Ref-strings in logging messages (was: Performance issue with CPython 3.10 + Cython)

[Barry]

> On 7 Oct 2022, at 19:09, Weatherby,Gerard <gweatherby at uchc.edu> wrote:
> The obvious way to avoid log generation is:
> 
> if logger.isEnableFor(logging.DEBUG):
>                logger.debug( expensive processing )
> 
> 
> Of course, having logging alter program flow could lead to hard to debug bugs.

Altered flow is less of an issue the the verbosity of the above.
We discussed ways to improve this pattern a few years ago.
That lead to no changes.

What I have used is a class that defines __bool__ to report if logging is enabled and __call__ to log. Then you can do this:

log_debug = logger_from(DEBUG)

log_debug and log_debug(‘expensive %s’ % (complex(),))

Barry

> 
> From: Python-list <python-list-bounces+gweatherby=uchc.edu at python.org> on behalf of Barry <barry at barrys-emacs.org>
> Date: Friday, October 7, 2022 at 1:30 PM
> To: MRAB <python at mrabarnett.plus.com>
> Cc: python-list at python.org <python-list at python.org>
> Subject: Re: Ref-strings in logging messages (was: Performance issue with CPython 3.10 + Cython)
> *** Attention: This is an external email. Use caution responding, opening attachments or clicking on links. ***
> 
>> On 7 Oct 2022, at 18:16, MRAB <python at mrabarnett.plus.com> wrote:
>> 
>> On 2022-10-07 16:45, Skip Montanaro wrote:
>>>> On Fri, Oct 7, 2022 at 9:42 AM Andreas Ames <andreas.0815.qwertz at gmail.com>
>>>> wrote:
>>>> 1. The culprit was me. As lazy as I am, I have used f-strings all over the
>>>> place in calls to `logging.logger.debug()` and friends, evaluating all
>>>> arguments regardless of whether the logger was enabled or not.
>>> I thought there was some discussion about whether and how to efficiently
>>> admit f-strings to the logging package. I'm guessing that's not gone
>>> anywhere (yet).
>> Letting you pass in a callable to call might help because that you could use lambda.
> 
> Yep, that’s the obvious way to avoid expensive log data generation.
> Would need logging module to support that use case.
> 
> Barry
> 
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