Handling exceptions in threads python

Threads are independent tasks that run concurrently and unhandled exceptions in threads can lead to unexpected behavior and a crash of the application.

The default behaviour of exceptions in a thread is different when compared to the exceptions in the main thread.

By default, when an exception occurs in a thread, it doesn’t propagate to the main thread. Instead, the exception is raised within the thread context, and if it’s not handled properly, the thread will terminate without any intimation.

Catch exceptions within the threads

The simplest way to handle exceptions in threads is to catch them within the thread’s execution function. We can keep the code inside a try-except block and handle the exception accordingly. If any exception comes in the try block, the except block will be executed and the exception can be handled here.

Following is the example

import threading

def thread_function():
    try:
        # Your thread code here
        pass
    except Exception as e:
        print("Exception in thread:", e)

thread = threading.Thread(target=thread_function)
thread.start()

Propate the exceptions to the main thread

Some times we may need to propagate the exceptions to main thread such that the main thread will take descision based on the descision. To propagate exceptions from threads to the main thread, we can use the threading.excepthook function. This function allows us to set a global exception handler for all threads.

import threading

def exception_handler(args):
    print("Exception in thread:", args)

threading.excepthook = exception_handler

def thread_function():
    # Your thread code here
    pass

thread = threading.Thread(target=thread_function)
thread.start()

In the above example, any unhandled exception raised in the thread will be caught by the exception_handler function and printed.