Mailman 3 August 2013 - 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

8 17

Re: [Edu-sig] RurPLE-NG is nice
by Jurgis Pralgauskis 05 Apr '14

05 Apr '14

Some updates: - separated Variables Watch and Output panes, to be seen simultaneusly - implemented Breakpoints :) - beta style Todo: - let enter arbitrary watch expressions http://ftp.akl.lt/users/jurgis/python/rurple-NG053.png http://ftp.akl.lt/users/jurgis/python/rurple-ng-dz0-SplitLogVars_and_Breakp… for windows one doesn't need to install python separately, just unzip and run :) http://ftp.akl.lt/users/jurgis/python/RURPLE-NG-0.53%20%5bindependent%20exe… ps.: RurPLE-NG uses py3 unicode_literals, with_statement, division, print_function so code is generally py3 compliant. when wxpy will work well with py3 it shouldn't be too hard to port fully... >> >> just wanted to mention, >> that http://dev.lshift.net/paul/rurple/ >> is a very nice and lightweit PLE. >> >> what I like most (compared to RurPLE) are: >> 1) variables watch list (if it had breakpoints, it would rock :)

2 3

Easy Web Environment to post pupils Python Creations
by Philip Bagge 01 Apr '14

01 Apr '14

Dear Colleagues, My Y6 pupils (10-11 year olds) have been creating some simple text based linear adventures using Python. Does anyone know of a way we can play their adventures online? They are not very complicated. You can see the planning here. https://sites.google.com/site/pythoncodecouk/python-adventure Also as a new person to your forum does anyone know of an easy way to search you archives just in case someone has already answered this question. Thanks in advance for any help Phil Bagge -- Primary ICT Advanced Skills Teacher HCC Teacher & IT Manager http://code-it.co.uk

4 5

IPython shell + interactive program visualizations
by Philip Guo 31 Aug '13

31 Aug '13

Here's a one-minute video showing the latest extension to my Online Python Tutor project (http://pythontutor.com/). This feature is especially handy for teaching beginners on the interactive shell: http://www.youtube.com/watch?v=Q3oarDuZPL0

2 1

idea to use inspect for python quiz question generation
by Jurgis Pralgauskis 31 Aug '13

31 Aug '13

Hi, I want to make big question-base of basic algirthms' for CS101 and I thought how to describe them in Python https://code.google.com/p/algorithm-quiz/source/browse/IDEAS.draft.txt def's would be question templates and params would make the variations So the code would be pure Python (so easy to find/get examples ;) Now the headache is how to convert the py code to Moodle format? On each call of the question-def I want, to replace parameters in source with their values, and then to catch the output (as it is (usually) the answer) seems inspect + sys.settrace (on calls) could do? http://docs.python.org/3/library/inspect.html#inspect.getsource http://docs.python.org/3/library/inspect.html#inspect.getargvalues http://pymotw.com/2/sys/tracing.html and output could be catched probably http://coreygoldberg.blogspot.com/2009/05/python-redirect-or-turn-off-stdou… or via print redirect to file I am not much experienced with this area... Maybe Roberge or others could help - put on the right/best way? :) -- Jurgis Pralgauskis tel: 8-616 77613; Don't worry, be happy and make things better ;) http://galvosukykla.lt

1 0

the zip( ) function in Algebra 2?
by Kirby Urner 30 Aug '13

30 Aug '13

I make a big deal out of this Python fragment in a Math Forum essay I recently posted: >>> result = zip({"planet", "comet", "sun"}, {"paramecium", "duck", "aardvark"}, {"banana", "apple", "orange"}) >>> list(result) [('planet', 'aardvark', 'orange'), ('sun', 'paramecium', 'apple'), ('comet', 'duck', 'banana')] The indentation is artificial and in gmail the >>> lines are blue, because that's how the Math Forum archives treats it, but other than that, it's unadulterated cut 'n paste Python. What might drive a reader crazy is it looks like it should maybe pick "the next" element from each set to form its groupings, and it does, but then sets have no order, no ranking, no index. So even though "aardvark" is right-most in the set, it's the first picked. Python veterans get it right away and aren't phased, and we don't have Python to blame, are not assigning blame at all. This is pure math in an elementary form: sets have no "first or last" so don't expect sets to behave like lists or tuples. Python got it right, so no apologies. So how isn't this like "algebra" again? I went through it twice, as a student and as a teacher, and I can assure you, if "high school algebra" is important then "computer language in a console" is important. We knew that as long ago as the 1980s. I have other recent essays reminiscing, sharing analysis. There's lots to discuss, about why we didn't get there. Entry point to more writings: http://mathforum.org/kb/thread.jspa?threadID=2592483 Kirby

