On Jun 11, 10:13 am, Jean-Paul Calderone <[EMAIL PROTECTED]> wrote: > On Tue, 10 Jun 2008 22:46:37 -0700 (PDT), George Sakkis <[EMAIL PROTECTED]> > wrote: > >On Jun 10, 11:47 pm, Larry Bates <[EMAIL PROTECTED]> wrote: > > >> I had a little trouble understanding what exact problem it is that you are > >> trying to solve but I'm pretty sure that you can do it with one of two > >> methods: > > >Ok, let me try again with a different example: I want to do what can > >be easily done with 2.5 Queues using Queue.task_done()/Queue.join() > >(see example athttp://docs.python.org/lib/QueueObjects.html), but > >instead of having to first put all items and then wait until all are > >done, get each item as soon as it is done. > > >> 1) Write the producer as a generator using yield method that yields a > >> result > >> every time it is called (something like os.walk does). I guess you could > >> yield > >> None if there wasn't anything to consume to prevent blocking. > > >Actually the way items are generated is not part of the problem; it > >can be abstracted away as an arbitrary iterable input. As with all > >iterables, "there are no more items" is communicated simply by a > >StopIteration. > > >> 2) Usw somethink like Twisted insted that uses callbacks instead to handle > >> multiple asynchronous calls to produce. You could have callbacks that > >> don't do > >> anything if there is nothing to consume (sort of null objects I guess). > > >Twisted is interesting and very powerful but requires a different way > >of thinking about the problem and designing a solution. More to the > >point, callbacks often provide a less flexible and simple API than an > >iterator that yields results (consumed items). For example, say that > >you want to store the results to a dictionary. Using callbacks, you > >would have to explicitly synchronize each access to the dictionary > >since they may fire independently. > > This isn't true. Access is synchronized automatically by virtue of the > fact that there is no pre-emptive multithreading in operation. This is > one of the many advantages of avoiding threads. :) There may be valid > arguments against callbacks, but this isn't one of them. > > Jean-Paul
Thanks for the correction; that's an important advantage for callbacks in this case. George -- http://mail.python.org/mailman/listinfo/python-list
