Call an async function from a sync function called by an async function

Question

I have this configuration

async def A():
    B()

async def C():
    # do stuff

def B():
    # do stuff
    r = C()
    # want to call C() with the same loop and store the result

asyncio.run(A())

I don't really know how to do that. I tried this by reading some solutions on the web:

def B():
    task = asyncio.create_task(C())
    asyncio.wait_for(task, timeout=30)
    result = task.result()

But it doesn't seem to work...

Why do not make the B async and await it in A? In that case, you could be able to invoke r = await C() in B. — Artyom Vancyan
– Artyom Vancyan, Commented Oct 16, 2022 at 7:31
Because B() is actually called by both async and non-async functions — graille
– graille, Commented Oct 16, 2022 at 15:27
stackoverflow.com/questions/70231451/…. The idea is to start a second thread that runs the coroutine C() and returns the result. Then instead of simply calling C() in your function B(), you do r = asyncio.run_coroutine_threadsafe(C(), loop).result(). — Paul Cornelius
– Paul Cornelius, Commented Oct 17, 2022 at 22:59
Does B actually need to access the result or just return it? — MisterMiyagi
– MisterMiyagi, Commented Oct 18, 2022 at 14:18

frisko · Accepted Answer · 2022-10-17 06:17:09Z

0

Since asyncio does not allow its event loop to be nested, you can use nest_async library to allow nested use of asyncio.run and asyncio.run_until_complete methods in the current event loop or a new one:

First, install the library:

pip install nest-asyncio

Then, add the following to the beginning of your script:

import nest_asyncio

nest_asyncio.apply()

And the rest of the code:

async def A():
    B()

async def C():
    # do stuff

def B():
    # do stuff
    loop = asyncio.get_event_loop()
    result = loop.run_until_complete(C())
    # want to call C() with the same loop and store the result

asyncio.run(A())

edited Oct 17, 2022 at 6:17

answered Oct 16, 2022 at 3:02

frisko

8759 silver badges14 bronze badges

Sign up to request clarification or add additional context in comments.

3 Comments

graille Over a year ago

No I can't, I get the error "RuntimeError: This event loop is already running". Since asyncio doesn't support nested loop

frisko Over a year ago

@graille Is it necessary to be in the current running loop? What if you could run it in a new event loop?

graille Over a year ago

You cannot launch a new loop when a loop is already running: "RuntimeError: Cannot run the event loop while another loop is running"

Collectives™ on Stack Overflow

Call an async function from a sync function called by an async function

1 Answer 1

3 Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

3 Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related