I understand the arguments for using the newer TaskGroup in place of older mechanisms based on create_task().
However, TaskGroup exits after all tasks are done. What if you want to start processing the results as soon as the first task finishes, like you can with asyncio.as_completed() or asyncio.wait( ..., return_when=FIRST_COMPLETED )?
If TaskGroup offers no way to do that, then it's a trade-off rather than a strict upgrade, isn't?
A callback based solution:
import asyncio
def task_done(task):
try:
value = task.result()
msg = f"finished, return value: {value}"
except asyncio.CancelledError as err:
msg = "cancelled"
except Exception as err:
msg = f"failed: {repr(err)}"
print(f"{task.get_name()} {msg}")
async def coro(i):
await asyncio.sleep(i)
if i == 4:
1/0
return 100 + i
async def main():
try:
async with asyncio.TaskGroup() as tg:
for i in range(1, 10):
task = tg.create_task(coro(i), name=f"task #{i}")
task.add_done_callback(task_done)
except ExceptionGroup as group:
print(f"{len(group.exceptions)} exception(s) in the task group")
if __name__ == '__main__':
asyncio.run(main())
Total output:
task #1 finished, return value: 101
task #2 finished, return value: 102
task #3 finished, return value: 103
task #4 failed: ZeroDivisionError('division by zero')
task #8 cancelled
task #9 cancelled
task #7 cancelled
task #6 cancelled
task #5 cancelled
1 exception(s) in the task group