Cameron Simpson wrote:
On 19Jan2010 23:01, MRAB <python@mrabarnett.plus.com> wrote: | Georg Brandl wrote: | >Am 19.01.2010 21:20, schrieb cool-RR: | >>On Tue, Jan 19, 2010 at 11:10 PM, Simon Brunning <simon@brunningonline.net>: | >> 2010/1/19 cool-RR <cool-rr@cool-rr.com>: | >> > Is there a reason that queues don't have an `__iter__` method? I | >> > mean both `Queue.Queue` and `multiprocessing.Queue`. | >> | >> Could it be made threadsafe? | >> | >>For me, iterating on the queue means just calling `get` repeatedly until | >>it's empty. Now that I think about it, maybe this is not the most | >>obvious meaning? I'm not sure now. | | >Your obvious queue iterator would call get(block=False) and stop on Empty. | >The other obvious meaning is be to call get(block=True) forever. IMO they | >are both too "obvious" to make a call -- an explicit while loop is better. | > | To me the 'obvious' meaning is to call get(block=True) and have it raise | Empty (actually, StopIteration) when the queue is empty and the 'sender' | has somehow signalled that no more items will be put into the queue | (q.finished()?). This would also eliminate the need for a sentinel!
Personally, I have long had an IterableQueue subclass, but it uses a tunable sentinel (None by default).
But it adds a .close() method, and doesn't iterate until empty, it iterates until closed. This is because I want to write a handler like so:
for item in Q: ...do stuff...
and have it block if the queue is empty.
So clearly there are two reasonable approaches to the end-of-iteration idea; extending Queue to do iteration probably would want to choose one.
So maybe two helper iteration methods might be the go: it's easy enough to write a generator to iterate-until-empty or iterate-until-sentinel.
Ah, yes, .close() would be better. :-) As for iterate-until-empty or iterate-until-sentinel, perhaps only a keyword argument is needed when the queue is created. Another possible feature (although this might be going too far) is a keyword argument for the number of 'producers' (default=1). Each can close the queue when it's finished, and StopIteration will be raised only when all have closed and the queue is empty.