找不到arrribute的奇怪错误

Question

Have a piece of code when run from the repl generates an weird error on win 7

from multiprocessing import Process, Pool
import time
from urllib import request

def millis():
  return int(round(time.time() * 1000))

def http_get(url):
  start_time = millis()
  result = {"url": url, "data": request.urlopen(url, timeout=5).read()[:100]}
  print(url + " took " + str(millis() - start_time) + " ms")
  return result



start_time = millis()
if __name__ == "__main__":
  urls = ['http://www.google.com/', 'https://foursquare.com/', 'http://www.yahoo.com/', 'http://www.bing.com/', "https://www.yelp.com/"]
  pool = Pool(processes=5)
  results = pool.map(http_get, urls)
  print("\nTotal took " + str(millis() - start_time) + " ms\n")
  for result in results:
    print(result)

And the error is

Traceback (most recent call last):
  File "c:\python36\lib\multiprocessing\process.py", line 249, in _bootstrap
    self.run()
  File "c:\python36\lib\multiprocessing\process.py", line 93, in run
    self._target(*self._args, **self._kwargs)
  File "c:\python36\lib\multiprocessing\pool.py", line 108, in worker
    task = get()
  File "c:\python36\lib\multiprocessing\queues.py", line 345, in get
    return _ForkingPickler.loads(res)
AttributeError: Can't get attribute 'http_get' on <module '__main__' (built-in)>

I have no clue what i am doing wrong .Without multiprocessing it works like charm

Answer 1

From the multiprocessing documentation :

Note

Functionality within this package requires that the __main__ module be importable by the children. This is covered in Programming guidelines however it is worth pointing out here. This means that some examples, such as the multiprocessing.pool.Pool examples will not work in the interactive interpreter.