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.
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6Possible duplicate of Logging uncaught exceptions in PythonTrevor Boyd Smith– Trevor Boyd Smith2017-04-06 18:27:08 +00:00Commented Apr 6, 2017 at 18:27
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3 Answers
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()
7 Comments
NG_
Isn't that good idea to append
sys.__excepthook__(type, value, tb) to your my_handler, so it can process default actions on exception?
bioslime
@Ferdinand Beyer: Neat. Having
logger.exception("Uncaught exception: {0}: {1}".format(str(value.__class__.__name__), str(value))) gives in my case ERROR - Uncaught exception: IndexError: list index out of range and prints for some reason None. How do i also get the full traceback? tb seems to be a traceback object but traceback.print_tb(tb) also just spits out None.
j08lue
@bioslime see this recipe which relies on the
exc_info kwarg to log the traceback, too. It seems to only work with logger.error or logger.critical, but not with logger.exception.
cclauss
The above code does not work for me. Replacing
main() with hello ==== "Hello" still results in a stack trace being printed to the console.
Zhou Hongbo
I prefer this answer too：stackoverflow.com/a/16993115/512111
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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")
1/0
Comments
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
1 Comment
JeffCharter
this will log and then proceed as normal.