Mailman 3 June 2015 - Edu-sig

a short essay about programming
by kirby urner 08 Dec '22

08 Dec '22

A common "error" (not too serious) that I see in beginning Python (and no doubt other languages, but Python is the one I'm teaching), is having a while condition that appears to put a lid on things, but then the flow all leaks away through break statements, such that the "front door" condition is never revisited. while guess != secret: guess = int(input("Guess?: ") if guess == secret: print("You guessed it!") break else: print("Nope, try again...") What's messed up about the above code is you never really go back to the top in the case where you'd get to leave. Rather, you exit by the back door, through break. So in that case, wouldn't have been simpler and more elegant, even more "correct" (dare I say it) to have gone: while True: # no ifs ands or buts guess = int(input("Guess?: ") if guess == secret: print("You guessed it!") break else: print("Nope, try again...") I see lots of heads nodding, and that could be the end of the matter, but then a next question arises: wouldn't this also be a more correct solution?: while guess != secret: guess = int(input("Guess?: ") if guess == secret: print("You guessed it!") continue # instead of break else: print("Nope, try again...") We're back to having a variable while condition, not a boolean constant, but this time we actually exit by means of it, thanks to continue or... while guess != secret: guess = int(input("Guess?: ") if guess == secret: print("You guessed it!") else: print("Nope, try again...") ... thanks to no continue. This last one is getting a thumbs up, but then I'd pause here and say "continue" can be easier on the eyes. It's unambiguous where it takes you, in contrast to having to scan on down the gauntlet, looking for possibly other open doors. "What happens next" should not require scanning ahead too far. Help us not to get lost. Be a civic-minded coder. I'm thinking of a programming style that advises two things: (a) if you use a while condition that's variable, that's expected to change, then your goal should be to always exit because of that, i.e. that should be your only exit point. Even if some other criterion suggests exiting, you have the option to flip that "lid" at the top, to crack that front door, and bounce the ball out. (b) which is why 'continue' is your friend. You are showing the user where your 'break' statements are, except you don't use "break" statements, as you've given a non-constant condition, and your aim is to make that your ONLY exit point. In short: never use break to exit a while loop unless your condition is while True. Instead, always flip the condition and exit through the font door. However, as soon as I make that rule I can think of good reasons to break it. The other programmers in the room are shaking their heads. Won't we lose information, needed elsewhere in the program, if we "artificially" force a True condition to False. Aren't we, in effect, lying? That concern could be addressed. Keep all the info true, just treat the "lid condition" (it "keeps a lid on it") as a flag. Go ahead and remember the user's guess. allowed = 5 tries = 1 exit = False while not exit: # no other way out guess = int(input("Guess?: ") if guess == secret: print("You guessed it!") exit = True # instead of break continue print("Nope, try again...") tries += 1 if tries == allowed: print("You've maxed out") exit = True continue I think we all understand the main issue: writing reader-friendly code, and rules for doing so. There's something comforting about approaching a while loop and knowing its not a leaky sieve, riddled with back doors, maybe even an exit( ) time bomb. But in the recursion world we want a minimum of two exits usually: when another round is called for versus when we've "hit bottom". Can we have it both ways? Conclusions: Lets not be too hasty with rules of thumb and: Lets keep the reader in mind when writing code. Just because the interpreter knows to compute the flow unambiguously, doesn't mean all ways of writing it are equally reader-friendly. What may seem a gratuitous gesture, an unnecessary flourish, may actually promote reader comprehension of your code, and that should be a goal as much as satisfying the interpreter. Kirby

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turtle coordinates: Y increase downards - as in most graphics API?
by Jurgis Pralgauskis 02 Jul '18

02 Jul '18

Hi, usually in computer graphics Y is counted to increase downwards. I casn do it with: setworldcoordinates(0, 400, 600, 0) but then, "right(..)" turns to the left :/ I could swap: right, left = left, right but on errror I get a bit misleading message >>> right() Traceback (most recent call last): File "<pyshell#10>", line 1, in <module> right() TypeError: left() takes exactly 1 argument (0 given) I thought to make this hack for kids, so better clearer error msgs... Any Ideas? Thanks :) -- Jurgis Pralgauskis tel: 8-616 77613; Don't worry, be happy and make things better ;) http://galvosukykla.lt

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a Mandelbrot Set in a few lines of Python
by Kirby Urner 23 Jun '15

