如何在 Python/Asyncio 中处理未处理的异常？

Question

I have a task.

async def task():
    # stuff

I have my coroutine

async def coro(tasks):
    tasks = [asyncio.create_task(t) for t in tasks]
    task_iterator = tqdm(asyncio.as_completed(tasks), total=len(tasks))
    result = [await t for t in task_iterator]
    return result

I run it as

try:
    asyncio.run(coro)
except Exception as e:
    # handle error

The issue is that if task() fails, I get two errors. One error complains that unhandled exception in asyncio.run() shutdown task , and the other complains that task exception was never retrieved future . Both error messages point to something that happened in task() .

My questions are

1. Why does the try...except clause aorund asyncio.run() not catch these two issues?

2. What can I do to catch them?

Answer 1

1. You're not running the coro in your main thread, but in the asyncio's runner. Each task (a function call with some arguments) is pushed to the back of an execute queue where they'll be popped once there's no other tasks executing. Each task will leave the executing state as soon as it needs some I/O. There the task will be pushed to waiting queue and the if the asyncio's event loop catches the corresponding I/O action for that task it'll move the task to the executing queue. Summing up: While some tasks are waiting for I/O, other(s) can run the non-I/O parts. That's why it's called async io .

2. You may use a decorator around the coro function and handle the exceptions there. Something like:

def exception_handler(f):
   async def wrapper(*args, **kwargs):
      try:
         return await f(*args, **kwargs)
      except Exception as e:
         print(e)
   return wrapper


@exception_handler
async def coro(tasks):
   ...


asyncio.run(coro, args=([1, 2, 3], ))