[Python-Dev] summary of transitioning from % to {} formatting (original) (raw)

Vinay Sajip vinay_sajip at yahoo.co.uk
Mon Oct 5 23:46:52 CEST 2009

Nick Coghlan <ncoghlan gmail.com> writes:

Oh, I see what you meant now - you were pointing out that lazy formatting APIs (such as logging) already don't work properly for alternative formatting mechanisms (such as string.Template).

Logging doesn't work automatically with string.Template as it pre-dates string.Template, but it can be made to work without too much trouble:

(a) Subclass Formatter to use $-formatting instead of %-formatting for e.g. the lines written to log files, and (b) Use a class like DollarMessage which I mentioned elsewhere in this thread, to format logging call format strings and arguments.

Both of these approaches will also work for {}-formatting. The present thread really started out with a view to suggesting that the stdlib start adopting {}-format as "native", rather than %-format.

Would it be helpful if I added a section to the Python docs about how to use alternative formatting systems with logging?

Regards,

Vinay Sajip

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