Related to discussions on the notebook and extending the core Sage infrastructure, I stumbled across a thread on the twisted mailing list
http://twistedmatrix.com/pipermail/twisted-python/2009-July/020069.html which discusses a new introduction to asynchronous programming, why its good / necessary / important and not all that difficult. The report url is: http://mumak.net/stuff/twisted-intro.html Also, there's a small example on StackOverflow by Glyph which does a pretty good job at de-mystifying some of the Asynchronous mystique. http://stackoverflow.com/questions/80617/asychronous-programming-in-python-twisted/81456#81456 There's also an "in the works" part of the twisted document which attempts to clarify what was a simply awful part of the previous twisted documentation http://ezyang.com/twisted/defer2.html In the thread itself is a comment by Terry Jones which I include here > 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 -- Glenn H. Tarbox, PhD || 206-274-6919 http://www.tarbox.org --~--~---------~--~----~------------~-------~--~----~ To post to this group, send an email to sage-devel@googlegroups.com To unsubscribe from this group, send an email to sage-devel-unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/sage-devel URLs: http://www.sagemath.org -~----------~----~----~----~------~----~------~--~---
