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My Queue usage typically involves a producer thread and a consumer thread. The producer calls queue.put(value) until it's done at which point it calls queue.put(sentinel). My consumers almost always look like this:

while True:     value = queue.get()     if value != sentinel:         # do something with value     else:         break

That logic can be abstracted away into a generator function that allows consumer code to look like this instead:

for value in iterQueue(queue, sentinel):     # do something with value

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def iterQueue(queue, sentinel):
    """Iterate over the values in queue until sentinel is reached."""
    while True:
        value = queue.get()
        if value != sentinel:
            yield value
        else:
            return

Generators functions provide a powerful tool for abstracting looping logic into separate functions. This can make code much easier to read.

2 comments

Paul Moore 17 years, 6 months ago  # | flag

This is built in (but fairly obscure!). You don't need this - the built in iter() function allows you to do this:

for val in iter(queue.get, sentinel):
    # process val

Until I saw this recipe, I'd forgotten about it, though!

Ori Peleg 16 years ago  # | flag

Cool! I want to pass arguments to Queue.get as well, so I added:

def iterQueue(queue, sentinel, **kwargs):
...
   value = queue.get(**kwargs)
...

Now I can

iterQueue(queue, sentinel, timeout=10)

to my heart's desire :-)

Created by Jimmy Retzlaff on Thu, 4 Dec 2003 (PSF)
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