On Sun, Mar 7, 2010 at 11:56 AM, P.J. Eby <pje@telecommunity.com> wrote:
At 10:59 AM 3/7/2010 -0800, Jeffrey Yasskin wrote:
So is it that you just don't like the idea of blocking, and want to stop anything that relies on it from getting into the standard library?
Um, no. As I said before, call it a "parallel task queue" or "parallel task manager" or something to that general effect and I'm on board.
It may not be in the Zen of Python, but ISTM that names should generally follow use cases. It is something of a corollary to "one obvious way to do it", in that if you see something whose name matches what you want to do, then it should be obvious that that's the way in question. ;-)
The use cases for "parallel task queues", however, are a subset of those for "futures" in the general case. Since the proposed module addresses most of the former but very little of the latter, calling it futures is inappropriate.
Specifically, it's:
1. Confusing to people who don't know what futures are (see e.g R.D. Murray's post), and
This is not a problem. We will document what we consider a future.
2. Underpowered for people who expect/want a more fully-featured futures system along the lines of E or Deferreds.
This sounds like an underhanded slur towards the PEP.
It seems that the only people for whom it's an intuitively correct description are people who've only had experience with more limited futures models (like Java's). However, these people should not have a problem understanding the notion of parallel task queueing or task management, so changing the name isn't really a loss for them, and it's a gain for everybody else.
I expect that the majority of Python users fall either in camp #1 (never heard of futures, will be happy to learn about what Python calls futures) or camp #3 (have used Java futures). The users of E can be counted on a few hands. Deferreds are used heavily in some Python circles but most Python users (myself included) have at most a very vague idea of them. Also, as you clarify below, Deferreds are so much more powerful that they can't possibly be mistaken for futures (as defined by this PEP). Plus they already have a name.
Given the set_result and set_exception methods, it's pretty straightforward to fill in the value of a future from something that isn't purely computational.
Those are described as "internal" methods in the PEP; by contrast, the Deferred equivalents are part of the public API.
Given a way to register "on-done" callbacks with the future, it would be straightforward to wait for a future without blocking, too.
Yes, and with a few more additions besides that one, you might be on the way to an actual competitor for Deferreds. For example: retry support, chaining, logging, API for transparent result processing, coroutine support, co-ordination tools like locks, sempaphores and queues, etc.
These are all things you would very likely want or need if you actually wanted to write a program using futures as *your main computational model*, vs. just needing to toss out some parallel tasks in a primarily synchronous program.
Of course, Deferreds are indeed overkill if all you're ever going to want is a few parallel tasks, unless you're already skilled in using Twisted or some wrapper for it.
So, I totally support having a simple task queue in the stdlib, as there are definitely times I would've used such a thing for a quick script, if it were available.
However, I've *also* had use cases for using futures as a computational model, and so that's what I originally thought this PEP was about. After the use cases were clarified, though, it seems to me that *calling* it futures is a bad idea, because it's really just a nice task queuing system.
I'm +1 on adding a nice task queuing system, -1 on calling it by any other name. ;-)
So let's focus on the functionality of the task queuing system, and stick to roughly the functionality proposed in the PEP. The name is a non-issue and further discussion ought to be sent to null-dev@python.org. -- --Guido van Rossum (python.org/~guido)