Asyncio exception handling breaks convention by logging callback parameter values

[CendioZeijlon]

Bug report

Bug description:

My understanding is that Python usually does not attempt to log or show parameter and variable values when errors occur. It seems uncharacteristic that asyncio does so, e.g. when it handles uncaught exceptions.

This type of logging can also occur when asyncio reports on tasks with too slow execution times, but then only in debug mode.

When not in debug mode, parameter values are logged for uncaught exceptions, but not for slow execution times. I don't see why these two cases behave differently. If you think that this logging is necessary, perhaps it can be limited to debug mode only?

Input:

import asyncio
import functools

loop = asyncio.new_event_loop()
asyncio.set_event_loop(loop)

def test_callback(a, b, c, *, x, y, z):
    raise RuntimeError('Some uncaught error')

loop.call_soon(
    functools.partial(
        test_callback,
        {'key': 'value'},
        ['value'],
        ('value',),
        x = {'key': 'value'},
        y = ['value'],
        z = ('value',)
    )
)
loop.call_soon(loop.stop)

res = ''
try:
    loop.run_forever()
finally:
    loop.close()

Output:

Exception in callback test_callback({'key': 'value'}, ['value'], ('value',), x={'key': 'value'}, y=['value'], z=('value',))() at /home/aleze/Documents/scenario.py:7
handle: <Handle test_callback({'key': 'value'}, ['value'], ('value',), x={'key': 'value'}, y=['value'], z=('value',))() at /home/aleze/Documents/scenario.py:7>
Traceback (most recent call last):
  File "/usr/lib64/python3.11/asyncio/events.py", line 80, in _run
    self._context.run(self._callback, *self._args)
  File "/home/aleze/Documents/scenario.py", line 8, in test_callback
    raise RuntimeError('Some uncaught error')
RuntimeError: Some uncaught error

Extra:

The function that actually creates the output is format_helpers._format_args_and_kwargs().

CPython versions tested on:

3.12

Operating systems tested on:

Linux

Linked PRs

• gh-112997: Don't log arguments in asyncio unless debugging #115667

[CendioOssman]

Note that this is a potential security issue, as you would not expect the contents of your sensitive variables to leak out this easily.

[gvanrossum]

I think it's reasonable to restrict this to debug mode. Could one of you submit a PR?