23 Jun '15

I'm pleased how little code is required to make a decent Mandelbrot Set image using Numpy + PIL, neither of which am I expert at using. This is how one learns. :-D Here's how it looks on my screen: https://flic.kr/p/uR81qU For more about using fractals in teaching: Fractals, Graphics, and Mathematics Education, edited by Michael Frame and Benoit B. Mandelbrot (c) 2002, Mathematical Association of America ISBN: 0-88385-169-5 ==== ''' Produces a decently high rez b/w graphic of Mandelbrot Set in under a minute using default parameters. Not super fast, but conceptually useful both for the mathematics and for the demo of numpy + PIL in an I-Python Notebook. (cl) Kirby Urner, MIT License, 2015 Pilot study for O'Reilly School of Technology Using I-Python Notebook + pillow (PIL fork) + in Anaconda distro ''' from PIL import Image import numpy as np def setup(pixels=(3200,2400), offset=(-2.5, 1.2), inc=1/1000): ''' Create patch of complex plane c for z = z**2 + c itereactions pixels(columns, rows), offset(left, top), inc = step ''' x, y = pixels offx, offy = offset field = np.zeros((x, y)).astype(np.complex) for j in range(y): for i in range(x): field[i][j] = complex( offx + inc * i, offy - inc * j) return field def mandelbrot_set(c): ''' Apply Mandelbrot transform (orbit of 0) to c ''' z = np.zeros(c.shape).astype(np.complex) # starts 0s for idx in range(100): z = z * z + c idx = abs(z) >= 2 # continue weeding out z[idx] = 3+0j # stamp out-of-bounds with 3 newf = (abs(z) < 2).astype(np.ubyte) # keep those in set newf = newf * 255 # turn them white im = Image.fromarray(newf) im = im.rotate(90) return im m = setup() image = mandelbrot_set(m) # may take 30 seconds or more! image.save('mandelbrot.png', "png") image.show()

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Python5 @ OST / HK (science fiction)
by Kirby Urner 13 Jun '15

13 Jun '15

I've actually written some code for Python5 and it's a work in progress. Tractors instead of Turtles but as a way of introducing Turtles i.e. I'm not "anti-Turtle" in using a Tractor instead. A subclass of Tractor, CropCircleTractor, outputs the Mandelbrot Set. ASCII art output in version one, swapping in better graphics (deeper bit-wells) as the course progresses. OST = O'Reilly School of Technology, a real place, a real school. I work there, have for some years. HK = Hong Kong We don't have an OST in Hong Kong but the idea is "how would we design the parent classes of the current OST such that instances would work in other places." You could say i18n is the theme, and that's a pretty steady note for me (was our theme at the OSCON booth last year -- if you came by, our main guy was speaking in like Japanese, Portuguese etc., gifted in that way (me not so much)). No booth this year, but one of my co-workers is giving a talk. Looking forward! Dunno if 'A Pattern Language' is used much in CS. Sounds like an elementary patterns text but it's for architects mostly and deals with architectural "places" that crop up over and over: the nook, the hallway, the stairwell... like in movies; we can conjure myriad scenes (the tower, the basement...). I'm sketching OST / HK in terms of such Places at first: Oasis; Cruise; Stable... We have a stable of mentors in HK and through our "travel agency" (aka student services, like Expedia) you book a "cruise" (just a metaphor usually -- though in HK we might do some ships...). You being a student. Mentors from the stable come to the Oasis (aka watering hole) to fill up on courses (what caseload they'd like for the summer). Some mentors are lifers, others jump off and on more. We have celebrity guests. So that's pretty much what we have today, but a bare bones version. My in-house memos flesh it out more and explain how, in a parent class implementation, we can get more generalized about our Places and not get locked in to accidental features (attributes) of the current instance. That's a brainstorming technique other companies might already use I don't know. Yes, those "real world exigencies" matter, but in science fiction they don't so much. Kirby Python Mentor / OST

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ATTENTION! Education track now open!
by Nicholas H.Tollervey 10 Jun '15

10 Jun '15

Hi Folks, A quick heads up: today we're announcing the fourth annual PyCon UK education track today. Details can be found here: http://www.pyconuk.org/education/ Register here: http://www.pyconuk.org/register/ Are you a teacher? Do you know any teachers..? Teacher's continuing professional development day is on Friday 18th September. Thanks to the generous sponsorship of Bank of America (again) it only costs £50 for a teacher's conference ticket (not including conference meal). Can't get time off school? Not a problem - we (literally) have you covered: we have £200 bursaries for schools who send teachers so they can recover the cost of a supply teacher. We'll provide details for how to obtain the bursary when you attend the conference. Who's taking part? The Raspberry Pi Foundation education team, Jam Packed, teaching colleagues and professional Python programmers will all be contributing workshops. You'll also get a chance to mix and collaborate with the wider conference attended by the UK's most talented Python developers. The kids' day will be on Saturday 19th September. We aim to run various workshops aimed at young beginner Pythonistas throughout the day. These will include web design, robotics, Minecraft and physical computing. Our aim is to turn excited kids into exhausted but inspired proto-programmers. The cost is only £5 per child and parents/guardians get in for free. Lunch will be provided. You only need to bring an open mind and a sense of adventure! Spread the word, tell your friends and book tickets here: http://www.pyconuk.org/register/ I'm always happy to answer any questions you may have! Best wishes, Nicholas.

