Python global variable on __main__

Question

since multiprocessing need to be put inside __main__ in windows, i found out that my global variable is not passed to my function.

from multiprocessing import Pool, Value

def Proses(lines):
    global xyz
    try:
        print(lines)
        print(xyz)
    except Exception as e:
        print(e)

def counter_handler(args):
    global counter
    counter = args

def Dosomething():
    a = [i for i in range(10)]
    return a


if __name__ == '__main__':
    # i want to share xyz variable
    xyz = Dosomething()

    threads = []
    data = ["bjir", "bjir", "bjir"]
    counter = Value('i', 0)
    with Pool(1) as pool:
        p = Pool(1, initializer=counter_handler, initargs=(counter,))
        i = p.map_async(Proses, data, chunksize=1)
        i.wait()

been searching for hours but still no clue and i think maybe this is a duplcate quetions and i know it but i still can't find any answers. Is there any way to pass my xyz variable to my function?

Answer 1

As you have written in your example, Pool has initializer= and initargs= parameters which you can use to initialize the global variables as well:

from multiprocessing import Pool, Value


def Proses(lines):
    global xyz

    print(lines)
    print(xyz)


def Dosomething():
    a = [i for i in range(10)]
    return a


def init_pool(a, cnt):
    global xyz, counter
    xyz = a
    counter = cnt


if __name__ == "__main__":
    # i want to share xyz variable
    xyz = Dosomething()

    data = ["bjir", "bjir", "bjir"]
    counter = Value("i", 0)

    with Pool(1, initializer=init_pool, initargs=(xyz, counter)) as pool:
        i = pool.map_async(Proses, data, chunksize=1)
        i.wait()

Prints:

bjir
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
bjir
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
bjir
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]