Chapter 5 - Listing 5.1 Introduction to multiprocessing

[aryanphd]

import multiprocessing as mp
import numpy as np
def square(x): #A
return np.square(x)
x = np.arange(64) #B
print(x)
print(mp.cpu_count())
pool = mp.Pool(4) #C

squared = pool.map(square, [x[8i:8i+8] for i in range(4)])
print(squared)

Unfortunately, I receive the following error after running the code.

print(squared)
[ 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23
24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47
48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63]
4

Process SpawnPoolWorker-9:
Traceback (most recent call last):
File "C:\ProgramData\Anaconda3\lib\multiprocessing\process.py", line 315, in _bootstrap
self.run()
File "C:\ProgramData\Anaconda3\lib\multiprocessing\process.py", line 108, in run
self._target(*self._args, **self._kwargs)
File "C:\ProgramData\Anaconda3\lib\multiprocessing\pool.py", line 114, in worker
task = get()
File "C:\ProgramData\Anaconda3\lib\multiprocessing\queues.py", line 358, in get
return _ForkingPickler.loads(res)
AttributeError: Can't get attribute 'square' on <module 'main' (built-in)>
Process SpawnPoolWorker-10:
Traceback (most recent call last):
File "C:\ProgramData\Anaconda3\lib\multiprocessing\process.py", line 315, in _bootstrap
self.run()
File "C:\ProgramData\Anaconda3\lib\multiprocessing\process.py", line 108, in run
self._target(*self._args, **self._kwargs)
File "C:\ProgramData\Anaconda3\lib\multiprocessing\pool.py", line 114, in worker
task = get()
File "C:\ProgramData\Anaconda3\lib\multiprocessing\queues.py", line 358, in get
return _ForkingPickler.loads(res)
AttributeError: Can't get attribute 'square' on <module 'main' (built-in)>
Process SpawnPoolWorker-11:
Traceback (most recent call last):
File "C:\ProgramData\Anaconda3\lib\multiprocessing\process.py", line 315, in _bootstrap
self.run()
File "C:\ProgramData\Anaconda3\lib\multiprocessing\process.py", line 108, in run
self._target(*self._args, **self._kwargs)
File "C:\ProgramData\Anaconda3\lib\multiprocessing\pool.py", line 114, in worker
task = get()
File "C:\ProgramData\Anaconda3\lib\multiprocessing\queues.py", line 358, in get
return _ForkingPickler.loads(res)
AttributeError: Can't get attribute 'square' on <module 'main' (built-in)>
Process SpawnPoolWorker-12:
Traceback (most recent call last):
File "C:\ProgramData\Anaconda3\lib\multiprocessing\process.py", line 315, in _bootstrap
self.run()
File "C:\ProgramData\Anaconda3\lib\multiprocessing\process.py", line 108, in run
self._target(*self._args, **self._kwargs)
File "C:\ProgramData\Anaconda3\lib\multiprocessing\pool.py", line 114, in worker
task = get()
File "C:\ProgramData\Anaconda3\lib\multiprocessing\queues.py", line 358, in get
return _ForkingPickler.loads(res)
AttributeError: Can't get attribute 'square' on <module 'main' (built-in)>

[garybake]

This looks to be a problem with the way python handles multiprocessing. https://stackoverflow.com/questions/41385708/multiprocessing-example-giving-attributeerror