What is the purpose of a mutex when working with threads in Python?

A mutex (mutual exclusion) in Python is used for thread synchronization and to prevent concurrent access to shared resources. It ensures that at any given moment, only one thread can execute the critical section of code protected by this mutex.

This is important to avoid race conditions, where multiple threads modify the same data simultaneously, which can lead to unpredictable results.

An example of using a mutex with the threading module:

import threading

lock = threading.Lock()
shared_resource = 0

def increment():
    global shared_resource
    with lock:  # Acquire the mutex
        temp = shared_resource
        temp += 1
        shared_resource = temp

threads = [threading.Thread(target=increment) for _ in range(1000)]
for t in threads:
    t.start()
for t in threads:
    t.join()

print(shared_resource)  # Expected to be 1000

Without a mutex, the result could be less than 1000 due to concurrent access.