Python sys.excepthook on multiprocess

Question

I am trying to set custom sys.excepthook on multiprocess. but it does not work.

In below code, I have expected that to print This is my traceback function: string as a prefix of error message, but it doesn't.

code:

from multiprocessing import Process
import time
import traceback
import logging
import sys

def excepthook(etype, evalue, traceback):
    traceback_strs = traceback.format_exception_only(etype, evalue)
    exception_str = "This is my traceback function:" + "\r\n".join(traceback_strs)
    print("ExceptHook")
    print(exception_str)


def subprocess_main():
    sys.excepthook = excepthook
    time.sleep(3)
    raise Exception("HelloWorld")


if __name__ == "__main__":
    p = Process(target=subprocess_main)
    p.start()
    p.join()

Why it does not work?

OS:Windows10
Python: 3.6.3

Answer 1

sys.excepthook is called when there is an uncaught exception, but Process has exception handler routine , which consumed the exception before your hook.

If you still want custom exception handling, you may overriden Process.run method:

class MyProcess(Process):

    def run(self):
        try:
            super().run()
        except Exception:
            excepthook(*sys.exc_info())

ps: argument traceback of your original function excepthook shadowed module object traceback , which will trigger an error if it actually being called.