Mailman 3 March 2006 - Edu-sig

Properties use case
by Arthur 06 Apr '06

06 Apr '06

I don't know whether this is theoretical, philosophical, or in any way relevant to what we are *supposed* to be discussing here - but to break what I consider to be an uncomfortable silence I thought I'd throw it out into the excess bandwidth, nonetheless: I do in fact use properties in various places in my code, and but not generally in ways I find compelling or truly functional - maybe some nuance of "interface" that I could easily live without. I seem , however, to have come across my first more compelling use case. I went with the creation of a mutable complex number type, which I then inherit from and use down the line. But when I send instances of classes derived from this custom type to use as elements of a Numeric Userarray, there is no way that I have found to be able to tell Numeric that if it treats these instances as if they were built-in complex numbers, things should work out OK. Numeric seems to insist on creating arrays of Python instances, and then insists it does not know how to do math with Python instances. So properties come in handy essentially to do casting - from the custom Complex type to the built-in complex type on the way into the UserArray, and in reverse on the way out - i.e, set and get. This only additionally meant customizing the Numeric UserArray to derive from object (it doesn't come that way) , before I go further with it, so that properties "take". I am sure I am taking at least a bit of a performance hit by going this route. Does anyone see something simple I may be missing here to get to where I am trying to get, without the hit? Art

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Rapunsel, Rapunsel
by Jonah Bossewitch 05 Apr '06

05 Apr '06

Does this group know about this project? http://maryflanagan.com/rapunsel/index.htm I saw Mary talk today and her work is quite impressive. It's still being researched... wouldn't it be wonderful if they moved away from java and towards a more youthful, dynamic, vibrant, language... /jsb

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Want to improve the python tutorial?
by Laura Creighton 29 Mar '06

29 Mar '06

>From doc-sig. Thank you Fredrik. Laura ------- Forwarded Message Return-Path: doc-sig-bounces(a)python.org Delivery-Date: Wed Mar 29 21:58:11 2006 From: "Fredrik Lundh" <fredrik(a)pythonware.com> Date: Wed, 29 Mar 2006 21:56:57 +0200 Lines: 13 Message-ID: <e0eoqc$c6k$1(a)sea.gmane.org> Subject: [Doc-SIG] introducing the experimental pytut wiki without further ado, here's http://pytut.infogami.com/ inspired by http://article.gmane.org/gmane.comp.python.general/455724 and related to several earlier threads on this mailing list. </F> _______________________________________________ Doc-SIG maillist - Doc-SIG(a)python.org http://mail.python.org/mailman/listinfo/doc-sig ------- End of Forwarded Message

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Maybe 'learn python with your kids' is an idea whose time has come?
by Laura Creighton 29 Mar '06

29 Mar '06

We could do this for Europython. Do we want to? What would we teach, and what would we need? Laura ------- Forwarded Message Return-Path: marketing-python-bounces(a)wingware.com Delivery-Date: Wed Mar 29 14:41:01 2006 Return-Path: <marketing-python-bounces(a)wingware.com> Received: from www.wingide.com (www.archaeopteryx.com [209.251.75.100]) Date: Tue, 28 Mar 2006 21:16:01 -0600 From: "Michael Tobis" <mtobis(a)gmail.com> To: marketing-python(a)wingware.com MIME-Version: 1.0 In response to a query from a father wanting joint programming tutorials with his son that appeared on the Chicago Python User Group (ChiPy; pronounced "chippie") mailing list, I volunteered to teach an introductory class in Python to all comers. I announced this on the ChiPy list and on the Linux Users of Northern Illinois (LUNI) list, and made no other effort to promote it. My colleague Andy Harrington, a professor at Loyola University of Chicago was able to arrange for a classroom for a Staurday afternoon. We met last weekend, and it went pretty well. In addition to another ChiPy volunteer, Robert Ramsdell, and Andy, over a dozen people showed up, three women, two fathers with young sons in tow, and about ten guys, all seriously motivated. After talking for too long, I walked them through some very simple exercises with the interactive prompt. We got as far as writing loops to draw a diamond figure in ASCII graphics. A few people managed to draw the whole kite figure which was my objective. You can see the slides I showed up with at http://webpages.luc.edu/~mt/pyfl/pyfl.html If I had it to do over, I'd just "dive in" (to coin a phrase) and skip the preamble, which I think was mostly a mistake. This was my first experience teaching complete beginners, and it will be helpful to me in preparation for my formally teaching an introductory CS course at Loyola this summer. I think most of the participants found it worthwhile as well. Probably the most interesting thing is we did almost zero promotion to fill the room. Just an announcement on the ChiPy list and an announcement on the Linux Users of Northern Illinois list. This leads me to suspect that you could pull this together in a smaller city, if you promoted it harder. There are people out there who want to learn Python. We should reach out to them. regards Michael Tobis _______________________________________________ marketing-python mailing list marketing-python(a)wingware.com http://wingware.com/mailman/listinfo/marketing-python ------- End of Forwarded Message

