Queue enhancement suggestion

[Paul Rubin]

I'd like to suggest adding a new operation

   Queue.finish()

This puts a special sentinel object on the queue.  The sentinel
travels through the queue like any other object, however, when
q.get() encounters the sentinel, it raises StopIteration instead
of returning the sentinel.  It does not remove the sentinel from
the queue, so further calls to q.get also raise StopIteration.
That permits writing the typical "worker thread" as

   for item in iter(q.get): ...

without having to mess with the task-counting stuff that recently got
added to the Queue module.  The writing end of the queue simply
calls .finish() when it's done adding items.

Someone in an earlier thread suggested

     # writing side
     sentinel = object()
     q.put(sentinel)

     ...
     # reading side
     for item in iter(q.get, sentinel): ...

however that actually pops the sentinel, so if there are a lot of
readers then the writing side has to push a separate sentinel for
each reader.  I found my code cluttered with

    for i in xrange(number_of_worker_threads):
       q.put(sentinel)

which certainly seems like a code smell to me.