On 04Dec2013 09:44, Helmut Jarausch <jarau...@igpm.rwth-aachen.de> wrote:
> On Wed, 04 Dec 2013 08:13:03 +1100, Cameron Simpson wrote:
> > I iterate over Queues so often that I have a personal class called
> > a QueueIterator which is a wrapper for a Queue or PriorityQueue
> > which is iterable, and an IterablePriorityQueue factory function.
> > Example:
> >
> > from cs.queues import IterablePriorityQueue
> >
> > IPQ = IterablePriorityQueue()
> > for item in [1,2,3,7,6,5,9,4]:
> > IPQ.put(item)
> >
> > for item in IPQ:
> > ... do stuff with item ...
>
> Many thanks!
> I think you QueueIterator would be a nice addition to Python's library.
I'm not convinced. I'm still sorting out the edge cases, and it's
my own code and use cases!
The basic idea is simple enough:
class QueueIterator:
def __init__(self, Q, sentinel=None):
self.q = Q
self.sentinel = sentinel
def __next__(self):
item = self.q.get()
if item is self.sentinel:
# queue sentinel again for other users
self.q.put(item)
raise StopIteration
return item
def put(self, item):
if item is self.sentinel:
raise ValueError('.put of sentinel object')
return self.q.put(item)
def close(self):
self.q.put(self.sentinel)
QI = QueueIterator(Queue())
Note that it does not work well for PriorityQueues unless you can
ensure the sentinel sorted later than any other item.
But you really need to be sure nobody does a .get() in the internal
queue, or the close protocol doesn't work. This is why the above
does not expose a .get() method.
You want to prevent .put() on the queue after close().
Of course, I have use cases where I _want_ to allow .put() after
close:-(
You may want to issue a warning if more than one call to
.close happens.
And so on.
And I have a some weird cases where the close situation has trouble,
which probably points to .close() not being a great mapping to
my termination scenarios.
It is easy to code for the simple data-in, data-out case though.
Cheers,
--
Cameron Simpson <c...@zip.com.au>
Computer manufacturers have been failing to deliver working systems on
time and to budget since Babbage. - Jack Schofield, in The Guardian
--
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