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How to Think Like A Computer Scientist
by Arthur 28 Mar '06

28 Mar '06

Ironically, apropos of the recent discussion How to Think Like A Computer Scientist - Java Version introduces the fundamental concepts of Object Oriented Programming by way of the creation of a mutable complex number. http://www.ibiblio.org/obp/thinkCSjav/chap13.htm FWIW. Art

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Python Workshop at Chapman University, Orange, CA, June 19-22, 2006
by Atanas Radenski 25 Mar '06

25 Mar '06

Dear edu-sig members, This email is to announce a summer workshop entitled "Python First: A Lab-Based Digital Introduction to Computer Science": http://www.chapman.edu/wcls/MathCS/sWorkshop/Python/default.asp This tuition-free workshop will be held on the Chapman University's campus in Orange, California, June 19-22 (Monday - Thursday). The workshop is intended for computer science educators who seek an alternative to either purely commercial languages, such as Java or C++, or educational languages, such as Scheme, for introductory computer science courses. The workshop will introduce participants to interactive program design with the Python programming language. Participants will also learn how to customize and manage a 'Python First' digital study pack. Daily activities will start with overview lectures and will continue with hands-on sessions in the computer lab. The summer workshop and all supporting materials are free. A nominal registration fee will cover meals and snacks. Transportation costs and lodging are the responsibility of the attendee. Please see: http://www.chapman.edu/wcls/MathCS/sWorkshop/Python/default.asp for complete details on the Python workshop and an on-line registration form. Or contact Dr. Arnold Shugarman (Shugarman(a)chapman.edu) for more information. Respectfully, Atanas Radenski mailto:radenski@chapman.edu http://www.chapman.edu/~radenski/

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FW: Properties use case
by Arthur 25 Mar '06

