Mailman 3 May 2009 - Edu-sig

xturtle online via processing.js !?
by Jurgis Pralgauskis 27 Sep '12

27 Sep '12

Hi, I am struggling around with interactive online py tutorials with https://launchpad.net/projects/intro-to-code (ith might become securely sandboxed soon, as pypy made it possible http://blog.sandbox.lt/en/WSGI%20and%20PyPy%20sandbox :) but one more thing is I'd like to let access xturtle functionality online - one possible way could be triggering tkinter to save its canvas to ps, and then convert them with imagemagic and show via web (animated gif or static) - but if pyjamas can render GUI for js (http://www.google.lt/search?&q=pyjamas+python ), mayby there is a way to **translate turtle commands to processing.js analogues** http://ejohn.org/blog/processingjs/ would it be difficult -- how do you think? -- Jurgis Pralgauskis tel: 8-616 77613; jabber: jurgis(a)akl.lt; skype: dz0rdzas; Don't worry, be happy and make things better ;) http://sagemath.visiems.lt

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poking around in Py3k (recycling old algebra)
by kirby urner 28 May '09

28 May '09

The code below is somewhat boringly similar to other stuff I've archived here before, about finding all the totatives (defined below) of some N, then multiplying all possible pairs (a Cartesian product) modulo N to show how you've got closure i.e. you never get outside the group. The totatives of N are the numbers 1...(N-1) with no factors in common with N. If N is prime, every integer 1...(N-1) is a totative. The totient of N is *how many* totatives it has. Think how it'd only take you a few lessons to have your students impressing their guardians with stuff Euler talked about (make sure they pronounce "Euler" right). Hey, did you know Ellipsis is a new primitive object in Python 3, denoted ... ? >>> ... Ellipsis What's a little bit different in this pass is I'm applying some stuff I learned from Steve Holden @ Pycon re iterators, other subsequent trainings. Iterators are "one way streets" that become exhausted (dead end in StopIteration) so you might need to clone them ahead of time. The itertools tee is good for that e.g. lazyA, lazyB = itertools.tee( iteratorX ) will give you two for the price of one, then don't use iteratorX anymore (it's exhausted). Below, I want the totient (== number of totatives), so consume a whole iterator going totient = len(list(theiterator)) -- but fortunately I tee first. Hey, I was just learning from David Beazley on Safari that __repr__ is generally supposed to emit a string that'll eval right back to the object represented. So if I have Modulo type and go k = Modulo(10) then my __repr__ should maybe just emit 'Modulo(10)'. __str__ is for something prettier maybe (adding makeup). itertools.product will pair each with every, given two iterators (actually, takes any number, proceeds odometer style), but again, if you were to use the same iterator twice, you'd end up consuming all the rows so nothing left for columns or vice versa. That's where the repeat keyword argument comes in, which I use as an alternative to tee for a check (see multiply_a vs. multiply_b). Other little known features of Python 3.x, the ability to write: >>> def f(x:int) -> int: return x * x >>> f.__annotations__ {'x': <class 'int'>, 'return': <class 'int'>} The new __prepare__ method allowing processing in the classdict you're about to hand off to __new__, bolstering metaclass definitions. Set and dictionary comprehensions, cool. I play with a set comprehension below, limiting the output of the Cayley table to unique terms only (note curly braces in output) -- what takes the most room are the powering tables, where I take each totative t and go pow( t, e, N) with e ranging from 0 to totient-1 (a list comprehension). This relates to RSA. Also this is kinda weird (newly legal syntax): >>> alpha, *junk, omega = "This is sorta cool syntax eh?".split() >>> alpha 'This' >>> junk ['is', 'sorta', 'cool', 'syntax'] >>> omega 'eh?' >>> OK, the rest is source code, with output listed at the end... """ product does a cartesian product of two iterables tee replicates iterables 'repeat' times (default repeat=2) More of what this is actually about: http://www.4dsolutions.net/ocn/flash/group.html (yikes, evil noise! turn down those headphones!) """ from itertools import product, tee def gcd(a,b): """ EA per Guido """ while b: a, b = b, a % b return a def tots(n): """ returns iterator of no factors in common (totatives) """ return (i for i in range(n) if gcd(i, n) == 1) def multiply_a(ts,n): """ Cayley Table of ts x ts modulo n """ ps = product(ts, repeat=2) return (i*j % n for i,j in ps) def multiply_b(ts,n): """ Cayley Table of ts x ts modulo n (alternate implementation) """ row, col = tee(ts) ps = product(row, col) return (i*j % n for i,j in ps) def powers(ts,n): a,b = tee(ts) totient = len(list(b)) for t in a: print([pow(t,exp,n) for exp in range(totient)]) def test(n): print({i for i in multiply_a(tots(n),n)}) # print({i for i in multiply_b(tots(n),n)}) powers(tots(n),n) if __name__ == '__main__': test(12) test(15) test(21) test(24) So what's the printout if you run it?.... >>> ================================ RESTART ================================ >>> {1, 11, 5, 7} [1, 1, 1, 1] [1, 5, 1, 5] [1, 7, 1, 7] [1, 11, 1, 11] {1, 2, 4, 7, 8, 11, 13, 14} [1, 1, 1, 1, 1, 1, 1, 1] [1, 2, 4, 8, 1, 2, 4, 8] [1, 4, 1, 4, 1, 4, 1, 4] [1, 7, 4, 13, 1, 7, 4, 13] [1, 8, 4, 2, 1, 8, 4, 2] [1, 11, 1, 11, 1, 11, 1, 11] [1, 13, 4, 7, 1, 13, 4, 7] [1, 14, 1, 14, 1, 14, 1, 14] {1, 2, 4, 5, 8, 10, 11, 13, 16, 17, 19, 20} [1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1] [1, 2, 4, 8, 16, 11, 1, 2, 4, 8, 16, 11] [1, 4, 16, 1, 4, 16, 1, 4, 16, 1, 4, 16] [1, 5, 4, 20, 16, 17, 1, 5, 4, 20, 16, 17] [1, 8, 1, 8, 1, 8, 1, 8, 1, 8, 1, 8] [1, 10, 16, 13, 4, 19, 1, 10, 16, 13, 4, 19] [1, 11, 16, 8, 4, 2, 1, 11, 16, 8, 4, 2] [1, 13, 1, 13, 1, 13, 1, 13, 1, 13, 1, 13] [1, 16, 4, 1, 16, 4, 1, 16, 4, 1, 16, 4] [1, 17, 16, 20, 4, 5, 1, 17, 16, 20, 4, 5] [1, 19, 4, 13, 16, 10, 1, 19, 4, 13, 16, 10] [1, 20, 1, 20, 1, 20, 1, 20, 1, 20, 1, 20] {1, 5, 7, 11, 13, 17, 19, 23} [1, 1, 1, 1, 1, 1, 1, 1] [1, 5, 1, 5, 1, 5, 1, 5] [1, 7, 1, 7, 1, 7, 1, 7] [1, 11, 1, 11, 1, 11, 1, 11] [1, 13, 1, 13, 1, 13, 1, 13] [1, 17, 1, 17, 1, 17, 1, 17] [1, 19, 1, 19, 1, 19, 1, 19] [1, 23, 1, 23, 1, 23, 1, 23] >>> As I said, kinda boring maybe.... Kirby

