python runtime_error ai_generated true

Task exception was never retrieved future: <Task finished name='Task-5' coro=<fetch() done, defined at app.py:42> exception=ValueError('bad payload')>

ID: python/asyncio-task-exception-was-never-retrieved

Also available as: JSON · Markdown · 中文
80%Fix Rate
88%Confidence
0Evidence
2024-07-19First Seen

Version Compatibility

VersionStatusIntroducedDeprecatedNotes
3.8 active — — —
3.9 active — — —
3.10 active — — —
3.11 active — — —
3.12 active — — —

Root Cause

A task created with asyncio.create_task() raised an exception, but nobody awaited the task or called task.exception(), so the exception is logged as a warning at garbage collection.

generic

中文

使用 asyncio.create_task() 创建的任务抛出异常，但无人 await 该任务或调用 task.exception()，导致异常在垃圾回收时以警告形式记录。

Workarounds

  1. 90% success 
    tasks = [asyncio.create_task(fetch(u)) for u in urls]
results = await asyncio.gather(*tasks, return_exceptions=True)
for r in results:
    if isinstance(r, Exception):
        logging.exception('task failed', exc_info=r)
  2. 87% success 
    def _on_done(t: asyncio.Task):
    if not t.cancelled() and t.exception():
        logging.error('task error', exc_info=t.exception())

t = asyncio.create_task(fetch(u))
t.add_done_callback(_on_done)

Dead Ends

Common approaches that don't work:

  1. 85% fail

    Hides the symptom but the task still fails silently and the error is lost.

  2. 80% fail

    Swallows real errors and produces no diagnostic; debugging becomes impossible.