Using python's logging module to log all exceptions and errors

Question

I want to check for errors in a particular background file, but the standard error stream is being controlled by the program in the foreground and the errors in the file in the question are not being displayed. I can use the logging module and write output to a file, though. I was wondering how I can use this to log all exceptions, errors and their tracebacks.

Answer 1

It's probably a bad idea to log any exception thrown within the program, since Python uses exceptions also for normal control flow.

Therefore you should only log uncaught exceptions. You can easily do this using a logger's exception() method , once you have an exception object.

To handle all uncaught exceptions, you can either wrap your script's entry point in a try...except block, or by installing a custom exception handler by re-assigning sys.excepthook() :

import logging
import sys

logger = logging.getLogger('mylogger')
# Configure logger to write to a file...

def my_handler(type, value, tb):
    logger.exception("Uncaught exception: {0}".format(str(value)))

# Install exception handler
sys.excepthook = my_handler

# Run your main script here:
if __name__ == '__main__':
    main()

Answer 2

import sys
import logging
import traceback

# log uncaught exceptions
def log_exceptions(type, value, tb):
    for line in traceback.TracebackException(type, value, tb).format(chain=True):
        logging.exception(line)
    logging.exception(value)

    sys.__excepthook__(type, value, tb) # calls default excepthook

sys.excepthook = log_exceptions

Answer 3

Inspired of the main answer + How to write to a file, using the logging Python module? + Print original exception in excepthook , here is how to write the full traceback into a file test.log , like it would be printed in the console:

import logging, sys, traceback
logger = logging.getLogger('logger')
fh = logging.FileHandler('test.log')
logger.addHandler(fh)
def exc_handler(exctype, value, tb):
    logger.exception(''.join(traceback.format_exception(exctype, value, tb)))
sys.excepthook = exc_handler
print("hello")
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