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Re: [Edu-sig] Overloading (was Re: more on "variable names")
by Laura Creighton 27 May '09

27 May '09

I no longer think that the problem is that the '=' symbol is overloaded. I now believe that the problem is that when we, as teachers teach Python, we read a = b as 'a equals b' and if we forbid that language usage of the word equals, and always said 'a is bound to b' instead, then, in students who are learning their first programming language and don't come with C baggage, the problem will not arise, in much the same way that using * for multiplication does not cause a problem. So far this has worked, by my experiment has only been performed with 6 students so far -- hardly a large enough experiemental set. And the experiment is flawed because it is still quite difficult for me to stop saying 'equals', so I still use the forbidden words every so often. Telling the sudents they can point and make faces at me every time I slip up does wonders for improving me. Laura

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Re: [Edu-sig] Overloading (was Re: more on "variable names")
by Laura Creighton 27 May '09

27 May '09

p.s. Here is a test to see if your students understand about binding, or if they are walking around with it confused with equality. >>> class Animal: ... def __init__(eyecolour, sound, action): ... self.eyecolour = eyecolour ... self.sound = sound ... self.action = action ... >>> cat = Animal('green', 'miaux', 'pounce') >>> dog = Animal('brown', 'woof', 'wag') >>> vlerb = Animal('green', 'miaux', 'pounce') Now go ask them if what they think vlerb == cat will print. This is an easier place to clear up the misunderstanding than the first time they start passing mutable objects as defaults to a function or a method, which is where my classes in the past have tended to blow up with this sort of misunderstanding. Laura

