The problem is not with the code / Python 3.6, it is with Spyder.

After some investigation I found that the code runs fine when executed in an external system terminal but not when run in Spyder's IPython console.

I was able to dump the contents of spec and assign them to a variable that was included inside main to allow this code to function within the IPython console.

from multiprocessing import Pooldef f(x):    return x*xif __name__ == '__main__':    __spec__ = "ModuleSpec(name='builtins', loader=<class '_frozen_importlib.BuiltinImporter'>)"    with Pool(5) as p:       print (p.map(f, [1, 2, 3]))

pdb users

The question didn't specifically mention Spyder nor Conda (though it is tagged as such). Hence, I will note that I found this can also happen when using pdb.

E.g.

python -m pdb myprogram.py

Passing __spec__ = None would be a useful workaround if you wanted to persist with pdb.

the same probelm in Spyder (Anaconda3, python 3.6) when I try the external terminal.

Error message: AttributeError: module '__main__' has no attribute '__spec__'

I changed the Run console to 'Excute in current console', and applied it.then if that doesnot work, try other conselor and then change back to 'Excute in current console'.Finally, it works.no '__spec__ = None' is needed.