CODEWITHSUNDEEP
pythonpython-3.xpython-asyncio
alt-f4
alt-f4

Reputation: 2306

How can I propagate exceptions from asyncio functions?

I am using asyncio, and I have noticed that exception do not get raised within async functions.

I have created a sample of the problem I am facing, where my async function looks like:

async def async_fun(foo):
    try:
        get_foo = await some_thing_async(bar)
    except Exception as E:
        raise E  # Does not raise exception :(

Which I gather and run like:

async def main():
    await asyncio.gather(async_fun("baz"), return_exceptions=True)


asyncio.run(main())

How can I propagate exceptions from async_fun? I want to be able to raise exceptions if they occur. Happy to provide further information if needed.

Upvotes: 1

Views: 1480

Answers (1)

user4815162342
user4815162342

Reputation: 154856

return_exceptions=True explicitly tells asyncio.gather() to return exceptions raised by awaitables, instead of propagating them which is the default behavior. Since you don't examine the return value of asyncio.gather(), you have no way of noticing the exceptions.

To fix the issue, just remove return_exceptions=True from the invocation of asyncio.gather:

async def main():
    await asyncio.gather(async_fun("baz"))

Also note that if you only await one function, asyncio.gather is unnecessary, so the above could have been written more shortly as await async_fun("baz").

Upvotes: 1

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