Error with multiprocessing with Thonny 3.3.13 under Windows10

Running this code fails.

import multiprocessing 
def y(x):
    print(x)
if __name__ == '__main__':
    f = multiprocessing.Process(target = y, args=('a'))
    f.start()
    f.join()

Errors:

Traceback (most recent call last):
  File "<string>", line 1, in <module>
  File "C:\Program Files (x86)\Thonny\lib\multiprocessing\spawn.py", line 105, in spawn_main
    exitcode = _main(fd)
  File "C:\Program Files (x86)\Thonny\lib\multiprocessing\spawn.py", line 115, in _main
    self = reduction.pickle.load(from_parent)
AttributeError: Can't get attribute 'y' on <module '__main__' (built-in)>

[aivarannamaa]

I’ll add a warning and suggestion for running via Terminal when Thonny’s backend detects importing multiprocessing.

[Ivoz]

I’ll test later, whether a6bafcc helped here as well

Applying this just in my 3.3.13 thonny worked as well, to get multiprocessing working. Line 133 under Thonny\Lib\site-packages\thonny\plugins\cpython\cpython_backend.py