[英]python asyncio exceptions raised from loop.create_task()
[英]Gathering results from an asyncio task list with exceptions
編碼...
import asyncio
import random
from time import perf_counter
from typing import Iterable
from pprint import pprint
async def coro(n, i, threshold=0.4):
await asyncio.sleep(i)
if i > threshold:
# For illustration's sake - some coroutines may raise,
# and we want to accomodate that and just test for exception
# instances in the results of asyncio.gather(return_exceptions=True)
raise Exception(f"{i} of Task-{n} is too high")
return i
async def main(it: Iterable, timeout: float) -> tuple:
tasks = [asyncio.create_task(coro(i+1, d), name=f"Task-{i+1}") for i, d in enumerate(it)]
await asyncio.wait(tasks, timeout=timeout)
return tasks # *not* (done, pending)
timeout = 0.5
random.seed(444)
n = 10
it = [random.random() for _ in range(n)]
start = perf_counter()
tasks = asyncio.run(main(it=it, timeout=timeout))
elapsed = perf_counter() - start
print(f"Done main({n}) in {elapsed:0.2f} seconds\n")
pprint(tasks)
print('----')
# does not work from here on....
res = []
for t in tasks:
try:
r = t.result() # gives an error!!!
except Exception as e:
res.append(e)
else:
res.append(r)
pprint(res)
...不適用於收集任務結果。 它失敗了...
Traceback (most recent call last):
File "c:\Users\user\Documents\user\projects\learn\asyncio\wrap_gather_in_timeout.py", line 8, in coro
await asyncio.sleep(i)
File "C:\Users\user\AppData\Local\Programs\Python\Python39\lib\asyncio\tasks.py", line 654, in sleep
return await future
asyncio.exceptions.CancelledError
During handling of the above exception, another exception occurred:
Traceback (most recent call last):
File "c:\Users\user\Documents\user\projects\learn\asyncio\wrap_gather_in_timeout.py", line 35, in <module>
r = t.result()
asyncio.exceptions.CancelledError
Task exception was never retrieved
future: <Task finished name='Task-7' coro=<coro() done, defined at c:\Users\user\Documents\user\projects\learn\asyncio\wrap_gather_in_timeout.py:7> exception=Exception('i too high')>
Traceback (most recent call last):
File "c:\Users\user\Documents\user\projects\learn\asyncio\wrap_gather_in_timeout.py", line 13, in coro
raise Exception("i too high")
Exception: i too high
該代碼在 python 3.9 中運行。 知道我哪里出錯了,為什么?
是不是因為任務拋出異常后需要取消? 我無法成功實施它。
您的代碼有效,您無法成功創建res
的問題是因為代碼不會引發正常的Exception
class。 由於任務失敗,它最終會調用asyncio.exceptions.CancelledError
,如果我們查看文檔,它繼承自BaseException
而不是Exception
。 自 Python 3.8 起,此更改是新的,並且由於您使用的是 Python 3.9,因此該更改已生效。 將您的代碼稍微更改為以下結果:
res = []
for t in tasks:
try:
r = t.result() # gives an error!!!
except BaseException as e:
res.append(e)
continue
res.append(r)
print(res)
[0.3088946587429545,
0.01323751590501987,
Exception('0.4844375347808497 of Task-3 is too high'),
asyncio.exceptions.CancelledError(),
asyncio.exceptions.CancelledError(),
asyncio.exceptions.CancelledError(),
Exception('0.4419557492849159 of Task-7 is too high'),
0.3113884366691503,
0.07422124156714727,
asyncio.exceptions.CancelledError()]
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