Python thread doesn't change global variable inside a function

Question

The most basic form of something I want to code is the code as follows:

import threading

arr = []
def test(id):
    global arr
    arr.append(id)

threading.Thread(target=test, args="8")
print(arr)

What I want to do is to append "8" to a global variable called arr But this doesn't happen, and print(arr) gives this output:

[]

However, if I use this code, everything works fine:

import threading

arr = []
def test(id):
    global arr
    arr.append(id)

test("8")
print(arr)

The problem seems to be with thread, so how can I use thread and also change the value of a global variable inside the function test ?

Answer 1

You also have to start the thread to actually run the function test

import threading

arr = []
def test(id):
    global arr
    arr.append(id)

t = threading.Thread(target=test, args="8")
t.start()
t.join()
print(arr)