1 2

Fwd: CS Circles is open-source!
by Jurgis Pralgauskis 30 Aug '13

30 Aug '13

Worth attention!! very nice interactive Python course (software + content) opensourced! ---------- Forwarded message ---------- From: Computer Science Circles <cscircles(a)uwaterloo.ca> Date: Wed, Aug 28, 2013 at 8:26 PM Subject: CS Circles is open-source! To: jurgis.pralgauskis(a)gmail.com Dear CS Circles user: Thanks to a SIGCSE special projects grant, the CS Circles project is now open-source! This means that you can write and remix lessons and exercises to suit your own needs, run your own copy on a local network, or edit the backend. For obtaining and using sources, visit: http://cscircles.cemc.uwaterloo.ca/source/ In other recent news, this summer we added student management, error hints (thanks to A. Okeowo), integrated visualization, and a German translation of the site (thanks to BWINF). If you have any questions, please contact us at cscircles(a)uwaterloo.ca. To unsubscribe from further announcements (about once per year), visit http://cscircles.cemc.uwaterloo.ca/wp-admin/profile.php -- Jurgis Pralgauskis tel: 8-616 77613; Don't worry, be happy and make things better ;) http://galvosukykla.lt

1 0

setting the stage (short essay)
by kirby urner 27 Aug '13

27 Aug '13

At my upcoming workshop in Chicago I'm planning to stress the relevance of theater as *the* extended metaphor where scripting and browsing is concerned. JavaScript pulls the the strings of our DOM, the scenery or structure of the web page stage, while Servers are even further behind the scenes than backstage. They're remote, in the cloud, and help with keeping the AJAX goin', with JSON. The fact that theater is ancient Greek and that we use words like "ajax" and "jason" is no accident. And this is where the mythical roots around Python come in, the familiar serpent and/or dragon atop a treasure trove, the database (say Oracle) in modern verbiage. Hobbits know this archtype, but then so did the ancient Greeks. Apollo actually attacks the Python in one chapter, chasing it away from Delphi, presumably to impose his dreary patriarchy in opposition to Athena's and her priestesses'. One would expect some Athena fan club to claim said Python as a mascot and even say it never died (such things are eternal dontcha know). I have evidence of such a cult. I should explain that the Python is believed to have lived in a cave under the temple at Delphi, the place you go for advice from the priestesses. Here's a scholarly passage: http://bit.ly/17i3akK (goes to Google books, probably *too* scholarly but what I could find at the moment, confirms the gist of the tale above). Anyway, that's to sort of set the stage. A more foreground story would be my reintroduction to lobbying in Oregon, when what was then called the Software Association of Oregon put some muscle behind testing the legislature regarding adding more of this "computer stuff" to the high school curriculum in a way that would help satisfy the math requirement.** A lot of kids were dreading Algebra II, having hated Algebra I and Geometry. You wouldn't need to be a genius to switch gears and start playing with the bash shell, accessing Python, a back door into LAMP. Something like I was already doing with Saturday Academy, with Hillsboro Police Dept. (West Precinct) a client. But I don't think it was the legislature per se that set up any roadblocks. It's just there's not much leverage in that world of mass textbook publishing. Vast funds have already been committed. Tilting at windmills. Live and learn. Make do with what you've got. Speaking of Algebra II, there's that article in this issue of Harper's about where we might be going with that. I had my own review in the Math Forum per usual (an old haunt of mine): http://mathforum.org/kb/thread.jspa?threadID=2591789 (as usual, I'm opinionated in this opinion column) The theme of the workshop is Leveraging Python and I think that dovetails nicely with Guido's CP4E and where are we now lo these many years later? To some extent the answers hinge on several ongoing debates about the shape of education. Some people maintain that programming traces back to humanities topics, such as scripting and play writing. If programming is to become more pervasive is this because of changes in math class or in language arts? A combination? Do we too easily give in to the idea of computing as "number crunching" whereas so often it's "pattern finding" -- more lexical and/or graphical than strictly numeric? Rhetorical question. Here's a recent sketch of the "theater" model for use in the classroom. Of course more gifted drawers than I will freely improve upon my humble rendering. http://www.flickr.com/photos/kirbyurner/9583829639/ Kirby ** An earlier exposure to Oregon lobbying was through my job as a client-server programmer working in FoxPro. Associated Oregon Industries (AOI) was my client and for awhile I was accustomed to seeing Salem more from that point of view. FoxPro's days were numbered though, and my career took me onward.

