Python logging: different behavior between using f

Question

I just discovered a different behavior of Python logging, depending on if I use logging with fileconfig and logging with programmatic config.

To demonstrate, I created two minimal examples.

In the first example I'm configuring logging programmatically. This example works as expected - the debug log message is printed to the console.

# foo.py
import logging

logger = logging.getLogger(__name__)

class Foo(object):
    def __init__(self):
        logger.debug('debug log from Foo')

##########################################################################
# loggingtest.py
import logging.config

from foo import Foo

if __name__ == '__main__':
    consoleLogger = logging.StreamHandler()
    formatter = logging.Formatter(
        '%(asctime)-6s: %(name)s - %(levelname)s - %(message)s')
    consoleLogger = logging.StreamHandler()
    consoleLogger.setLevel(logging.DEBUG)
    consoleLogger.setFormatter(formatter)

    rootLogger = logging.getLogger() 
    rootLogger.addHandler(consoleLogger)
    rootLogger.setLevel(logging.NOTSET)
    # prints debug log message to console
    foo = Foo()

In my second example, I'm configuring logging with fileConfig. As far as I can see, the log-config-file should have the exact same behavior. But still, the debug log message is NOT printed in this example.

# foo.py (same as above)
import logging

logger = logging.getLogger(__name__)

class Foo(object):
    def __init__(self):
        logger.debug('debug log from Foo')
##########################################################################
# loggingtest.py
import logging.config

from foo import Foo

if __name__ == '__main__':
    logging.config.fileConfig('logging.cfg')    

    # does NOT print debug log message to console. WHY???
    foo = Foo()

##########################################################################
# logging.cfg
[loggers]
keys = root

[logger_root]
level = NOTSET
handlers = consoleHandler

[formatters]
keys = complex

[formatter_complex]
format = %(asctime)s - %(name)s - %(levelname)s - %(module)s : %(lineno)d - %(message)s

[handlers]
keys = consoleHandler

[handler_consoleHandler]
class=StreamHandler
level=DEBUG
formatter=complex
args=(sys.stdout,)

So why is the second example using a logging fileconfig NOT printing my debug log message to the console?

Answer 1

Since fileConfig disables existing loggers by default, call

logging.config.fileConfig("logging.cfg")

before

from foo import Foo

or call

logging.config.fileConfig("logging.cfg",disable_existing_loggers=0)