Inconsistent behavior with KeyboardInterrupt and asyncio futures

[MichelDesmoulin]

BPO	26455
Nosy	@gvanrossum, @1st1, @mvolfik

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

Show more details

GitHub fields:

assignee = None
closed_at = <Date 2016-09-09.18:41:34.286>
created_at = <Date 2016-02-28.19:50:26.943>
labels = ['type-bug', 'expert-asyncio']
title = 'Inconsistent behavior with KeyboardInterrupt and asyncio futures'
updated_at = <Date 2021-02-01.20:53:20.483>
user = 'https://bugs.python.org/MichelDesmoulin'

bugs.python.org fields:

activity = <Date 2021-02-01.20:53:20.483>
actor = 'vstinner'
assignee = 'none'
closed = True
closed_date = <Date 2016-09-09.18:41:34.286>
closer = 'gvanrossum'
components = ['asyncio']
creation = <Date 2016-02-28.19:50:26.943>
creator = 'Michel Desmoulin'
dependencies = []
files = []
hgrepos = []
issue_num = 26455
keywords = []
message_count = 4.0
messages = ['260984', '275380', '386087', '386088']
nosy_count = 4.0
nosy_names = ['gvanrossum', 'yselivanov', 'Michel Desmoulin', 'mvolfik']
pr_nums = []
priority = 'normal'
resolution = 'third party'
stage = None
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue26455'
versions = ['Python 3.5']

[MichelDesmoulin]

If you trigger KeyboardInterrupt in a coroutine and catch it, the program terminates cleanly:

import asyncio

async def bar():
    raise KeyboardInterrupt

loop = asyncio.get_event_loop()

try:
loop.run_until_complete(bar())
except KeyboardInterrupt:
print("It's ok")
finally:
loop.stop()
loop.close()

This outputs:

It's ok

However, if you wrap the coroutine in a Task, you will get a mixed behavior:

try:
task = asyncio.ensure_future(bar())
loop.run_until_complete(task)
except KeyboardInterrupt:
print("It's ok")

This outputs:

It's ok
Task exception was never retrieved
future: <Task finished coro=<bar() done, defined at ki_bug.py:4> exception=KeyboardInterrupt()>
Traceback (most recent call last):
  File "ki_bug.py", line 10, in <module>
    loop.run_until_complete(main_future)
  File "/usr/lib/python3.5/asyncio/base_events.py", line 325, in run_until_complete
    self.run_forever()
  File "/usr/lib/python3.5/asyncio/base_events.py", line 295, in run_forever
    self._run_once()
  File "/usr/lib/python3.5/asyncio/base_events.py", line 1258, in _run_once
    handle._run()
  File "/usr/lib/python3.5/asyncio/events.py", line 125, in _run
    self._callback(*self._args)
  File "/usr/lib/python3.5/asyncio/tasks.py", line 239, in _step
    result = coro.send(None)
  File "ki_bug.py", line 5, in bar
    raise KeyboardInterrupt
KeyboardInterrupt

We have several contradictory behaviors: the KeyboardInterrupt is raised, and captured by the future (since your can do task.exception() to suppress the stracktrace) but also catched by except while the program is allowed to continue, yet still the stack trace is displayed and eventually the program return code will be 0.

It's very confusing.

[gvanrossum]

Closing this issue in favor of the upstream one: python/asyncio#341

[mvolfik]

python/asyncio is archived now and there is no definitive resolution, nor a concrete workaround in that thread. has this progressed elsewhere? or is it still unresolved?

could anyone please show sample workaround code? (i need to call some cleanup code which still runs in the context of the event loop)

---

also, I was unable to login to this bug tracker with GitHub, because my name contains non-ascii characters. where should I report that :D ?

[gvanrossum]

If you just need help, I recommend https://discuss.python.org/c/users/7

If you still have an issue with ^C, open a new issue.