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[Python-Dev] New-style formatting in the logging module (wasRe: cpython (3.2): Issue #14123: Explicitly mention that oldstyle % string formatting has caveats)
Vinay Sajipvinay_sajip at yahoo.co.uk
Mon Feb 27 10:24:46 CET 2012
Nick Coghlan <ncoghlan <at> gmail.com> writes:> 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.That isn't necessarily true. Lazy formatting can work for {} and $ formattingtypes, not just %-formatting: seehttp://plumberjack.blogspot.com/2010/10/supporting-alternative-formatting.htmlComposing the event fields into the message is done by the LogRecord, whichcalls str() on the object passed as the format string to get the actual formatstring. This allows you to use any of the standard formatting schemes and stilltake advantage of lazy formatting, as outlined in the above post.Although style support for Formatters is new, that's really for merging thelogging event message into the overall log output (with time, severity etc.) -the support for having your own way of formatting the event message has alwaysbeen there, even before str.format :-)The Formatter style functionality is also available for 2.x through a separatelogutils project which I maintain and which contains features which were addedto logging in 3.2 such as QueueHandler/QueueListener:http://pypi.python.org/pypi/logutils/I will add a section in the logging cookbook about support for alternativeformatting styles. I thought I already had, but on inspection, it appears not tobe the case.Regards,Vinay Sajip
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