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

Barry Warsaw barry at python.org
Wed Sep 30 20:27:59 CEST 2009

On Sep 30, 2009, at 1:01 PM, Antoine Pitrou wrote:

Why not allow logging.Formatter to take a callable, which would in turn call the callable with keyword arguments?

Therefore, you could write: logging.Formatter("{asctime} - {name} - {level} - {msg}".format)

This is a very interesting idea.

Note that one of the reasons to /at least/ support {}-strings also is
that %-strings are simply too error prone in many situations. For
example, if I decide to support internationalization of log format
strings, and all I can use is %-strings, it's almost guaranteed that I
will have bugs because a translator forgot the trailing 's'. This
exactly the motivation that led to PEP 292 $-strings.

In fact, while we're at it, it would be kind of cool if I could use $- strings in log templates. Antoine's idea of accepting a callable
might fit that bill nicely.

-Barry

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