25 Mar '06

My response to something Grégoire sent me this off-list is below. My off-list response to him bounced. I see no reason why he would mind me posted it up so I take the liberty to do so. Apologies if Grégoire feels otherwise. Not something I generally like to do, but see no reason in this case why he would be all sensitive to it. Art > >-----Original Message----- > >From: Arthur [mailto:ajsiegel@optonline.com] > >Sent: Saturday, March 25, 2006 10:29 AM > >To: 'Grégoire Dooms'; 'Arthur' > >Subject: RE: [Edu-sig] Properties use case > > > > > > > >> >-----Original Message----- > >> >From: Grégoire Dooms [mailto:dooms@info.ucl.ac.be] > >> >> > >> >What is the question you ask here ? Do you want a > >certification that > >> >you have done your PyGeo The Right Way (tm) ? > > > >No. I see no issues and have some confidence in my overall > >design. People with more depth on some of these issues than > >I seem to be concerned that I am overconfident. I am simply > >trying to understand better why. > > > >*I* raised none of these questions. I raised what I > >understood to be a very specific, and - yes - technical > >issue about Numeric's typing mechanism. *I think* that *if* > >Numeric were to accept my custom type as a pseudo-complex > >type rather than something as general as a Python object, > >and processed it *as if* it were equivalent to a Python > >complex primitive, no harm would come to the calculations > >being performed and my ideas for the design I am pursuing, > >and am generally comfortable with, would proceed in an > >optimal manner. I am not *sure* that this is true. But even > >that question is not the question I raised. I was simply > >hoping to get far enough to be able to get some sense of > >whether it is true. I would be curious to learn why it is > >not, if it is not. But have no way of learning that if it > >is not even implementable. > > > >My question whether was and is - Is anyone aware, or > >could imagine, a mechanism that would allow me to coerce > >Numeric to process my custom type as a complex primitive > >while maintaining object identity? > > > >I have taken the silence as a *no*, a not terribly > >surprising *no*, and have begun to think about the > >implications of that *no* on my overall thinking about my > >overall design. > > > >I take reasonability for my design, but feel it not > >responsible to look-the-other-way when folks more > >experienced than I seem to have reasons to doubt its > >integrity - from the little I have said about it. Doubts > >have been raised and I am not looking-other-other-way. > > > >> >How do you store the dependency graph ? Is it cycle free (a > >> >DAG) ? How do you decide which objects need to be > >repainted when an > >> >other object is changed ? What is the overall design of the > >> >application ? > > > >Other then not knowing what a DAG is, I feel that the other > >issues you raise are under control in some reasonable way. > >Part of the Fun (tm) of doing PyGeo has been not just to > >find my way to solutions - first I needed to find my way to > >the issues. Eventually the issues seem to identify > >themselves, and in general the one's you raise have done so. > > > >Nothing yet (before these discussions) raised to me the > >issue of the thread safety of my geometric objects. > >Therefore I have not considered it to be an issue. > > > >I call the style in which I have approached the development > >of PyGeo - tongue-in-cheek - Naïve Programming. It's been a > >fascinating experience. > > > >But I am sincerely trying to inquire whether there could be > >something fundamental I have missed by this approach - only > >because the issue has been raised - presumably sincerely - > >by others. Perhaps it is so subtle as to be unidentifiable > >except under Extreme Circumstances (tm). Perhaps it doesn't exist. > > > >> >> No I do not lock my circle. > >> >> > >> >Do you use threads ? > > > >In one sense, and it depends. > > > >There is the *option* of running a TK control panel that > >provides functioning to control more aspects of the > >interactivity with the rendering window than can be > >controlled directly from the rendering window itself. These > >are more in the nature of changing some global settings > >on-the-fly, then they are about interactivity with the > >rendering and interactivity on a micro-second by > >micro-second basis - which, whether the control panel option > >is or is not selected - run together in one thread. In my > >conception of what is taking place, at least. > > > >Thanks for your interest in my question/dilemma. > > > >> >Best, > >> >-- > >> >Grégoire > >> > > >> >

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Re: [Edu-sig] Properties use case
by Laura Creighton 25 Mar '06

25 Mar '06

In a message of Sat, 25 Mar 2006 03:02:31 EST, Arthur writes: >It doesn't matter to me any more than whether my tax calculations are >consistently correct were my class the one you described a few posts back >. > >I think I should perhaps appreciate that Kirby is the only one talking >straight to me. This programming business is quite over-my-head. > >Art Ok, so it does matter. Are you locking your complex number before modifying it? Laura

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Re: [Edu-sig] Properties use case
by Laura Creighton 25 Mar '06

25 Mar '06

In a message of Thu, 23 Mar 2006 10:49:41 CST, "Michael Tobis" writes: >> Then it is the language implementor's headache to make the locking mec >hanism work. > >"from threading import Lock" > >generally works for me. > >Arthur is not implementing a general purpose thread-safe language, so >like him I continue to be confused as to the relevance of this >conversation to his project. > >This conversation has indeed been interesting. In particular I >appreciate the explanation of what Oz is about. However, one should >make clear whether one is musing or offering advice. > >It's my impression that the advice now boils down either to None, or >to abandon Python for Oz, neither of which is very helpful. Did I miss >something? Yes. from threading import Lock relies on the global interpreter lock to work. PyPy doesn't have one. It has never been clear to me whether Arthur has been locking his complex numbers before be modifies them or not, which is why I asked him 'should I worry' a while ago. It has also not been clear to me whether he _cares_ if he uses a half-modified complex number in the course of running things. Maybe for his purposes this doesn't matter. However, if it matters, and if he is using the global interpreter lock to keep problems from happening, then when he moves to a pure pypy solution, one of the changes in his way of thinking will have to be 'how to write this in the absence of the global interpreter lock'. Laura > >mt

