Mailman 3 October 2001 - Edu-sig

measuring python...
by Jeffrey Elkner 30 Nov '01

30 Nov '01

Hi All! I'm trying to get together a master's thesis and was hoping to do something related to Python's suitability as a language for teaching programming. I was thinking of comparing Python, C++, and Java solutions to common first year computer science problems in terms of length and readability. Comparing length is not a problem. "Readability" on the other hand is not easy to define in any quantifiable way. I was thinking of trying something like "tokens per line". Any thoughts? Thanks! jeff elkner yorktown high school arlington, va

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Re: [Edu-sig] How to Improve code performance
by Brent Burley 01 Nov '01

01 Nov '01

> Hi, > I am little obssessed with my own coded after i > found out it is slow. I am trying to construct a html > table string from a result that i obtain from > database.My code segment look like this: assume result > holds 2D list. > ******* method******************************** > def f1(item): > return "<td>"+str(item)+"</td>" > ***************************************** > ************main program piece*********** > tab = "<table align='center' border='1'>\n" > for x in result: > tab = tab + "<tr>" > tab = tab + string.join(map(f1,x),"")+"</tr>\n" > tab = tab + "</table>" > print "Content-type:text/html\n" > print tab > ********************************************** > Can anyone improve this code segment? Thanks alot The big problem is that tab=tab+"..." in a loop is expensive since Python must allocate a new string and copy the old one each time. The running time will increase with the square of the number of records, i.e. O(n*n). It may not be intuitive, but putting all the partial strings in a list and then joining them at the end is more efficient as the running time will increase only linearly with the number of records, i.e. O(n). tab = [] tab.append("<table align='center' border='1'>\n") for x in result: tab.append("<tr>") for y in x: tab.extend(("<td>",y,"</td>\n")) tab.append("</tr>") tab.append("</table>") print string.join(tab, "") O(n) will always beat O(n*2) for large enough n, even if the individual operations are slower. Brent

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Pybibliotheca
by Robert Rickenbrode II 31 Oct '01

31 Oct '01

Folks - somehow I missed this, but I just looked at PyBibliotheca at http://www.ibiblio.org/obp/. Very cool. Does anyone know if there are going to be mechanisms to submit lesson plans/programming projects/etc. to this repository? Thanks, Rob Robert K. Rickenbrode II rkr_ii(a)yahoo.com

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How to Improve code performance
by Titu Kim 30 Oct '01

30 Oct '01

Hi, I am little obssessed with my own coded after i found out it is slow. I am trying to construct a html table string from a result that i obtain from database.My code segment look like this: assume result holds 2D list. ******* method******************************** def f1(item): return "<td>"+str(item)+"</td>" ***************************************** ************main program piece*********** tab = "<table align='center' border='1'>\n" for x in result: tab = tab + "<tr>" tab = tab + string.join(map(f1,x),"")+"</tr>\n" tab = tab + "</table>" print "Content-type:text/html\n" print tab ********************************************** Can anyone improve this code segment? Thanks alot Regards, Kim Titu __________________________________________________ Do You Yahoo!? Make a great connection at Yahoo! Personals. http://personals.yahoo.com

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How to detect dst problem.
by Titu Kim 29 Oct '01

29 Oct '01

Hi, My program does not give correct time reading because of day light time saving happened over last weekend. I have to mannually add/subtract a -1 constant everytime this happens. Is there a way that i can detect dst change so this add/subtract can happen automatically? For instance, i can do an if statement to determine what constant should be added when computing a time value. Thanks a lot. Regards Kim Titu __________________________________________________ Do You Yahoo!? Make a great connection at Yahoo! Personals. http://personals.yahoo.com

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__init__ returning subclasses
by Jay Bloodworth 22 Oct '01

22 Oct '01

Hiya, This is really more a general programming question than a python-in-edu question, but it's related to project for education that I'm working on, and based on lurking for a while I'm pretty sure some members of the list will have some interest and expertise to answer. Say I have some class definitions like this: class Expression: stuff class LinearExpression(Expression): stuff class QuadraticExpression(Expression): stuff Is there any way to make the Expression constructor return an instance of one of the subclasses (based on its arguments) rather than an Expression instance. E.G. e=Expression("3x+5") e.__class__ == <class LinearExpression> e=Expression("x^2-9") e.__class__ == <class QuadraticExpression> I can think of plenty of workarounds involving helper functions and I can think of a number reason why idiom given above might not be The Right Thing whether or not it is possible. But I can't help thinking that there is an elegance to this approach: Let the superclass choose the appropiate subclass as an implementation, based on what it is supposed to represent. Similarly, can a class constructor choose not to construct a class and instead return a base type object? For example (assuming Fraction is a suitably designed class for rationals), can you do: f=Fraction(1,2) # Fraction(n,d) => n/d type(f) == <type 'instance'> f=Fraction(2,1) type(f) == <type 'int'> Again, I can think of reasons not to do this, but it seems reasonable to let the class pick the most appropriate implementation of itself as possible, and if that is a builtin type, why not? It's probably obvious from my examples that I'm interested in computer algebra. I've found a few python CA systems: fewer than I'd expect, more than I'd like to evaluate one by one, none well documented enough for me to guess how easy to use/featureful they are. Anybody got any advice/pointers for good, extensible computer algebra implementations under python? Thanks, Jay