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Simple Stats (curriculum fragment...)
by kirby urner 27 May '09

27 May '09

""" Simple randomizer and tally machine. Drop a ball 'howmany' times so it falls left or right for 'howmany' rows of pegs -- like Pachinko http://www.4dsolutions.net/ocn/graphics/randtrianim.gif (c) GPL, 4D OCN 2009 Python 3.0.1 (r301:69556, Mar 14 2009, 14:06:26) [GCC 4.2.4 (Ubuntu 4.2.4-1ubuntu3)] on linux2 """ from random import randint def leftright(): """ spit out L or R (left or right) until the cows come home """ while True: yield ['R','L'][randint(0,1)] def the_fall(howfar): """ drop from the top: go left or right for however far """ mypath = [] for i in range(howfar): mypath.append(next(y)) # using da generator return mypath def many_falls(howmany, howfar): """ dropping the ball, building a dictionary (sample) Order of Ls and Rs in a single fall leads to same final position, so index by string e.g. LLLLRRR """ counters = {} for i in range(howmany): thepath = "".join((sorted(the_fall(howfar)))) counters[thepath] = counters.setdefault(thepath,0) + 1 return counters def display(sample): """ spit out the fall strings in alpha order with associated counts """ thekeys = sorted(sample.keys()) for i in thekeys: print("%s : %4d" % (i, sample[i])) def test(): """ run a sample, display the results """ global y # so we can use it anywhere! y = leftright() sample = many_falls(10000, 10) display(sample) if __name__ == '__main__': test() ========== Multiple runs: >>> LLLLLLLLLL : 15 LLLLLLLLLR : 109 LLLLLLLLRR : 438 LLLLLLLRRR : 1205 LLLLLLRRRR : 1976 LLLLLRRRRR : 2491 LLLLRRRRRR : 2118 LLLRRRRRRR : 1138 LLRRRRRRRR : 416 LRRRRRRRRR : 84 RRRRRRRRRR : 10 >>> LLLLLLLLLL : 11 LLLLLLLLLR : 96 LLLLLLLLRR : 454 LLLLLLLRRR : 1144 LLLLLLRRRR : 2027 LLLLLRRRRR : 2444 LLLLRRRRRR : 2066 LLLRRRRRRR : 1194 LLRRRRRRRR : 443 LRRRRRRRRR : 111 RRRRRRRRRR : 10 >>>

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Overloading (was Re: more on "variable names")
by Edward Cherlin 27 May '09

27 May '09

On Sat, May 23, 2009 at 7:43 PM, kirby urner <kirby.urner(a)gmail.com> wrote: > I filed the following quick comment after viewing a six minute > tutorial on variables and values at ShowMeDo. > > The video: > > http://showmedo.com/videotutorials/video?name=6950010&fromSeriesID=695 > > My comment: > """ > idea that values are "stored into" a variable is less the metaphor in > Python, Yes, it is a relic of assembly language. A variable is not a section of memory. It is a pronoun which can have different referents at different times. One object can be referred to by many different personal names and a variety of pronouns at the same time. This is easier to explain in Japanese, which has numerous and ever-shifting sets of pronouns. "I" in English can currently correspond to o watashi o atashi o atai o boku o ore Historically, people could also have three, four, even a dozen personal names, some chosen for various private or public purposes, some awarded by teachers, some (rarely) awarded by the Emperor, and so on. > which is more about assigning or binding names to objects with > the assignment operator (=). The problem with "store into" is then > its hard to picture many names for the same object, yet that's easy > when you think of a balloon with many strings. > """ > For example, the so-called "equal sign" (=) would be better called an > "assignment operator" as most of us here do. We would do better to use a different symbol entirely. The only reason for the massive overloading practiced in conventional programming languages is the utterly obsolete ASCII character set. APL has used the left-pointing arrow '←' for assignment for decades, and treated '=' as a Boolean function returning a truth value. Just as APL has used the correct '×' and '÷' rather than overloading ASCII characters further. J distinguishes the function '=' from assignment '=.'. > To make this link stick we could explain how the two parallel lines > represent "opening a channel to" i.e. now this name (on the left) will > be able to communicate with the object on the right (some result of > evaluation). -1 > Kirby > > PS: do Python's where Prada? > http://fashionshops.wordpress.com/2009/05/18/prada-ad-campaign-ss-2009/ > _______________________________________________ > Edu-sig mailing list > Edu-sig(a)python.org > http://mail.python.org/mailman/listinfo/edu-sig -- Silent Thunder (默雷/धर्ममेघशब्दगर्ज/دھرممیگھشبدگر ج) is my name And Children are my nation. The Cosmos is my dwelling place, The Truth my destination. http://earthtreasury.org/worknet (Edward Mokurai Cherlin)

