Question

I need to know when a Queue is closed and wont have more items so I can end the iteration.

I did it by putting a sentinel in the queue:

from Queue import Queue

class IterableQueue(Queue): 

    _sentinel = object()

    def __iter__(self):
        return self

    def close(self):
        self.put(self._sentinel)

    def next(self):
        item = self.get()
        if item is self._sentinel:
            raise StopIteration
        else:
            return item

Given that this is a very common use for a queue, isn’t there any builtin implementation?

Answer 1

A sentinel is a reasonable way for a producer to send a message that no more queue tasks are forthcoming.

FWIW, your code can be simplified quite a bit with the two argument form of iter():

from Queue import Queue

class IterableQueue(Queue): 

    _sentinel = object()

    def __iter__(self):
        return iter(self.get, self._sentinel)

    def close(self):
        self.put(self._sentinel)