The excepthook() function of Python threading module

Function Name:

excepthook()

Function Signature:

excepthook(args, /)

Returns:

none

Overview:

The threading.excepthook is an exception handler function with an args parameter.
Exceptions that are not handled by the child threads are handled by the threading.excepthook handler.
In order to handle such unhandled exceptions threading.excepthook has to be overridden with the custom exception handler with an args parameter.

def childThreadHandleAllHook(args):
   print(“====Common handler for all child threads===”):
   print(args.exc_type)
   print(exc_value)
   print(exc_traceback)
   print(thread)
   print(“====”)

threading.excepthook = childThreadHandleAllHook

The threading.excepthook will not handle any exceptions that are not handled by the main thread. To handle the unhandled exceptions of the main thread sys.excepthook has to be overridden.

def mainHandleAllHook(type, value, traceback):
   print(“====Catch all for main thread===”)
   print(type)
   print(value)
   print(traceback)

sys.excepthook = mainHandleAllHook

Example:

# Example Python program that uses a custom exception hook to handle exceptions that are not handled by the child threads
import threading
import sys

# A thread writes one thousand integers to a disk file
# and raises OSError for any failure
# during the writes, which also raises an Exception
# as it exits
def threadFunc1():
   print("Child thread - enter")
   try:
       diskFile = open("1000ints.txt", "w")
       for i in range(0, 1000):
           diskFile.write("{}".format(i))
           if(i < 1000):
               diskFile.write(",")
   except OSError as ose:
       print("Error opening/writing to file")

   print("Child thread - before exit")
   raise Exception("Another odd exception")

# A trivial thread function
def threadFunc2():
raise Exception("From threadFunc2")

# The custom exception handler
def threadExceptionHook(args):
   print("No handlers? I am here...from threadExceptionHook...")
   print("=====Begin child thread exception info:=====")
   print(args.exc_type)
   print(args.exc_value)
   print(args.exc_traceback)
   print(args.thread)
   print("=====End child thread exception info=====")

def mainExceptionHook(type, value, traceback):
   print("From mainExceptionHook:")
   print(type)
   print(value)
   print(traceback)

# Override sys.excepthook
sys.excepthook = mainExceptionHook

# Override threading.excepthook
threading.excepthook = threadExceptionHook

# Create different child threads
childThread1 = threading.Thread(target = threadFunc1)
childThread1.start()
childThread1.join()

childThread2 = threading.Thread(target = threadFunc2)
childThread2.start()
childThread2.join()

# raise exception from main thread
raise Exception("From main")

Output:

Child thread - enter

Child thread - before exit

No handlers? I am here...from threadExceptionHook...

=====Begin child thread exception info:=====

Another odd exception

<Thread(Thread-1 (threadFunc1), started 6180892672)>

=====End child thread exception info=====

No handlers? I am here...from threadExceptionHook...

=====Begin child thread exception info:=====

From threadFunc2

<Thread(Thread-2 (threadFunc2), started 6180892672)>

=====End child thread exception info=====

From mainExceptionHook:

From main