How to implement logging for an imported module?

[Robert Latest]

Hello,

I'm trying to add logging to a module that gets imported by another module. But
I only get it to work right if the imported module knows the name of the
importing module. The example given in the "Logging Cookbook" also rely on this
fact.

https://docs.python.org/3/howto/logging-cookbook.html#logging-cookbook

I couldn't find any information on how to implement logging in a library that
doesn't know the name of the application that uses it. How is that done?

Here's some example code consisting of the main module foo.py and imported
modules bar.py and baz.py


### foo.py
import logging

import bar, baz

formatter = logging.Formatter(
    '%(asctime)s - %(name)s - %(levelname)s - %(message)s')

ch = logging.StreamHandler()
ch.setFormatter(formatter)

logger = logging.getLogger('foo')
logger.addHandler(ch)
logger.setLevel(logging.DEBUG)

logger.debug('debug from <%s>', __name__)
logger.info('info from <%s>', __name__)
logger.warning('warning from <%s>', __name__)
logger.error('error from <%s>', __name__)

bar.func()
baz.func()

### bar.py
'''This "generic" approach doesn't honor loglevel or formats
when imported by another module'''
import logging

l = logging.getLogger(__name__)
def func():
    l.debug('debug from <%s>', __name__)
    l.info('info from <%s>', __name__)
    l.warning('warning from <%s>', __name__)
    l.error('error from <%s>', __name__)

### baz.py
'''This only works if the importing module is named 'foo', which
precludes its use as a library module'''
import logging

l = logging.getLogger('foo.baz')
def func():
    l.debug('debug from <%s>', __name__)
    l.info('info from <%s>', __name__)
    l.warning('warning from <%s>', __name__)
    l.error('error from <%s>', __name__)