How to use logging.getLogger(__name__) in multiple modules

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As pointed out by @shmee in this answer, the logger hierarchy must be defined explicitly in the logger name, using dot-notation. That is, if the logger name in main_module.py is e.g. 'a', then the logger name in auxiliary_module.py must be 'a.b' (not just 'b'), in order for it to inherit the configuration of logger 'a'. This is also mentioned in the getLogger() documentation.

However, this should be taken care of automatically when using __name__, as noted in the logging how-to:

This means that logger names track the package/module hierarchy, and it’s intuitively obvious where events are logged just from the logger name.

The thing is, for this to work, you need to use __name__ in the correct way, and I did not do that.

The problem in my example is in the organization of the files in the cookbook-example package folder:

Both the main module and the auxiliary module are at the same level (i.e. in the same folder). So, as explained here, the __name__ for the main module will then be '__main__' (as it is the top-level script), and the __name__ for the auxiliary module will be 'auxiliary_module' (i.e. the filename), NOT '__main__.auxiliary_module'.

As a result, the logger in the auxiliary module will be a child of the root logger, not a child of the '__main__' logger, and it will thus inherit the root logger configuration (which still has the default logging level WARNING) instead of the configuration specified in the main module.

So, to make the example work, we have several options:

  1. Replace getLogger(__name__) in the main module by getLogger().
    This will apply the config to the root logger and therefore also to
    the auxiliary module logger, as suggested by @shmee.

  2. Replace getLogger(__name__) in the auxiliary module by
    getLogger('__main__.' + __name__). The result will be equivalent
    to the original cookbook-example (except that the main logger is now called
    '__main__' instead of 'spam_application').

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