On Thu, Jul 30, 2009 at 4:27 PM, Terry Jones <te...@jon.es> wrote: > > Right. Everything you could do synchronously, you can do asynchronously > > (and a bit more too). It just /looks/ really weird. > > At some point I realized that it helps to realize that code that looks > synchronous really isn't at all. Probably all the programming that almost > all of us will ever do is not synchronous. You type > > x = y + 3 > > and you get into the habit of thinking that x just got assigned the value > of y + 3. But there's a whole set of levels of operations, all invisible to > you, that are frantically rearranging atoms behind the scenes to pull off > this tiny miracle. Instead of trying to wrap your head around the so-called > "weird" asynchronous operation of Twisted, it's easier to let fall the > comforting illusion that you're in the synchronous world to begin with - > whatever that's supposed to mean (it's more like a fairy tale IMO). You're > not. > > It's more accurate to think that that line of code arranges for x to > *eventually* hold the value of y + 3. Then it's a small step to thinking > that > > x = y + 3 > z = f(x) > > is just another slightly bigger part of the same illusion. Those lines of > code aren't executed one after another at all. You're just brought up with > the fairy tale that they are - or at least you study computer science and > spend so much time with high-level languages that you start to take it for > granted that they are done one after the other. But the second line is > *eventually* executed after the first, assuming nothing went wrong (e.g., y > could be None). > > At that point - everything is asynchronous - you have the right mindset to > think perfectly clearly about Twisted code. And there's no jump to make at > all. The only things you have to get your head around are 1) the fact that > Twisted code doesn't give you the comforting linear illusion of so-called > synchronous code as you type it in your editor (inlineCallbacks helps a lot > with improving that), and 2) that Twisted's deferreds are the way of > maintaining the flow of results (both correct and incorrect) through time > as your program executes. I.e., you've lost the step-at-a-time line-by-line > results computed on line N are available on line N+1 flow of code you can > so easily read in your editor, and in exchange you have deferreds. > > I could go on, obviously :-) But I just wanted to point out that the shift > from thinking "synchronously" to "asynchronously" is much easier to make if > you realize the former is a convenient illusion and in fact you've always > been doing things asynchronously. > > Terry >
Thanks for this, Terry. I'd never thought of it that way, and it's quite a good point. Kevin Horn
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