Added brackets to list comprehension, fixing this exception:

[ricardopinto]

Exception ignored in: <generator object _find_first_app_frame_and_name.<locals>.<genexpr> at 0x10693ad00>
Traceback (most recent call last):
  File "/Users/ricardopinto/a_project/env/lib/python3.6/site-packages/structlog/_frames.py", line 42, in <genexpr>
    while any(name.startswith(i) for i in ignores):
SystemError: error return without exception set

From what I saw, ignores was ['structlog', 'logging'], and name was structlog._frames.
Python version is 3.6.5, structlog is 18.1.0.

[codecov]

Codecov Report

Merging #174 into master will not change coverage.
The diff coverage is 100%.

@@          Coverage Diff          @@
##           master   #174   +/-   ##
=====================================
  Coverage     100%   100%           
=====================================
  Files          13     13           
  Lines         822    822           
  Branches      106    106           
=====================================
  Hits          822    822

Impacted Files	Coverage Δ
src/structlog/_frames.py	100% <100%> (ø)	⬆️

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[hynek]

I’d need to see a breaking test for the old code.

IMHO the code itself should be fine: it’s generator which is more effective than a list comprehension but if it’s broken, we need a regression test to make sure the error doesn’t come back.

Out of curiosity, is numpy involved? Googling that error brings up a bunch of it.

[ricardopinto]

I tried to pinpoint the code that triggers the issue, but to no avail. There's plenty of threads and processes in execution time, and it seemed to happen when we created a thread that enqueued a message on a periodic basis, it had nothing related to logging, numpy or anything complex. I even reduced all its code to a simple return statement and the issue still happened. If we don't start the thread, no error happens.

class PeriodicTrigger(Thread):
    def __init__(self, queue: Queue, interval: float):
        super(PeriodicTrigger, self).__init__()
        self.queue: Queue = queue
        self.interval: float = interval
        self.should_stop: bool = False

    def run(self):
        while not self.should_stop:
            now: float = time()
            next_run_at = now + self.interval
            sleep(next_run_at - now)
            self.queue.put('a_message')

As you can see, there's nothing particular about this thread.

Numpy is indeed a requirement, but I couldn't see any direct relationship in the traces or code.
I agree the generator should work just fine, but this was the only way to prevent the issue from happening.

[hynek]

Looks like we’re not the only ones with this problem: psf/requests#4567

It seems like there’s something weird going on with frames, C extensions and threads. The unholy trifecta. :)

Would you mind changing [] to tuple() and see if it helps too? They’re a bit more efficient.

[hynek]

Bump? 😇

[techdragon]

I'm getting quite a lot of log noise due to exceptions in this generator, so fixing this would be very welcome.

[hynek]

@techdragon would you mind to test whether the proposed solution with tuple() instead of [] works then?

[ricardopinto]

@hynek I tried tuple() instead of [] and it worked. Want me to update the code in the PR?

[hynek]

That would be swell!

[ricardopinto]

@hynek done. Happy new year!

[hynek]

thanks and sorry for the delays!

[ricardopinto]

Excellent, thanks!

[methane]

@ricardopinto Sorry for asking about old issue, but do you remember that you did use PyCharm?

It seems there was a bug in PyCharm and python raised SystemErro during genexpr.

https://stackoverflow.com/questions/50369959/systemerror-error-return-without-exception-set-when-using-requests-and-debugge/52054289#52054289

https://stackoverflow.com/questions/50055316/flask-upgrade-lots-of-exception-ignored-in-messages-in-console

ContinuumIO/anaconda-issues#8737

[ricardopinto]

@ricardopinto Sorry for asking about old issue, but do you remember that you did use PyCharm?

It seems there was a bug in PyCharm and python raised SystemErro during genexpr.

https://stackoverflow.com/questions/50369959/systemerror-error-return-without-exception-set-when-using-requests-and-debugge/52054289#52054289

https://stackoverflow.com/questions/50055316/flask-upgrade-lots-of-exception-ignored-in-messages-in-console

ContinuumIO/anaconda-issues#8737

Hi. Yes, I was using PyCharm when I got that error.

[methane]

Thank you. I am relieved to hear that.
There is no unsolved multithread+genexpr issue in cpython.