Ronald Oussoren <> added the comment:

Multiprocessing by default uses the fork system call to start new processes on 
Linux. This system call is not available on Windows, and there multiprocessing 
starts a fresh interpreter (see 

I'm also on macOS, and cannot reproduce the problem there even when using the 
'spawn' method there by adding some lines to the start of your script (before 
the other import statements):

import multiprocessing
if __name__ == "__main__":

But: I have a fairly old version of 3.6 on my machine.


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