I'm trying to catch a Queue.Empty exception that is raised if a multiprocessing.Queue is empty. The following does not work:
import multiprocessing
f = multiprocessing.Queue()
try:
f.get(True,0.1)
except Queue.Empty:
print 'foo'
This gives me a name error: NameError: name 'Queue' is not defined
replacing Queue.Empty with multiprocessing.Queue.Empty does not help either. In this case it gives me a "AttributeError: 'function' object has no attribute 'Empty'" exception.
The Empty exception you're looking for isn't available directly in the multiprocessing module, because multiprocessing borrows it from the queue module (which used to be named Queue in Python 2). To make your code work, just do an import queue at the top:
Try this:
import multiprocessing
import queue # or Queue in Python 2
f = multiprocessing.Queue()
try:
f.get(True,0.1)
except queue.Empty: # queue here refers to the module, not a class
print('foo')
multiprocessing should (and does) use isinstance(exception, Queue.Empty) (Queue is a module) because multiprocessing emulates threading api that often used with Queue.Queue and exceptions are part of the api.
multiprocessing.queues.Empty is Queue.Empty (just imported there for multiprocessing.queues.Queue to use). I'll update the answer.
import Queue ? Also how do you figure that out? There was nothing about needing to import Queue from the documentation of multiprocessing.multiprocessing) can use objects (e.g., raise exceptions) that are defined in other modules (in this case Empty name is defined in Queue module). The docs say that multiprocessing.Queue is a near clone of Queue.Queue. It means you should expect the same api: available methods, their arguments, exceptions raised are the same unless specified otherwise. And Queue.Queue documents when it raises Queue.Empty.Blckknght's answer from back in 2012 is still correct, however using Python 3.7.1 I discovered that you have to use queue.Empty as the name of the exception to catch (Note the lowercase 'q' in 'queue'.)
So, to recap:
import queue
# Create a queue
queuevarname = queue.Queue(5) # size of queue is unimportant
while some_condition_is_true:
try:
# attempt to read queue in a way that the exception could be thrown
queuedObject = queuevarname.get(False)
...
except queue.Empty:
# Do whatever you want here, e.g. pass so
# your loop can continue, or exit the program, or...
