Mailman 3 February 2017 - 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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MineCraft with Python
by Jurgis Pralgauskis 04 Dec '22

04 Dec '22

Hi, intro: many kids like MineCraft :) probably you know/heared of MineCraft Pi https://www.raspberrypi.org/learning/getting-started-with-minecraft-pi/ But there seems to be Py for real MC http://coderdojotc.readthedocs.io/projects/python-minecraft/en/latest/ http://www.instructables.com/id/Python-coding-for-Minecraft/ PS.: a nice article (from js4MC world) https://github.com/walterhiggins/ScriptCraft/blob/master/docs/YoungPersonsG… -- Jurgis Pralgauskis tel: 8-616 77613; Don't worry, be happy and make things better ;) http://galvosukykla.lt

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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 Triangle class (using @property)
by kirby urner 20 Feb '17

20 Feb '17

Regarding @property and covarying the dimensions of geometric shapes (Circle an example), I mentioned wanting to have a Triangle type for my middle school kids. The cloud-base Web browser based Codesters implementation of Python 3 is a dialect. No yield nor could I get @property to work, so made edges be method calls. https://www.codesters.com/preview/aaae86e39e61413b938ce3e5350515ca/ https://flic.kr/p/S86M6F (input console, triangle edges, area printed) https://flic.kr/p/S86Mfi (turtle graphics also drawn, behind the console) This Codesters version is a pared down full-blown 3.5 implementation on Github. https://github.com/4dsolutions/Python5/blob/master/triangles.py I'm not yet being as ambitious as I could be, defining rules for letting the user vary dimensions arbitrarily e.g. (1) change in area: resize to a similar triangle keeping all angles unchanged (2) change in edge: keep other two edges same length varying only opposite angle unless not possible, raise exception (3) change in angle: change opposite edge Given assignment to attributes (properties), the expectation is more "state change" of an object, versus obtaining a new immutable, as with strings. We're not calling, we're setting, the antithesis of the functional programming ideal, surrendering to objects with hidden state. In this implementation, I'm going with more of a read-only triangle. The initializer passes in vertexes A, B and C as (x,y) pairs and everything from then on is read-only. [2] The emphasis might be on learning about triangles, leveraging prior knowledge of Python syntax, or on leveraging prior knowledge about triangles to learn more about how to program in Python. I think it's a two way street. [3] Kirby PS: This thread over on math-teach is perking along.... http://mathforum.org/kb/thread.jspa?threadID=2838432 (expressing skepticism we can build competence through robot schools) [1] I first learned of Gattegno from Ian Benson at Pycon / Chicago the last year it was there, with connections to Stanford, including to Terry Winograd who knows Fernando Flores whom we had a Pycon 2016 keynote about as some might recall: https://youtu.be/ckW1xuGVpug?t=32m17s https://en.wikipedia.org/wiki/Terry_Winograd https://en.wikipedia.org/wiki/Fernando_Flores [2] Using __mul__ to implement scaling, returning a new Triangle, would make sense. That wouldn't be a state changer. [3] recycling my math teacher's lament (not quite the same as Lockhart's, though overlapping): https://medium.com/@kirbyurner/the-plight-of-high-school-math-teachers-c0fa… http://www.maa.org/external_archive/devlin/LockhartsLament.pdf

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Prime Numbers...
by kirby urner 19 Feb '17

