Python logging: my logger.info()/logger.debug() messages don't show up, or logging.basicConfig() seems to do nothing. How do I configure logging correctly?

Cause: by default the root logger's level is WARNING, so info and debug messages are dropped unless you lower the level. logging.basicConfig() only configures the root logger if it has no handlers yet; if anything logged earlier, or a library or framework (Jupyter, some test runners, web frameworks) already added a handler, a later basicConfig call is silently ignored. Setting a level on a logger isn't enough if its handlers have a higher level, and messages from a named logger propagate to the root logger's handlers. Fix: 1. Configure logging once, at program start, before importing code that logs: logging.basicConfig(level=logging.INFO, format='%(asctime)s %(levelname)s %(name)s: %(message)s'). 2. If something configured logging first and you want your settings anyway, use logging.basicConfig(..., force=True) (Python 3.8+), which removes existing root handlers before applying yours. 3. In library code, don't call basicConfig: create a module logger with logger = logging.getLogger(__name__) and leave configuration to the application (the logging HOWTO recommends libraries add only a NullHandler). 4. Check both levels: the logger's level (logger.setLevel) and each handler's level; the stricter one wins. To quiet a noisy dependency, set its logger's level: logging.getLogger('urllib3').setLevel(logging.WARNING). 5. For larger apps, configure with logging.config.dictConfig in one place. 6. If you see every message twice, you added a handler to a named logger and it also propagates to the root handler; set logger.propagate = False or add the handler only to root. Verify: logging.getLogger().getEffectiveLevel() returns the level you expect, and a test logger.info('hello') appears once in the output. Sources: https://docs.python.org/3/howto/logging.html https://docs.python.org/3/library/logging.html