Question

Could you help me solve the following incompatibility issue between Python 2.5 and 2.6?

logger.conf:

[loggers]
keys=root,aLogger,bLogger

[handlers]
keys=consoleHandler

[formatters]
keys=

[logger_root]
level=NOTSET
handlers=consoleHandler

[logger_aLogger]
level=DEBUG
handlers=consoleHandler
propagate=0
qualname=a

[logger_bLogger]
level=INFO
handlers=consoleHandler
propagate=0
qualname=b

[handler_consoleHandler]
class=StreamHandler
args=(sys.stderr,)

module_one.py:

import logging
import logging.config

logging.config.fileConfig('logger.conf')
a_log = logging.getLogger('a.submod')
b_log = logging.getLogger('b.submod')

def function_one():
    b_log.info("function_one() called.")

module_two.py:

import logging
import logging.config

logging.config.fileConfig('logger.conf')
a_log = logging.getLogger('a.submod')
b_log = logging.getLogger('b.submod')

def function_two():
    a_log.info("function_two() called.")

logger.py:

from module_one import function_one
from module_two import function_two

function_one()
function_two()

Output of calling logger.py under Ubuntu 9.04:

$ python2.5 logger.py
$

$ python2.6 logger.py
function_one() called.
function_two() called.
$

Answer 1

This is a bug which was fixed between 2.5 and 2.6. The fileConfig() function is intended for one-off configuration and so should not be called more than once – however you choose to arrange this. The intended behaviour of fileConfig is to disable any loggers which are not explicitly mentioned in the configuration, and leave enabled the mentioned loggers and their children; the bug was causing the children to be disabled when they shouldn’t have been. The example logger configuration mentions loggers ‘a’ and ‘b’; after calling getLogger(‘a.submod’) a child logger is created. The second fileConfig call wrongly disables this in Python 2.5 – in Python 2.6 the logger is not disabled as it is a child of a logger explicitly mentioned in the configuration.