19 Feb '17

I have this segment in my Python course (which I wrote, see below) where I show prime number generator using an iterator written in two ways: as a generator function and as a class. Just for kicks, I cut and pasted the code to Codesters and discovered that, while it replicates Python3 syntax, it's not yet a complete implementation of the language. yield and next are not supported keyword and builtin respectively. No problem, I put in a workaround. http://mybizmo.blogspot.com/2017/02/prime-numbers.html (screen shots) https://www.codesters.com/preview/4183156df3fa49e1b12a4ab206d280af/ (runnable) I had my 5th-8th graders run the code having discovered the concept of "prime number" was already familiar. I threw out some numbers asking if they were prime. The 8th grade girl was not fooled by 51. I sketched "trial by division" very briefly on the whiteboard but did not do any careful reading of the Python code, as at this age it's enough to just eyeball the stuff and realize it cuts and pastes. The 2nd example below actually produces 3000 primes, not 30, despite the comment. :-D Thanks to Wes for links, still following 'em. Kirby PS: we also use MIT Scratch in this class. I'm still somewhat on a learning curve with that one. I got it to work for a Martian Math segment: http://controlroom.blogspot.com/2016/12/more-core.html What's Martian Math? http://wikieducator.org/Martian_Math http://www.4dsolutions.net/satacad/martianmath/toc.html # -*- coding: utf-8 -*- """ Created on Mon Mar 14 14:40:53 2016 @author: Kirby Urner Create an iterable that gives back successive prime numbers in two different ways: as a class and as a generator function. Trial by division involves accumulating all primes so far and admitting new candidates to the club only if no prime up to the sqrt of same, divides with no remainder. """ class Primes: def __init__(self): self.candidate = 1 self._primes_so_far = [2] # first prime, only even prime def __iter__(self): """I'm already an iterator so just return me as is""" return self def __next__(self): """proof I'm an iterator""" while True: self.candidate += 2 # check odds only from now on for prev in self._primes_so_far: if prev**2 > self.candidate: self._primes_so_far.append(self.candidate) return self._primes_so_far[-2] if not divmod(self.candidate, prev)[1]: # no remainder! break def primes(): """generate successive prime numbers (trial by division)""" candidate = 1 _primes_so_far = [2] # first prime, only even prime yield _primes_so_far[-1] while True: candidate += 2 # check odds only from now on for prev in _primes_so_far: if prev**2 > candidate: yield candidate # surrender control at this point! _primes_so_far.append(candidate) break if not divmod(candidate, prev)[1]: # no remainder! break # done looping #p = Primes() # class based iterator #print([next(p) for _ in range(30)]) # next 30 primes please! p = primes() # generator function based iterator print([next(p) for _ in range(3000)]) # next 30 primes please!

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properties and geometric shapes
by kirby urner 18 Feb '17

18 Feb '17

Ya'll know about @property and some my remember a few months back I was sharing about a Circle type where you could change the radius, area, or perimeter, by simply assigning to these attributes, and the other two would magically co-vary. Likely many people have thought of that. Great way to teach / learn geometry. Like this: >>> c = Circle() >>> c.area = 50 >>> c.radius 3.989422804014327 >>> c.circumference = 5 >>> c.radius 0.7957747154594768 https://github.com/4dsolutions/Python5/blob/master/circle2.py I don't think a math teacher needs to painstakingly go through all the code before using this API. Go ahead and work with finished programs. We'll look at the source code by and by. The goal is to interact with the instances as modeling geometric shapes with co-varying dimensions. I haven't done a Triangle class that way yet. That'd be fun to do. Nor a Tetrahedron, in any generic way, though I have some components lying around. :-D Having only one dimension change at a time, leaving others free to co-vary, makes for a good study in ripple effects. I've recently co-developed, with David Koski, another specimen of geometric object with co-varying properties. It's called a TetraBook and visually consists of a triangular book meaning both front and back covers are equilateral triangles, all edges 2, with a shared hinge (the book's spine). Imagine this book flat open on its back, with a single triangular page wagging back and forth, another equilateral triangle of edges 2. When it's all the way to one side, flat against either cover, there's no volume to speak of. When the page turns, however, the segments from page tip to each cover tip define two complementary tetrahedrons, the turning page their common face. What the TetraBook instance is allows is I can assign any of five attributes and, thanks to property methods behind the scenes, the other four with co-vary. The angle of the page, the lengths of the tip-to-tip segments, the volumes of the complementary tetrahedrons (same), their altitudes (same). I can even assign volume in two different ways, depending on what I consider my unit of volume (regular tetrahedron or right tetrahedron, the latter corresponding to a cube volume of edges 1). On Github: https://github.com/4dsolutions/Python5/blob/master/tetrabook.py (has a couple dependencies, also there: qrays.py and tetravolume.py) I recommend this approach to other math teachers. If your school also has a computer science department, so much the better right? Kirby lambda calc track oregon curriculum network 4dsolutions.net/ocn https://www.youtube.com/channel/UCr7TZxfhsqbeiQzLnHdgPgA

