On Tuesday, 5 May 2015 18:48:09 UTC+1, Ian wrote: > Fundamentally, a future is a placeholder for something that isn't > available yet. You can use it to set a callback to be called when that > thing is available, and once it's available you can get that thing > from it.
OK, that makes a lot of sense. There seems to be two distinct strands within the asyncio world, the callback model and the task/coroutine model. AIUI, coroutines/tasks are supposed to let you avoid callbacks. So I guess in that model, a Future isn't something you should use directly in task-based code, because it works via callbacks. And yet tasks are futures, so it's not that simple :-) > In asyncio, a Task is a a Future that serves as a placeholder for the > result of a coroutine. The event loop manages callbacks, and that's > all it does. Um, I thought it scheduled tasks? > An event that it's been told to listen for occurs, and > the event loop calls the callback associated with that event. The Task > manages a coroutine's interaction with the event loop; when the > coroutine yields a future, the Task instructs the event loop to listen > for the completion of that future, setting a callback that will resume > the coroutine. OK, that (to an extent) explains how the callback and task worlds link together. That's useful. > The coroutines themselves are not that interesting of an interface; > all you can do with them is resume them. The asynchronous execution > done by asyncio is all based on futures. Because a coroutine can > easily be wrapped in a Task, this allows for coroutines to be used > anywhere a future is expected. And yet, futures are callback-based whereas tasks are suspension-point (yield from) based. I get a sense of what you're saying, but it's not very clear yet :-) > I don't know if I've done a good job explaining, but I hope this helps. It's all helping. It's a shame the docs don't do a better job of explaining the underlying model, to be honest, but I do feel like I'm slowly getting closer to an understanding. It's no wonder terminology is such a hot topic in the discussion of the new async PEP on python-dev :-( Paul -- https://mail.python.org/mailman/listinfo/python-list
