Python Gotcha: Logging an uncaught exception
Python Gotcha: Logging an uncaught exception
July 17, 2025
I would be try/except blocks throughout my code but I would have a large try/except block to catch any uncaught exception. Andrew’s article did a good job showing me another way.
The solution is sys.excepthook. This is called when any exception is raised and uncaught, except for SystemExit. It’s pretty easy to utilize as well. A few small changes to the above code will allow us to log this completely unexpected ZeroDivisionError.
import logging
import sys
logger = logging.getLogger(__name__)
logger.setLevel(logging.INFO)
handler = logging.FileHandler("app.log")
formatter = logging.Formatter("%(asctime)s %(name)s %(levelname)s %(message)s")
handler.setFormatter(formatter)
logger.addHandler(handler)
def handle_uncaught_exception(exc_type, exc_value, exc_traceback):
logger.critical(
"uncaught exception, application will terminate.",
exc_info=(exc_type, exc_value, exc_traceback),
)
sys.excepthook = handle_uncaught_exception
def divide(a, b):
return a/b
def main():
logger.info("Application start")
a = 10
b = 0
logger.info(divide(a,b))
logger.info("Application end")
if __name__ == "__main__":
main()The important bit is the new handle_uncaught_exception function and the
sys.excepthook line (with appropriate import statement).
What I would do with my code, especially the ones where I log using my log_to_db library, I will save to a database:
...
def handle_uncaught_exception(exc_type, exc_value, exc_traceback):
tb = traceback.extract_tb(exc_traceback)
error_filename, lineno, funcname, code_error = tb1[-1]
db_logger.critical(
message="Uncaught exception, will terminate.",
details=dict(
error_type=str(exc_type),
error_value=str(exc_value),
error_line_number=str(lineno),
error_filename=str(error_filename),
error_function=str(funcname),
code_error=str(code_error),
)
sys.excepthook = handle_uncaught_exception
...