Cannot access Queue.Empty: "AttributeError: 'function' object has no attribute 'Empty'"

Question

For some reason I can't access the Queue.Empty exception - what am I doing wrong here?

from multiprocessing import Process, Queue

# ...

try:
    action = action_queue.get(False)
    print "Action: " + action
except Queue.Empty:
    pass

The stack trace:

Traceback (most recent call last):  
File "C:\Program Files\Python27\lib\multiprocessing\process.py", line 258,
  in _bootstrap
  self.run()
File "C:\Program Files\Python27\lib\multiprocessing\process.py", line 114,
  in run
  self._target(*self._args, **self._kwargs)
File "D:\Development\populate.py", line 39, in permutate
  except Queue.Empty: AttributeError: 'function' object has no attribute 'Empty'

Kingpin2k · Accepted Answer · 2020-04-07 02:15:58Z

28

The Queue.Empty exception is in the Queue module, not in the multiprocessing.queues.Queue class. The multiprocessing module actually uses the Queue (module) Empty exception class:

from multiprocessing import Queue
from Queue import Empty
q = Queue()
try:
    q.get( False )
except Empty:
    print "Queue was empty"

If you want to be very explicit and verbose, you can do this:

import multiprocessing
import Queue
q = multiprocessing.Queue()
try:
    q.get( False )
except Queue.Empty:
    print "Queue was empty"

Favoring the former approach is probably a better idea because there is only one Queue object to worry about and you don't have to wonder if you are working with the class or the module as in my second example.

edited Apr 7, 2020 at 2:15

Kingpin2k

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answered Jun 27, 2011 at 11:23

underrun

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5 Comments

Ross Over a year ago

Ah I see now, I thought importing Queue imported the module, rather than the class. Thanks!

underrun Over a year ago

it's even more interesting -- importing from multiprocessing import Queue imports the Queue function from the __init__.py in multiprocessing which returns the Queue class from the multiprocessing.queues sub module. Duck typing and namespaces make for interesting programming!

Source Matters Over a year ago

Just a note, this answer has a typo in "execpt" for the copy/paste coders, and the import statement should be lowercase Queue.

Rotkiv Over a year ago

from multiprocessing import Queue \ from Queue import Empty gives me ModuleNotFoundError: No module named 'Queue' :(

Rotkiv Over a year ago

OK. for those with similar issue see stackoverflow.com/questions/33432426/… tldr it has to be "Joinable Queue" in py3

theRPGmaster · Accepted Answer · 2023-07-11 13:28:29Z

1

In Python 3, this is one way to do it. Note the lowercase 'queue':

from multiprocessing import Queue
from queue import Empty as QueueEmpty
q = Queue()
try:
    q.get(False)
except QueueEmpty:
    print "Queue was empty"

answered Jul 11, 2023 at 13:28

theRPGmaster

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