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The threading module uses an hack to log actions to help debugging. The log depends on 3 flags: __debug__, threading._VERBOSE and a verbose attribute (each threading class has such attribute). By default, _note() is always called but does nothing: it checks the verbose attribute and return if the flag is False.
Attached threading_note.patch only calls _note() if verbose is True to avoid a Python function call (which is slow in CPython). It avoids also a _Verbose parent class and pass the verbose flag to subobjects (e.g. Semaphore sets verbose argument of its Condition object).
I don't think that it is really useful to be able to enable/disable logs on only one threading object, so it is maybe simpler to have only one global flag (instead of 3 flags): threading._VERBOSE. Attached threading_note_global.patch replaces _note() method by a function, remove _Verbose class and the _verbose attribute, and only call _note() if _VERBOSE is True.
_VERBOSE and verbose arguments are undocumented and not tested, so I hope nobody relies on their API ;-)

(threading_note_global.patch was completly wrong, here is the fixed version)

Tim, do you happen to know what the goal was with the threading._VERBOSE hack and the undocumented _Verbose class?

On #13550 I asked Guido about the Thing/_Thing function/class indirection and use of _Verbose; the reply:
> IIRC:
> 
> The design started out this way because it predates new-style classes. When this was put in one
> couldn't subclass extension types, and there were plans/hopes to replace some of the lock types
> with platform-specific built-in versions on some platforms.
>
> Since it is now possible to write subclassable extension types the Thing/_Thing design is no
> longer needed.
> 
> I'm not sure about the _Verbose hacks, if it is deemed not useful I'm fine with letting it go.

I'm personally +1 on removing the verbose thing altogether:
- it's ugly
- I doubt it's really useful (I mean, printing to stderr - which is often line buffered or unbuffered - upon every action will probably change the timing)
- it also brings some problems on its own, e.g. #4188
So unless there's a good reason behind it, I think we could let it go.

Alright, Nick agreed on python-dev to remove the logging hack.

haypo’s threading_note_global looks good to me. The only thing I’m not sure about is the signature change from X(verbose, *args, **kwargs) to X(*args, **kwargs): is it okay?
(BTW you probably want to delete the obsolete reference to ihooks in a comment before committing.)

> Alright, Nick agreed on python-dev to remove the logging hack.
You mean removing complelty debug logging from the threading module? Or just to simplify the code to decide if we should log or not?

I believe Charles-François was referring to this message:
http://mail.python.org/pipermail/python-dev/2012-January/115372.html
We shouldn't be encumbering threading *all the time* with stuff that "might be useful sometimes". Adding selective output to help debug problems can be handled with Thread subclasses, or even temporarily running with a modified threading.py (for people hacking on the stdlib itself).

New changeset 8ec51b2e57c2 by Victor Stinner in branch 'default':
Close #13550: Remove the debug machinery from the threading module: remove
http://hg.python.org/cpython/rev/8ec51b2e57c2