How to iterate Queue.Queue items in Python?

问题

Does anyone know a pythonic way of iterating over the elements of a Queue.Queue without removing them from the Queue. I have a producer/consumer-type program where items to be processed are passed by using a Queue.Queue, and I want to be able to print what the remaining items are. Any ideas?

回答1:

You can loop over a copy of the underlying data store:

for elem in list(q.queue)

Eventhough this bypasses the locks for Queue objects, the list copy is an atomic operation and it should work out fine.

If you want to keep the locks, why not pull all the tasks out of the queue, make your list copy, and then put them back.

mycopy = []
while True:
     try:
         elem = q.get(block=False)
     except Empty:
         break
     else:
         mycopy.append(elem)
for elem in mycopy:
    q.put(elem)
for elem in mycopy:
    # do something with the elements

回答2:

Listing queue elements without consuming them:

>>> from Queue import Queue
>>> q = Queue()
>>> q.put(1)
>>> q.put(2)
>>> q.put(3)
>>> print list(q.queue)
[1, 2, 3]

After operation, you can still process them:

>>> q.get()
1
>>> print list(q.queue)
[2, 3]

回答3:

You can subclass queue.Queue to achieve this in a thread-safe way:

import queue


class ImprovedQueue(queue.Queue):
    def to_list(self):
        """
        Returns a copy of all items in the queue without removing them.
        """

        with self.mutex:
            return list(self.queue)

来源：https://stackoverflow.com/questions/8196254/how-to-iterate-queue-queue-items-in-python

标签

python

queue

producer-consumer