How to test threading in python

Question

I am learning how to test threads in Python as I have never done it before. I have put a lock in but it says that I have an assertion error which is fine. I am wondering if the following code is correct

import threading

i = 0

def test():
    global i
    for _ in range(100000):
        with threading.Lock():
            i += 1

threads = [threading.Thread(target=test) for t in range(10)]
for t in threads:
    t.start()

for t in threads:
    t.join()

assert i == 1000000, i

Answer 1

Your problem is that you create a new Lock on every iteration, which is always unlocked.

This way it'll work, because your Threads will try to aquire the same lock.

import threading

i = 0

lock = threading.Lock()

def test():
    global i
    for _ in range(100000):
        with lock:
            i += 1

threads = [threading.Thread(target=test) for t in range(10)]
for t in threads:
    t.start()

for t in threads:
    t.join()

print(i)