> On 8 Oct 2022, at 11:50, Weatherby,Gerard <[email protected]> wrote:
>
> Logging does support passing a callable, if indirectly. It only calls __str__
> on the object passed if debugging is enabled.
>
> class Defer:
>
> def __init__(self,fn):
> self.fn = fn
>
> def __str__(self):
> return self.fn()
>
> def some_expensive_function():
> return "hello"
>
> logging.basicConfig()
> logging.debug(Defer(some_expensive_function))
Oh what a clever hack. Took a few minutes of code reading to see why this works.
You are exploiting the str(msg) that is in class LogRecords getMessage().
```
def getMessage(self):
"""
Return the message for this LogRecord.
Return the message for this LogRecord after merging any user-supplied
arguments with the message.
"""
msg = str(self.msg)
if self.args:
msg = msg % self.args
return msg
```
Barry
>
>
> From: Python-list <[email protected]
> <mailto:[email protected]>> on behalf of
> Barry <[email protected] <mailto:[email protected]>>
> Date: Friday, October 7, 2022 at 1:30 PM
> To: MRAB <[email protected] <mailto:[email protected]>>
> Cc: [email protected] <mailto:[email protected]>
> <[email protected] <mailto:[email protected]>>
> 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 <[email protected]> wrote:
> >
> > On 2022-10-07 16:45, Skip Montanaro wrote:
> >>> On Fri, Oct 7, 2022 at 9:42 AM Andreas Ames
> >>> <[email protected]>
> >>> 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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