Python logger does not print debug messages, even if logger.getEffectiveLevel() is DEBUG [duplicate]

Question

The following code changes the log level from INFO to DEBUG, and even though logger.getEffectiveLevel() returns DEBUG, the debug message doesn't get logged, as the output shows.

version of python: 3.10.12

---out.log---

log level 1: INFO
log level 2: DEBUG

Code

import logging
import logging.config

def test_change_log_level():
    logger = logging.Logger("my-logger", logging.INFO)
    file_handler = logging.FileHandler(filename="out.log")

    file_handler.setLevel(logging.INFO)
    logger.addHandler(file_handler)

    logger.debug("should not be logged ...")
    logger.info("log level 1: %s", logging.getLevelName(logger.getEffectiveLevel()))

    logger.setLevel(logging.DEBUG)
    file_handler.setLevel(logging.DEBUG)

    logger.info("log level 2: %s", logging.getLevelName(logger.getEffectiveLevel()))
    logger.debug("debug level is effective")


if __name__ == '__main__':

    test_change_log_level()

wjandrea · Accepted Answer · 2024-02-01 18:42:16Z

1

From the docs:

Loggers should NEVER be instantiated directly, but always through the module-level function logging.getLogger(name).

Secondly, the handler is not relevant to the problem, so here I've replaced it with a root handler.

import logging
logging.basicConfig(format='')

def test_change_log_level():
    logger = logging.getLogger("my-logger")
    logger.setLevel(logging.INFO)

    logger.debug("should not be logged ...")

    logger.setLevel(logging.DEBUG)

    logger.debug("debug level is effective")

if __name__ == '__main__':
    test_change_log_level()

Output:

debug level is effective

answered Feb 1, 2024 at 18:42

wjandrea

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1 Comment

wjandrea Over a year ago

P.S. Check out How to Ask for tips for future questions, like starting with your own research (namely, reading the docs yourself), and making a minimal reproducible example (namely, removing the handler, but also playing around with your code until you localize the problem to, ideally, a single line).

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