Two questions about logging

Matthew Pounsett matt.pounsett at
Wed Jan 11 21:19:16 EST 2012

I'm trying to figure out a couple of things with the logging module,
and I'm hoping someone can provide some pointers.  I've read through
the module docs on, the basic and advanced tutorials, and
the cookbook post, but a couple of things still elude me.

First, I'd like to be able to permit users to do more typical log
rotation, based on their OS's log rotation handler, rather than
rotating logs from inside an application.  This is usually handled by
signalling an application with a HUP, whereupon it closes and then re-
opens all of its logs, getting new file handles (and new inodes).  I
don't see anything in the Handler methods (or anywhere else) that
would let me tell a logger object to refresh the file handles on a log
file.  Is there some standard way to deal with this?

Second, I'm trying to get a handle on how libraries are meant to
integrate with the applications that use them.  The naming advice in
the advanced tutorial is to use __name__ to name loggers, and to allow
log messages to pass back up to the using application's logger for
processing, but these two pieces of advice seem contradictory.. since
log messages only pass back up to the root if the loggers are named

> cat
#!/usr/bin/env python

import logging
import bar

logger = logging.getLogger(__name__)
fh = logging.FileHandler('foo.log')
ch = logging.StreamHandler()
logger.warning('from the first')

> cat
#!/usr/bin/env python

import logging

def funct():
	logger = logging.getLogger(__name__)
	logger.warning('from the second')

> ./
from the first
No handlers could be found for logger "bar"

So, given this state of affairs, how is a library author to use
loggers, given that he or she can't know how authors who use the
library will name their logger objects?  In the above example, what
would the author of do to hook up bar's logger with foo's,
without knowing in advance what foo's logger will be named?

Thanks very much for any suggestions, or pointers to documentation
that I've missed.

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