Got you. PyPI library makes sense. On Tue, Nov 14, 2017 at 5:27 PM Mark E. Haase <mehaase@gmail.com> wrote:
I'm not asking to change Python's default behavior. I'm asking if anybody else likes this idea, has ideas to make it better, and would use it if I published some form of it on PyPI.
On Tue, Nov 14, 2017 at 10:08 AM, Andrew Svetlov <andrew.svetlov@gmail.com
wrote:
AFAIK Python never hides stdlib codelines in tracebacks. Why we should start to do it in asyncio?
On Tue, Nov 14, 2017 at 4:54 PM Mark E. Haase <mehaase@gmail.com> wrote:
If an exception is thrown while the `asyncio` event loop is running, the stack trace is pretty complicated. Here's an example:
Traceback (most recent call last): File "sample_client.py", line 616, in <module> loop.run_until_complete(main_task) File "/usr/lib/python3.6/asyncio/base_events.py", line 437, in run_until_complete self.run_forever() File "/usr/lib/python3.6/asyncio/base_events.py", line 405, in run_forever self._run_once() File "/usr/lib/python3.6/asyncio/base_events.py", line 1382, in _run_once handle._run() File "/usr/lib/python3.6/asyncio/events.py", line 126, in _run self._callback(*self._args) File "/usr/lib/python3.6/asyncio/tasks.py", line 315, in _wakeup self._step() File "/usr/lib/python3.6/asyncio/tasks.py", line 239, in _step result = coro.send(None) File "sample_client.py", line 319, in main await actions[args.action](args, socket) File "/usr/lib/python3.6/asyncio/coroutines.py", line 105, in __next__ return self.gen.send(None) File "sample_client.py", line 558, in sync_job await asyncio.sleep(args.delay) File "/usr/lib/python3.6/asyncio/coroutines.py", line 105, in __next__ return self.gen.send(None) File "/usr/lib/python3.6/asyncio/tasks.py", line 522, in sleep future, result) File "/usr/lib/python3.6/asyncio/base_events.py", line 525, in call_later timer = self.call_at(self.time() + delay, callback, *args) File "/usr/lib/python3.6/asyncio/base_events.py", line 541, in call_at timer = events.TimerHandle(when, callback, args, self) File "/usr/lib/python3.6/asyncio/events.py", line 148, in __init__ super().__init__(callback, args, loop) File "/usr/lib/python3.6/asyncio/events.py", line 92, in __init__ self._source_traceback = traceback.extract_stack(sys._getframe(1)) File "/usr/lib/python3.6/traceback.py", line 207, in extract_stack stack = StackSummary.extract(walk_stack(f), limit=limit) File "/usr/lib/python3.6/traceback.py", line 352, in extract filename, lineno, name, lookup_line=False, locals=f_locals)) KeyboardInterrupt
Most of the stack frames are inside asyncio (_run, _wakeup, _step) and reveal the mechanics of the event loop. The stack trace would be a lot easier to read (and more similar to a stack trace of an equivalent synchronous program) if it looked like this:
Traceback (most recent call last): File "sample_client.py", line 616, in <module> loop.run_until_complete(main_task) ... File "sample_client.py", line 319, in main await actions[args.action](args, socket) ... File "sample_client.py", line 558, in sync_job await asyncio.sleep(args.delay) KeyboardInterrupt
I recognize that the event loop mechanics are probably useful in some circumstances, but in my experience working with asyncio for the last year, I've found the stack traces are generally too noisy. For a while, I was pasting stack traces into a text editor and cleaning them up by hand, but a few months ago I wrote a custom excepthook that generates stack traces similar to the one above.
def async_excepthook(type_, exc, tb): cause_exc = None cause_str = None
if exc.__cause__ is not None: cause_exc = exc.__cause__ cause_str = 'The above exception was the direct cause ' \ 'of the following exception:' elif exc.__context__ is not None and not exc.__suppress_context__: cause_exc = exc.__context__ cause_str = 'During handling of the above exception, ' \ 'another exception occurred:'
if cause_exc: async_excepthook(type(cause_exc), cause_exc, cause_exc.__traceback__)
if cause_str: print('\n{}\n'.format(cause_str))
print('Async Traceback (most recent call last):') for frame in traceback.extract_tb(tb): head, tail = os.path.split(frame.filename) if (head.endswith('asyncio') or tail == 'traceback.py') and \ frame.name.startswith('_'): print(' ...') continue print(' File "{}", line {}, in {}' .format(frame.filename, frame.lineno, frame.name)) print(' {}'.format(frame.line)) print('{}: {}'.format(type_.__name__, exc))
The meat of it is towards the bottom, "if head.endswith('asyncio')..."There are a lot of debatable details and this implementation is pretty hacky and clumsy, but I have found it valuable in my own usage, and I haven't yet missed the omitted stack frames.
I'm posting here to get constructive criticism on the concept and would also like to hear if Curio or Trio have done anything like this. (Based on a quick skim of the docs, I don't think they are.) I might publish a PyPI package if anybody is interested.
Cheers, Mark _______________________________________________ Async-sig mailing list Async-sig@python.org https://mail.python.org/mailman/listinfo/async-sig Code of Conduct: https://www.python.org/psf/codeofconduct/
-- Thanks, Andrew Svetlov
-- Thanks, Andrew Svetlov