On Fri, 10 Feb 2006 16:49:13 +1300, Greg Ewing <[EMAIL PROTECTED]> wrote: >Valentino Volonghi aka Dialtone wrote: > >> when some_operation_that_results_in_a_deferred() -> result: >> if result == 'Initial Value': >> when work_on_result_and_return_a_deferred(result) -> inner_res: >> print inner_res >> else: >> print "No work on result" >> reactor.stop() > >Hmmm. This looks remarkably similar to something I got half >way through dreaming up a while back, that I was going to >call "Simple Continuations" (by analogy with "Simple Generators"). >Maybe I should finish working out the details and write it up. > >On the other hand, it may turn out that it's subsumed by >the new enhanced generators plus a trampoline.
This in only partially true. In fact, let's consider again twisted for the example, you can do something like this: @defgen def foo(): for url in urls: page = yield client.getPage(url) print page This has 2 disadvantages IMHO. First of all I have to use a function or a method decorated with @defgen to write that. But most important that code, although correct is serializing things that could be parallel. The solution is again simple but not really intuitive: @defgen def foo(): for d in map(client.getPage, urls): page = yield d print page Written in this way it will actually work in a parallel way but it is not really an intuitive solution. Using when instead: for url in urls: when client.getPage(url) -> page: print page This wouldn't have any problem and is quite readable. A similar construct is used in the E language and here http://www.skyhunter.com/marcs/ewalnut.html#SEC20 is explained how when works for them and their promise object. You can also have multiple things to wait for: when (client.getPage(url), cursor.execute(query)) -> (page, results): print page, results or l = [list, of, deferreds] when l -> *results: print results and we could catch errors in the following way: when client.getPage(url) -> page: print page except socket.error, e: print "something bad happened" HTH -- Valentino Volonghi aka Dialtone Now Running MacOSX 10.4 Blog: http://vvolonghi.blogspot.com New Pet: http://www.stiq.it _______________________________________________ Python-Dev mailing list Python-Dev@python.org http://mail.python.org/mailman/listinfo/python-dev Unsubscribe: http://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com