Demonstration of setting log level in a handler overrides setting log level in a logger

logger_handler_demo.py

# Demonstrates that setting the log level in a handler overrides any setting of log level in the logger
#
# The purpose of this is to support adding handlers that take extra action or route log messages to other 
# destinations for any logs at higher levels. For instance, creating and adding a handler to the root
# logger where the handler's level is set to ERROR, and streams its logs to a notification service queue.
# Even if the logger's level is set to a lower level of logging, the specialized handler only routes
# ERROR or higher log messages to the notification service.
#
# The problem arises if the handler that is set to a particular log level is the root logger's sole
# stdout handler. In this case, it becomes difficult to change the log level on the logger, because the
# level set on its handler takes precedence.
#

import sys
import logging

# set up root logger as if running logging.basicConfig()
root_log = logging.getLogger()
root_handler = logging.StreamHandler(sys.stdout)
root_handler.setFormatter(
    logging.Formatter(
        fmt='%(asctime)s.%(msecs)03d %(levelname)s [%(name)s] %(message)s',
        datefmt='%Y-%m-%d %H:%M:%S'
    )
)
root_log.addHandler(root_handler)

# uncomment this line to see that the handler level overrides setting the logger level
# root_handler.setLevel(logging.ERROR)
root_log.setLevel(logging.DEBUG)

log = logging.getLogger(__name__)
log.setLevel(logging.DEBUG)

log.info("log message")


sublog = logging.getLogger(__name__ + ".sub")
# sublog.info("sublog message")
# sublog = LA(sublog)
sublog.info("sublog message")
sublog.info("sublog message")

other_log = logging.getLogger("other")
other_log.setLevel(logging.DEBUG)
other_log.info("other_log message")
other_log.info("other_log message")