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Re: [Edu-sig] Properties use case
by Laura Creighton 23 Mar '06

23 Mar '06

In a message of Thu, 23 Mar 2006 16:24:39 +0100, Grégoire Dooms writes: >Arthur wrote: >> >> >> >>>> -----Original Message----- >>>> From: Laura Creighton [mailto:lac@strakt.com] >>>> >> >> >>>> And I think he will like tens of thousands of threads, too, >>>> though if these just means tens of thousands of chances to >>>> modify only part of your complex number, when you wanted an >>>> atomic action guaranteed to modify both parts as one, then >>>> he may hate it before he likes it. :-) >>>> >> >> Sorry - I suspect everyone else is quite done with this, but I'm still >> bothered by mixed signals. >> >> I would like to be able to present PyGeo as good, sensible code. Not M >useum >> Quality, to be sure. But good and responsible. >> >> There is an implication in what you are saying that I am still off the >mark. >> Perhaps I am. But its not fair, in my mind, to throw that at me knowin >g >> that it still has not gotten through to me (and Zelle ?) in what way I >am >> off the mark. >> >> For the life of me I don't see the problem. My class has 2 __slots__ - >> .real and .imag. It does with them the kind of things that classes do. > >> >> How is this class different and less thread safe than an infinite numbe >r of >> other classes that do with attributes the kinds of things that classes >do >> with attributes? >> >This is a complex matter and I'll try to give a very short (hence a >little categoric) answer. >First of all, IMO Laura was referring to several thousands of >lightweight thread such as those found in the Oz/Mozart language >(http://www.mozart-oz.org). And that is because we have had a PyPy/Oz >sprint two weeks ago where we made plans and prototypes for the >integration of some ideas of Mozart into PyPy (mostly logic variables, >"search", and constraint programming, micro-threads were already on the g >o). > >In that language stateful datatypes such as mutable objects are an >exception. >By default the variable store is a single assignment store. That means >when you create a variable (e.g. with this statement X=_ ) it is >uninitialized (called unbound). Then when you assign it you cannot >rebind it to an other value: X=4 works but if you do X=5 later you get a >sort of exception (failure). In a sense = does not do assignment but >true mathematical equality (called unification). So you can do 4=X as >well as 1+X = 5. >The language supports very lightweight threads (having a million of >those is no problem), when they try to "use" the value of a variable , >they block if the variable is unbound. So you can launch >inter-dependant threads accessing values computed by each others without >wondering about the synchronization. That is called dataflow concurrency. > >In a sense, your mutable complex object is opposite to that approach >where (almost) all variables never ever change their value. >> I have unintentionally stimulated a CS nerve, apparently. But would s >till >> love to get to the bottom of issue. >> >HTH :-) >> Or get an official CS - proper use case aside - bill of health. >> >I would refer you to the CTM book: >http://www2.info.ucl.ac.be/people/PVR/book.html >You will find there lots of interresting ideas about computer language >semantics. > > >Best, >-- >Grégoire Dooms > >_______________________________________________ >Edu-sig mailing list >Edu-sig(a)python.org >http://mail.python.org/mailman/listinfo/edu-sig Thank you Grégoire for writing that. Much better than I could. Arthur, classes are not safe either. Say you have class that has two attributes, myclass.price and myclass.tax, and an update method that first assigns a new value to the price, and then, sometime later, even the very next line, assigns tax to be 7% of the price, unless the tax is over 300,000 in which case the tax is 300,000 very simple. And if you only have 1 thread, you are guaranteed that nobody is going to get a hold of an instance of myclass where the price has been changed, but that tax hasn't yet. Only one thing gets to run at all, so there is nobody else, to get a hold of things. Now add threading. Ooops, one thread could be using an instance while the other was updating it. Very bad for you. You need a way to lock' the object and say 'nobody gets to use this thing until I am done with it'. You can implement your own locking mechanism. Or you could use a language type that comes with the language -- a tuple, for instance -- which guarantees this atomicity you want. Then it is the language implementor's headache to make the locking mechanism work. Laura

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