Better to raise an error directly or from within a logger

Question

Which of the following two methods of raising an error is preferred?

def _fetch_data(self):
    if self.from_cache:
        logger.debug('Trying to load local file %s...' % self.fp)
        # Grab the data from a local file
        if not os.path.exists(self.fp):

            # first way -- from logger
            logger.error('ERROR: Local file {self.fp} does not exist')

            # second way -- directly raising
            raise SystemExit(f"ERROR: Local file {self.fp} does not exist")

Why is one approach preferred over the other?

Answer 1

One of them prints and takes no action (implying the issue is non-fatal), the other actually attempts to terminate the program (though the idiomatic approach in this case would just be sys.exit(f"ERROR: Local file {self.fp} does not exist") ; it's equivalent to the raise , but slightly clearer in intent).

Choose the one that makes sense in context; if the file is necessary to continue operation, raise an exception (log first if you like), if it's non-fatal with a reasonable way of continuing operation, you can just log.

Note that SystemExit implies it's really fatal (people shouldn't be trying to catch that typically). Often, it's better to raise some other, more descriptive, less "implies definitely fatal" exception in case the caller knows a good way to handle the problem.