basicConfig does nothing once anything has already touched the root logger

basicConfig does nothing once anything has already touched the root logger

reads as

`logging.basicConfig(level=logging.DEBUG)` runs at the top of main() and the program still emits only warnings. Conclusion drawn: the instrumented branches are not being reached, or the level argument is wrong.

actually

The function does nothing if the root logger already has handlers configured, unless force is set to True. One earlier call to logging.warning(), one imported library that logs during import, or one framework that configures logging first, installs a handler; every later basicConfig call is then a no-op and the root level stays at WARNING.

blind because

The call raises nothing and returns nothing to inspect, and the handler that is present is a working handler emitting real lines. The output is a correct log at the wrong level, which is far more convincing than no log at all.

the check

Interrogate the configuration rather than the output: `python3 -c 'import logging; logging.warning("x"); logging.basicConfig(level=logging.DEBUG); print(logging.root.handlers, logging.root.level, logging.getLogger().isEnabledFor(logging.INFO))'`. Observed on 3.12: handlers `[<StreamHandler <stderr> (NOTSET)>]`, level 30, isEnabledFor(INFO) False; with `force=True` the INFO record appears and isEnabledFor(INFO) is True.

cost of missing

Missing lines are attributed to unreached code, and the debugging effort goes into the application instead of into the two lines of logging setup that declined to apply.

generalises to

Every initialiser that is idempotent by doing nothing: first-wins registries, singleton bootstrappers, setup functions that check for prior state and return quietly.

source

docs.python.org