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re: PyGeo presentation
by Arthur Siegel 20 Oct '01

20 Oct '01

Kirby - >Thanks for keeping us abreast of developments re Pygeo >in academia, Art. This has been a fun adventure on >which to keep tabs. A fun adventure indeed. Got an e-mail yesterday from one of the math professors who attended, telling me he enjoyed the presentation and the software and apologizing for not being able to join us afterward for dinner. Do a web search and find that he had co-authored some math articles with the guy who is the Director of the Institute for Advanced Studies at Princeton. Occurred to me that he was just being polite, but... Immediately walked over to David's house to let him know that I am too smart to be his friend anymore. In celebration I hope to post up the new improved PyGeo and see about getting the Edu-Sig page link properly pointed. Art

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Re: [Edu-sig] Thanks for the tip
by Chris Meyers 19 Oct '01

19 Oct '01

I would like to thank Jason for his recent recommedation of "Who is Fourier? A Mathematical Adventure" translated from Japanese by Alan Gleason. I bought a copy last week. The book is an absolute delight and should be read by both students interested in math/science and anyone *teaching* math or math-like subjects. For details read the reader reviews on amazon.com (it gets almost unanimous 5 star ratings). A friend has also ordered "What is Quantum Mechanics? A Physics Adventure" by the same folks. Looking forward to it. Thanks Chris

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re: PyGeo Presentation
by arthur.siegel＠rsmi.com 19 Oct '01

19 Oct '01

I had written - >Proud to note that I will be giving a presentation >of PyGeo to a portion of the math faculty/students >at PolyTechnic University in NY tomorrow evening. Great fun to have gotten the right audience - and some good feedback. They were great good sports in seeing the best in the efforts of an amateur - making up in passion for a "mission" what he may be lacking in technical depth. Except that the only non-departmental guest in the audience was a tech heavyweight with an interest in education and technology issues . Ironically, after my presentation I overheard him talking to the math department head,quoting Alan Kay - with whom he apparently enjoys some personal relationship. I mentioned I had heard he left Disney - and left it at that. (Since it was only the Disney connection that ever distrubed me.) Despite my track record with the Python establishment, I must say I thought I made an effective spokesman for the case of Python and related goodies - including PyGeo of course - as tools that quite well belong in a math department's arsenal. Art

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Re: PyCrust, IDLE
by Christian Mascher 17 Oct '01

17 Oct '01

> From: Kirby Urner <urnerk(a)qwest.net> > Subject: [Edu-sig] PyCrust > > One thing that's cool about IDLE is if I have > a multi-line function or class defined at the shell > prompt, I can scroll back and click on any of these > lines to get a full copy of the whole function or > class -- which I may now edit/revise. Having only > a single line copy down doesn't allow easy re-editing. > If I use copy/paste, I can get multiple lines, but > the interpreter seems to only recogize the last > one. I want to second this. When using python in the classroom, I've always used IDLE mostly because of this feature. I realized the importance of the "multi-line recall by cursor movement" when I installed a Python-shell on an old win3.1-laptop lately (no TK, no IDLE): editing is really no fun in shell mode, so I couldn't work with it as before which is about like this: Together with a beamer, we often start by using one IDLE-shell as an experimental interface, where one pupil can code an algorithm and test it directly, while the class can follow the interaction on the projected screen. Any occuring errors can be corrected by others, functions can be modified step by step in hardly any time. This is a very efficient way in working with a whole class. We seldom edit a file. In the case that we do, the process is slowed down by the distraction of having to save the file etc. In IDLE we stay focussed on building the function-algorithm. And we can play around a lot even in a classroom situation, because we don't have to type that much when we do a change. Afterwards pupils had little difficulty in using idle when doing problems on their own with a partner. I must confess I haven't tried out pycrust yet though it sounds promising. Christian

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