Python Logging: Output not formatted as expected

I am having some issues with the output of my Python logs.

Here is how I am initiating it:

import logging

def get_logger():

    logger = logging.getLogger(__name__)
    logger.setLevel(logging.DEBUG)

    handler = logging.StreamHandler()
    formatter = logging.Formatter("%(levelname)s - %(message)s")

    handler.setFormatter(formatter)

    if not logger.hasHandlers():
        logger.addHandler(handler)

    return logger

I have a function here which should provide a log entry when it is called

def app():
    logger = get_logger()
    logger.debug("Page 1 Initiated")

In my main file I have this:

if __name__ == '__main__':
    logger = get_logger()
    logger.debug("Started")
    run_ui()

run_ui() will call app()

Here is my issue: When I run main.py I will get the following log output in my console

2023-04-03 15:15:24.354 DEBUG   src.logging_config: Started
2023-04-03 15:15:26.509 Page 1 Initiated

It seems like my formatter is not working properly? I have it set so that I get level name, followed by the message. But I just keep getting that second line of output every time. Based on my formatter, I am expecting to get this:

DEBUG Page 1 Initiated

Am I missing something here?

You are attaching your handlers to child loggers of the logger hierarchy:

logger = logging.getLogger(__name__)

Child loggers are useful when you want to print the name of the logger (i.e. see the package where the logger was called, filter logs based on packages etc.). However, if you want to format messages, usually the handlers are attached to the root logger, like this:

if not logging.getLogger().hasHandlers():
    handler = logging.StreamHandler()
    formatter = logging.Formatter("%(levelname)s - %(message)s")
    handler.setFormatter(formatter)
    logging.getLogger().addHandler(handler)

It is still best to use the child logger when logging, those logs are propagated to the root logger automatically.

See: Python logging hierarchy