I tried to run a simple local flow and it failed with this error.

RuntimeError: There is no current event loop in thread 'AnyIO worker thread'.

Inside one of my tasks, I am using asynio and aiohttp to request some data from a RestAPI.

hi @Volker L - can you share your flow and how you tried to run it?

Sure. But I am using two of my one libraries, which makes it a bit complicated. I can try to set up a simple example flow, which might also fail 🙂

okay! feel free to share what you can and I'll do my best to help

Ok. Writing a simple example, I was able to figured out what the problem is/was. 🙂 Here is the example:

from parallel_requests import parallel_requests, parallel_requests_async
from prefect import task, flow


@task
def download(urls):
    return parallel_requests(urls)

@task
async def download_async(urls):
    return await parallel_requests_async(urls)

@flow
def run():
    
    urls = ["<https://query2.finance.yahoo.com/v7/finance/quote?symbols=AAPL>"]*10
    res = download_async(urls)
    print(res[0])
    
    
if __name__=='__main__':
    run()

The library

parallel_requests

uses asyncio to run async functions. That seems to be not compatible with

AnyIO

(which prefect is using??). When I switch to

parallel_requests_async

, the flow is running without any problems. Note:

parallel_requests

is my own lib, which you can find here: https://github.com/legout/parallel-requests

glad you figured it out!

AnyIO

(which prefect is using??).

yep! if you're curious how anyio is being used, you can check out this and/or this