There's a special log level called NOTSET. A logger with NOTSET inherits the level of its first ancestor that has a level set explicitly. This allows you to define a default behavior for child loggers without explicitly setting their levels.

The LogRecord eventually reaches the root logger. If the root logger has a level set (anything but NOTSET), it acts as the final gatekeeper, filtering messages based on its level. If the root logger has a NOTSET level, all messages are propagated to its handlers."

We can get the root by not providing a name.

import logging

root_logger = logging.getLogger()

By default, the root logger has WARNING as log level. So, warning logs will be printed, but anything below that won’t. We can downgrade the root logger to DEBUG to see all logs.

root_logger.setLevel(logging.DEBUG)

logger = logging.getLogger("child")
logger.debug("This is a debug message")

This will output:

$ python my_app.py
This is a debug message