multiprocessing AttributeError module object has no attribute '__path__'

Question

i have a long script which at the end needs to run a function to all items of huge list which takes a long time,consider for example:

input_a= [1,2,3,4] # a          


        

Answer 1

from multiprocessing import Pool as ThreadPool
import requests


API_URL = 'http://example.com/api'
pool = ThreadPool(4) # Hint...

def foo(x):
  params={'x': x}
  r = requests.get(API_URL, params=params)
  return r.json()

if __name__ == '__main__':
  num_iter = [1,2,3,4,5]
  out = pool.map(foo, num_iter)
  print(out)

Hint's Answer: This is why the exception is raised. Pool definition is outside if __name__ == '__main__'

Fixed...

from multiprocessing import Pool as ThreadPool
import requests


API_URL = 'http://example.com/api'

def foo(x):
  params={'x': x}
  r = requests.get(API_URL, params=params)
  return r.json()

if __name__ == '__main__':
  pool = ThreadPool(4) # Hint...
  num_iter = [1,2,3,4,5]
  out = pool.map(foo, num_iter)
  print(out)

The python docs touch on this scenario as well: https://docs.python.org/2/library/multiprocessing.html#using-a-pool-of-workers

I did not find this to be an issue when using multiprocessing.dummy at all.

Answer 2

Multiprocessing needs to be able to import your module, as stated at the top of the documentation.

You have a bunch of code sitting at module (global) scope, so this will be run every time the module is imported.

Put it within your if __name__ == '__main__' block, or better yet, in a function.