I decided to try and get into the multiprocessor module to help speed up my program. To figure it out, I tried using some of the code examples on the official python documentation on multiprocessing.

First attempt: Introduction

>>> from multiprocessing import Pool
>>>
>>> def f(x):
...     return x*x
...
>>> if __name__ == '__main__':
...     with Pool(5) as p:
...         print(p.map(f, [1, 2, 3]))
...
Process SpawnPoolWorker-3:
Process SpawnPoolWorker-2:
Traceback (most recent call last):File "C:\Program Files\Python36\lib\multiprocessing\process.py", line 258, in _bootstrapself.run()File "C:\Program Files\Python36\lib\multiprocessing\process.py", line 93, in runself._target(*self._args, **self._kwargs)File "C:\Program Files\Python36\lib\multiprocessing\pool.py", line 108, in workertask = get()File "C:\Program Files\Python36\lib\multiprocessing\queues.py", line 337, in getreturn _ForkingPickler.loads(res)
AttributeError: Can't get attribute 'f' on <module '__main__' (built-in)>
Traceback (most recent call last):File "C:\Program Files\Python36\lib\multiprocessing\process.py", line 258, in _bootstrapself.run()File "C:\Program Files\Python36\lib\multiprocessing\process.py", line 93, in runself._target(*self._args, **self._kwargs)File "C:\Program Files\Python36\lib\multiprocessing\pool.py", line 108, in workertask = get()File "C:\Program Files\Python36\lib\multiprocessing\queues.py", line 337, in getreturn _ForkingPickler.loads(res)
AttributeError: Can't get attribute 'f' on <module '__main__' (built-in)>
Process SpawnPoolWorker-4:
Traceback (most recent call last):File "C:\Program Files\Python36\lib\multiprocessing\process.py", line 258, in _bootstrapself.run()File "C:\Program Files\Python36\lib\multiprocessing\process.py", line 93, in runself._target(*self._args, **self._kwargs)File "C:\Program Files\Python36\lib\multiprocessing\pool.py", line 108, in workertask = get()File "C:\Program Files\Python36\lib\multiprocessing\queues.py", line 337, in getreturn _ForkingPickler.loads(res)
AttributeError: Can't get attribute 'f' on <module '__main__' (built-in)>

Here I assume that the pool function is broken; maybe there is a typo somewhere in the lastest version. So I try some of the more specific code.

Second attempt: Process class code block 2

>>> from multiprocessing import Process
>>> import os
>>>
>>> def info(title):
...     print(title)
...     print('module name:', __name__)
...     print('parent process:', os.getppid())
...     print('process id:', os.getpid())
...
>>> def f(name):
...     info('function f')
...     print('hello', name)
...
>>> if __name__ == '__main__':
...     info('main line')
...     p = Process(target=f, args=('bob',))
...     p.start()
...     p.join()
...
main line
module name: __main__
parent process: 43824
process id: 54888
Traceback (most recent call last):File "<string>", line 1, in <module>File "C:\Program Files\Python36\lib\multiprocessing\spawn.py", line 105, in spawn_mainexitcode = _main(fd)File "C:\Program Files\Python36\lib\multiprocessing\spawn.py", line 115, in _mainself = reduction.pickle.load(from_parent)
AttributeError: Can't get attribute 'f' on <module '__main__' (built-in)>

At this point I know the underlying error is with the Process function of multiprocessing. However, I think that the extended code might have broken something, so I try the simple code.

Third Attempt Process class code block 1

>>> from multiprocessing import Process
>>>
>>> def f(name):
...     print('hello', name)
...
>>> if __name__ == '__main__':
...     p = Process(target=f, args=('bob',))
...     p.start()
...     p.join()
...
Traceback (most recent call last):File "<string>", line 1, in <module>File "C:\Program Files\Python36\lib\multiprocessing\spawn.py", line 105, in spawn_mainexitcode = _main(fd)File "C:\Program Files\Python36\lib\multiprocessing\spawn.py", line 115, in _mainself = reduction.pickle.load(from_parent)
AttributeError: Can't get attribute 'f' on <module '__main__' (built-in)>

At this point I was desperate. I think that maybe the argument was messing with the Process class.

Final attempt: self-generated code

>>> from multiprocessing import Process
>>>
>>> def f():
...     print('hello')
...
>>> if __name__ == '__main__':
...     p = Process(target=f)
...     p.start()
...     p.join()
...
Traceback (most recent call last):File "<string>", line 1, in <module>File "C:\Program Files\Python36\lib\multiprocessing\spawn.py", line 105, in spawn_mainexitcode = _main(fd)File "C:\Program Files\Python36\lib\multiprocessing\spawn.py", line 115, in _mainself = reduction.pickle.load(from_parent)
AttributeError: Can't get attribute 'f' on <module '__main__' (built-in)>

Now I am totally confused because I do not know why the error is occuring. Could someone help me figure out why I am getting this error every time?

You're in interactive mode. That basically doesn't work with multiprocessing, because the workers have to import __main__ and get something that mostly resembles the main process's __main__. This is one of the many ways in which the multiprocessing API is horribly confusing.

Put your code in a script and run the script.