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Scipy 2017 "Teen Track"
by Hearne, Mike 17 Feb '17

17 Feb '17

SciPy 2017, the sixteenth annual Scientific Computing with Python conference, will be held this July 10th-16th in Austin, Texas, at the AT&T Executive Education and Conference Center on the University of Texas campus. SciPy is a community dedicated to the advancement of scientific computing through open source Python software for mathematics, science, and engineering. The annual SciPy Conference allows participants from all types of organizations to showcase their latest projects, learn from skilled users and developers, and collaborate on code development. The Tutorial Committee is seeking an instructor for a new “Teen Track” tutorial, aimed at high-school students who have some experience with programming (if statements, for loops and the like) and an interest in science. We expect these students will be attending SciPy with parents or will be from local area high schools. There will be a $2000 stipend awarded to the instructor. Submissions can be emailed to SciPy(a)enthought.com, and details of the requirements for submission can be found in the attached Request for Proposal. Thanks, The Scipy 2017 Tutorial Committee

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dual use __main__: work or test
by kirby urner 14 Feb '17

14 Feb '17

Does anyone use this pattern?: (a) accept command line parameters if __name__ == "__main__" or (b) run unittests if no parameters passed Something like: if __name__ == "__main__": if len(sys.argv)==7: command_line() else: unittest.main() I'm using this pattern with my classes, as a way of touching on both passing arguments from the command line (with nod to argparse for POSIX compliance), and self-contained testing. Maybe this would be better with doctest instead. I could do another version.... Example: https://github.com/4dsolutions/Python5/blob/master/tetravolume.py Kirby

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Turtle
by Marcin Wojciechowski 12 Feb '17

12 Feb '17

Hello, I teach computer science in elementary school. Looking for information on turtle. I like very much and would like to apply it in the classroom. Marcin Wojciechowski http://marcinwojciechowski.edu.pl

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Re: [Edu-sig] update from Silicon Forest (follow-up)
by kirby urner 03 Feb '17

03 Feb '17

> > OK, back to my day. Codesters, then meetup with Steve Holden, former PSF > chairman and Pycon instigator (younger the EuroPython, that institution). > He's just breezing through PDX on a lark. First, apologies for my prior post of this month appearing twice in the archives, some kind of failure on my end, in the middle of a send, resulting in a double-send. As one of the listowners, I could mess with it and delete one, but why at this point? My main business is to report about having Steve Holden as my guest on my Python TV show (a small group of students taking advantage of a professional development opportunity). Steve and I had about 30 minutes to rehearse using Zoom.us to pass control of the desktop around. I switched to him for demonstrations of MicroPython controlling continuously variable speed propellor gizmos. We were on separate floors of the building, but one staircase apart. One the outgoing video feed, we were able to get us both side-by-side as talking heads, so that Steve could both hold up his circuit board [1] and share his MicroPython shell, running on the other end of a USB connection.[2] Later in the program he showed with the Wing IDE looks like. We mostly look at Spyder, not exclusively (at least PyCharm, Eclipse, and IDLE will likely appear). For those just joining us, Steve, former PSF chairman, lives in the UK but just happens to be in Portland, an old haunt of his.[3] Students were engaged and asked good questions. Kirby [1] https://flic.kr/p/QwrS84 (Pyboard, paper diagram) [2] https://flic.kr/p/RGD4Hb (USB connection to Pyboard, in turn controlling two servo-mechanisms) [3] http://worldgame.blogspot.com/2011/02/open-secrets.html (Steve making a splash when moving to Portland in 2011, my personal journal -- blog -- entry).

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