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fun with voting (by secret ballot)
by kirby urner 09 Jun '15

09 Jun '15

""" The code below derives from a thread on elections-wg(a)python.org where we were talking about tie-breaking techniques. There's a well known way that's actually used, but I was inspired to think about a game wherein the ballots are like playing cards in some ways, each encoded with a unique prime. I've got some notes in the moderator queue at math-teach (lots of traffic), for which I'll share the URL. More in this month's elections-wg archive, public-facing. It's just another way to introduce the Fundamental Theorem of Arithmetic while reminding students of the composite vs. prime distinction. Standard fare. (CL) copyleft, K. Urner / 4Dsolutions.net, 2015 """ import random class Ballot: """secret: unique prime belongs to ballot itself """ def __init__(self): self.dna = random.choice(pool_of_primes) # this is done at the store pool_of_primes.remove(self.dna) def vote(self, name, vote=1): self.candidate = name self.approve = vote def __repr__(self): return "Ballot with prime {}".format(self.dna) pool_of_primes = [int(it) for it in """\ 2 3 5 7 11 13 17 19 23 29 31 37 41 43 47 53 59 61 67 71 73 79 83 89 97 101 103 107 109 113 127 131 137 139 149 151 157 163 167 173 179 181 191 193 197 199 211 223 227 229 233 239""".split()] # 52 in a deck in this example deck = [Ballot() for _ in range(52)] # two extra ballots were not used random.shuffle(deck) # dealt to voters (how many they get depends on how many candidates) # ballots coming in from voters all over the world!.... # each candidate on the slate gates same number of ballots cast stackA = [] for _ in range(26): secret_ballot = deck.pop() secret_ballot.vote("Shrek") stackA.append(secret_ballot) stackB = [] for _ in range(26): secret_ballot = deck.pop() secret_ballot.vote("Alice") stackB.append(secret_ballot) # the Vote! a TIE, 25 for each candidate! def break_tie(sA, sB): productA, productB = 1, 1 for idx in range(len(sA)): productA = productA * sA[idx].dna productB = productB * sB[idx].dna if productA == productB: print("The impossible happened") raise Exception if productA > productB: print("Shrek wins!") else: print("Alice wins!") break_tie(stackA, stackB) print("The crowd roars")

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Congratulations to Mark Hammond
by kirby urner 09 Jun '15

09 Jun '15

10 June 2015 at 03:39, Brian Curtin: > It is my pleasure to announce that Mark Hammond has been chosen to > receive our Distinguished Service Award for his hugely impactful > contributions to Python on Windows. Through his contributions to > CPython and via pywin32, Windows would not be the platform it is > without a lot of his efforts. That was a common enough thought that > several releases in the 2.x series of Windows installers included a > special thanks to him. Congratulations! I've benefited a lot from Mark's work myself. Just having Python go so deeply in Windows helped make it the household name it is today. Kirby

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Distance Learning: where and how
by kirby urner 06 Jun '15

06 Jun '15

I take a debate-encouraging position against the standard cohort-based, curve- and letter-graded style of teaching in this blog post from when I was the USDLA (distance learning) conference: http://worldgame.blogspot.com/2015/04/against-grain.html But we have more in common than what divides us, as distance learning schools, I'm thinking. Especially those of us coming in from outside, experimental and unaccredited (but what's to stop Michigan from offering math credit to a high schooler taking our Python sequence? -- nothing but red tape?). This article is making the rounds a work today: http://www.bloomberg.com/news/articles/2015-05-07/coding-classes-attract-co… More discussion on python-cuba: https://mail.python.org/pipermail/python-cuba/2015-May/000037.html Kirby

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Re: [Edu-sig] Edu-sig Digest, Vol 143, Issue 4
by Marianne McKenna 05 Jun '15

05 Jun '15

I am away from the office today June 3rd. I will try to respond by email. If you need immediate help, please contact tech support. Thanks!

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Re: [Edu-sig] Edu-sig Digest, Vol 143, Issue 3
by Marianne McKenna 04 Jun '15

04 Jun '15

I am away from the office today June 3rd. I will try to respond by email. If you need immediate help, please contact tech support. Thanks!

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