Python multiprocessing module

Question

I'm researching about the multiprocessing module and found this 5 years old code.

After uncommented the last 2 lines and add a few extra printing, I come up with this code:

import multiprocessing as mp
def sqr(x):
print(f'x: {x}')
print(x**2)
return x**2

print(mp.cpu_count(), 'cpu count')

with mp.Pool(2) as p:
p.map(sqr, list(range(10)))

It runs fine in the playground.
However, when I copied it to IDLE and run it from there, it only prints the number of CPU counts and keep running but no output.
Then I switch to powershell and run it, it keeps outputting error message.
While the screen rolling fast, I notice
RuntimeError
if __name__ == '__main__':
freeze_support()

So I added it at the end, still not working in IDEL & powershell.

Then I use vscode, without the if statement, it runs fine without issue.
Can anyone explain?
https://sololearn.com/compiler-playground/cmaEN3hjgaXf/?ref=app

Answer 1

with idle, you have to first open a cmd terminal or powershell and type

python -m idlelib

this will make the terminal receive the idle run output and your complete output will be displayed here.

also, using
if __name__ == '__main__':
with mp.Pool(2) as p:
p.map(swr, list(range(10)))

is a good idea

if I used pwsh or cmd to run a saved python file with the multiprocessing code, I get the correct result, so I can't confirm that part.

Answer 2

I turned to Python module of the week https://pymotw.com/3/multiprocessing/basics.html
Created the first example in IDLE, saved in a file and run it the normal way, nothing happen.
Turn to powershell, python testing.py, and it runs.

Then I found this article.
https://stackoverflow.com/questions/35293178/can-multiprocessing-process-class-be-run-from-idle

As suggested, same as yours, run below command in terminal.
python -m idlelib
It opens another IDLE with a different icon.
Open my saved code from the new window, hit F5, nothing shows on IDLE, but it got printed in terminal...

Still scratching head...

Answer 3

from the SO discussion, it's a Windows Idle quirk.