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F.Y.I.: this month's cover story for CACM is "OLPC: Vision vs. Reality" (cross posted)
by gerry_lowry (alliston ontario canada) 26 May '09

26 May '09

http://www.acm.org/ Regards, Gerry

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Re: [Edu-sig] Pythonic Math must include...
by Daniel Ajoy 26 May '09

26 May '09

I've some other candidates that I have included in my Logo Functional Extensions (LogoFE). * A function that receives a math function and plots it. * A function that receives a math equation and an interval and finds a root in that interval * A function that receives a math function and an interval and calculates the area under that curve * The Ruffini algorithm * A function that receives a math function and a X coordinate and finds the derivative at that point. Or returns the derivative function if you like. * Set arithmetic. Including set product. This, together with "join" and list comprehensions is all you need instead of SQL * Functions that produce permutations and combinations of a tuple. Daniel

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more on "variable names"
by kirby urner 24 May '09

24 May '09

I filed the following quick comment after viewing a six minute tutorial on variables and values at ShowMeDo. The video: http://showmedo.com/videotutorials/video?name=6950010&fromSeriesID=695 My comment: """ idea that values are "stored into" a variable is less the metaphor in Python, which is more about assigning or binding names to objects with the assignment operator (=). The problem with "store into" is then its hard to picture many names for the same object, yet that's easy when you think of a balloon with many strings. """ Yikes it posted three times dammit, makes me the foolish dweeb. Anyway, based on our longish threads here awhile back, I think "we who consider ourselves Python teachers" should actively check ourselves against using the verbs "to store in" or "store into" with respect to objects and their top-level names. The reason is, once you picture a dog in a doghouse, with the variable name as the doghouse, then it's hard to visualize how other doghouses could contain the same dog (the same value) without there being multiple copies of the same dog (clones?). A better image is balloons on strings. I realize it's not customary to have one helium balloon with two or more strings, different hands holding each string, sharing the same balloon, but there's nothing conceptually difficult about it (feels kind of ubuntu), whereas with that dog in the doghouse... that way madness lies. As several teaching professionals were noting on this list, a Python name is a lot more like a C pointer in the sense that it neither grows nor shrinks with respect to that which it names, i.e. the "size of object" is not a name's concern (another way to break the hold of the container-contained imagery). I think when we teach low level (including but not limited to children), we actually mess with (rewire) basic associations, a common technique in pedagogy (called "mnemonics"). For example, the so-called "equal sign" (=) would be better called an "assignment operator" as most of us here do. To make this link stick we could explain how the two parallel lines represent "opening a channel to" i.e. now this name (on the left) will be able to communicate with the object on the right (some result of evaluation). Why "open a channel to"? Because now we have "dot notation" i.e. our little API "control panel" at the near end of the string, our little "interface words" (triggers, attributes, methods with args)... our "messages" (to use Smalltalky talk). We don't really want s = 3 to be read "s equals 3" in Python. It's closer to "s names 3" or "s represents 3" or even "s speaks for 3". Not "s stores 3", nor "s contains 3". Probably the idea of "garbage collection" should be introduced right at this juncture, with arched eyebrows ala Spock if we forget to mention it. That's a really good way to anchor the many-to-one strings-to-balloon metaphor, with the idea of a reference counter on the object. Dogs in doghouses don't have reference counters, plus we wouldn't want them garbage collected. Balloons, on the other hand, go pop, which'd be a convenient way to represent "freeing up memory". Kirby PS: do Python's where Prada? http://fashionshops.wordpress.com/2009/05/18/prada-ad-campaign-ss-2009/

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eduPycon on conferences list (proposal)
by kirby urner 24 May '09

24 May '09

Some of you will maybe have seen David Goodger's announcement of a new Python community list focused on Python conferences: http://mail.python.org/mailman/listinfo/conferences I was hanging out at the virtual water cooler with PSF's Jeff Rush, mentioning his eduPycon idea, thinking we might have discussions on edu-sig, but maybe this new venue is more apropos? Here's our water cooler exchange in cyberspace FYI: http://mail.python.org/pipermail/portland/2009-May/date.html Kirby

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