[Python-Dev] New-style formatting in the logging module (was Re: cpython (3.2): Issue #14123: Explicitly mention that old style % string formatting has caveats)

[Nick Coghlan]

On Mon, Feb 27, 2012 at 10:44 AM, Larry Hastings <larry at hastings.org> wrote:
> On 02/26/2012 03:33 PM, Guido van Rossum wrote:
>>
>> One thing I'd like to see happening regardless is support for
>> new-style formatting in the logging module. It's a little tricky to
>> think how that would work, alas -- should this be a property of the
>> logger or of the call?
>
>
> There already is some support.  logging.Formatter objects can be initialized
> with a "style" parameter, making this a property of the logger.  (New in
> 3.2.)
>
>   http://docs.python.org/py3k/library/logging.html#formatter-objects
>
> Is that what you had in mind?

It's half the puzzle (since composing the event fields into the actual
log output is a logger action, you know the style when you supply the
format string). The other half is that logging's lazy formatting
currently only supporting printf-style format strings - to use brace
formatting you currently have to preformat the messages, so you incur
the formatting cost even if the message gets filtered out by the
logging configuration. For that, a logger setting doesn't work, since
one logger may be shared amongst multiple modules, some of which may
use printf formatting, others brace formatting.

It could possibly be a flag to getLogger() though - provide a facade
on the existing logger type that sets an additional event property to
specify the lazy formatting style.

Cheers,
Nick.

-- 
Nick Coghlan   |   ncoghlan at gmail.com   |   Brisbane, Australia