Python pool.map makes the rest of my script gets executed more often

Question

Using my sample script

from multiprocessing import Pool


def methodUsingPool(x):
    if __name__ == '__main__':
        pool = Pool()
        pool.map(print, x)


methodUsingPool("x")
print("1")

gets the output

while I've been expecting

x
1

Why is that so? What can I do?

Can't replicate the problem with your code. Are you sure it's the only place where it is run? Also you could close or terminate the pool: https://docs.python.org/3/library/multiprocessing.html#multiprocessing.pool.Pool — haxor789, Feb 24 '22 at 12:03
And in addition to the fine answer by Olvin, you can read more here: https://stackoverflow.com/questions/419163/what-does-if-name-main-do about what is going on. The first answer gives an explicit explanation and show case. — Cow, Feb 24 '22 at 12:06

score 2 · Accepted Answer · answered Feb 24 '22 at 12:05

Behaviour will depend on your operating system. On macOS (for example) you will get similar output to what you've shown.

However, if you do this:

from multiprocessing import Pool

def methodUsingPool(x):
    with Pool() as pool:
        pool.map(print, x)

if __name__ == '__main__':
    methodUsingPool("x")
    print("1")

...you'll get your expected output regardless of platform

See: Python 3 multiprocessing

Python pool.map makes the rest of my script gets executed more often

1 Answers1