customizing a logging logger

Vinay Sajip vinay_sajip at
Thu Sep 13 14:24:03 CEST 2007

On 12 Sep, 19:17, garyjefferson... at wrote:
> It seems like using something other than a literal string in the
> message is the way to go, since I assume that its __repr__() won't get
> called unless the logger is actually going to log a message for it.
> Is that right?
> Are any of the other methods likely to provide as-good or better
> performance?

You're almost right - it's __str__() rather than __repr__() that gets
called, when str() is called on the msg object passed in the logging
call. The str() call happens in LogRecord.getMessage(), which is
called (indirectly) from a handler's emit() when the message needs to
be formatted.

So - I don't think that the other methods will provide better
performance, as this approach is the simplest and most direct. I
haven't done any tests to confirm this, though :-(

Note that in order to avoid computation of *other* data passed to the
logging call - i.e. other arguments - you should still use the
logger.isXXXEnabled() idiom to avoid unnecessary computation, where
performance is an issue.

Best regards,

Vinay Sajip

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