Logging statement using 'threadName' from concurrent.futures threads produce the wrong output with Python 3.6.

The attached program with Python 3.5.X outputs:
MainThread From main thread
Thread-1 From worker thread

But with 3.6, it outputs:
MainThread From main thread
<concurrent.futures.thread.ThreadPoolExecutor object at 0x7f96711ac278>_0 From worker thread

The bug seem to have been introduced by https://hg.python.org/cpython/rev/1002a1bdc5b1

Here is a patch that restores the previous behavior and update test to catch bogus naming.

Thoughts anyone?

This is a minor bug, but for a common use case (easy to hit), and the fix is trivial.

Ping

I don't think this is a regression, bug, bogos naming.

I agree that "<concurrent.futures.thread.ThreadPoolExecutor object at 0x7f96711ac278>_0" is ugly.
But the name describes what is the thread, than "Thread-1".

How about giving default thread_name_prefix less ugly?
e.g. "ThreadPoolExecutor-worker".

I don't think using repr(self) as a fallback was intentional, that is why I wrote regression, but I may be wrong.

I agree that the previous default 'Thread-x' gives little information, but only the user can give a relevant name to describe what a thread is doing.
Using a new default like "ThreadPoolExecutor-worker_x" would give more information but at the same time it leaks internal information about how the thread was created in the code (which is not relevant when using the logging module), not about what it's doing.

Anyway as long as that repr string is replaced, I am happy :)

OK. I'll wait for another opinions.

Ping, so that this has a chance for the 3.6.1 release.

Ping.

I think any change, included Inada Naoki's idea above is better that the current behavior that pollutes the logging module output.

Unfortunately I cannot rely on the 3.6 new thread_name_prefix argument for portability reasons, and have to manually patch my Python 3.6.x installs just to fix this.

agreed the repr(self) name being surfaced is a regression even if technically "correct".

your patch makes sense, but i think a nicer variant of it will be to name the thread ("Executor_" + str(num_threads)) when no thread_name_prefix is supplied.

Thank you Gregory for the insight and new patch.

Can this be merged in the 3.6 branch as well (targeting the 3.6.3 release)?

New changeset a3d91b43c2851312fb942f31afa12f5961706db6 by Gregory P. Smith in branch 'master':
bpo-29212: Fix the ugly repr() ThreadPoolExecutor thread name. (#2315)
https://github.com/python/cpython/commit/a3d91b43c2851312fb942f31afa12f5961706db6

Yes, I'll get this into 3.6.  The default repr based name was clearly a regression from reasonable behavior.

Gregory, please don't forget to backport the fix in the 3.6 branch, so that it is released with Python 3.6.3.

Thank you

New changeset 7d8282d25d4900dd3367daf28bb393be7f276729 by Gregory P. Smith in branch '3.6':
[3.6] bpo-29212: Fix the ugly repr() ThreadPoolExecutor thread name. (GH-2315) (#3276)
https://github.com/python/cpython/commit/7d8282d25d4900dd3367daf28bb393be7f276729