyk, Mar 22 '18 at 15:32
Basically, you cannot return a value from async function - you need to return a promise — VMAtm, Mar 22 '18 at 15:39
It is a TypeError if __await__ returns anything but an iterator. — Mykola Fenyk, Mar 24 '18 at 21:03

score 0 · Answer 1 · answered Oct 16 '22 at 06:03

0

When you run your code with asyncio then asyncio complains.

It expects you to return Futures from that yield.

The language let's you do it. Asyncio complains here.

See this question Precise specification of __await__

answered Oct 16 '22 at 06:03

Mihai Andrei

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Why in async iterator give errror: RuntimeError: Task got bad yield: 1

1 Answers1