1 1

LON-CAPA style problems
by Paul-Olivier Dehaye 22 Aug '13

22 Aug '13

Hello, I m looking for LON CAPA style quizz problems to help learn python. Ideally each of these would be focused on individual parts of the python grammar or a subtlety of python. These quizz problems would be used in addition to more classical homework. Does anybody know if any of those LON CAPA problems are publicly available? Thank you Paul-Olivier Dehaye

2 1

Tetrahedron class with volume computer based on edges only
by kirby urner 17 Aug '13

17 Aug '13

""" Euler volume, modified by Gerald de Jong http://www.grunch.net/synergetics/quadvols.html Kirby Urner (c) MIT License """ from math import sqrt, hypot class Tetrahedron: """ Takes six edges of tetrahedron with faces (a,b,d)(b,c,e)(c,a,f)(d,e,f) -- returns volume if ivm and xyz """ def __init__(self, a,b,c,d,e,f): self.a, self.a2 = a, a**2 self.b, self.b2 = b, b**2 self.c, self.c2 = c, c**2 self.d, self.d2 = d, d**2 self.e, self.e2 = e, e**2 self.f, self.f2 = f, f**2 def ivm_volume(self): ivmvol = ((self._addopen()- self._addclosed() - self._addopposite())/2) ** 0.5 return round(ivmvol,5) def xyz_volume(self): ivmvol = sqrt(8/9) * self.ivm_volume() return round(ivmvol,5) def _addopen(self): a2,b2,c2,d2,e2,f2 = self.a2, self.b2, self.c2, self.d2, self.e2, self.f2 sumval = f2*a2*b2 sumval += d2 * a2 * c2 sumval += a2 * b2 * e2 sumval += c2 * b2 * d2 sumval += e2 * c2 * a2 sumval += f2 * c2 * b2 sumval += e2 * d2 * a2 sumval += b2 * d2 * f2 sumval += b2 * e2 * f2 sumval += d2 * e2 * c2 sumval += a2 * f2 * e2 sumval += d2 * f2 * c2 return sumval def _addclosed(self): a2,b2,c2,d2,e2,f2 = self.a2, self.b2, self.c2, self.d2, self.e2, self.f2 sumval = a2 * b2 * d2 sumval += d2 * e2 * f2 sumval += b2 * c2 * e2 sumval += a2 * c2 * f2 return sumval def _addopposite(self): a2,b2,c2,d2,e2,f2 = self.a2, self.b2, self.c2, self.d2, self.e2, self.f2 sumval = a2 * e2 * (a2 + e2) sumval += b2 * f2 * (b2 + f2) sumval += c2 * d2 * (c2 + d2) return sumval PHI = sqrt(5)/2 + 0.5 R =0.5 D =1.0 import unittest class Test_Tetrahedron(unittest.TestCase): def test_unit_volume(self): tet = Tetrahedron(D, D, D, D, D, D) self.assertAlmostEqual(tet.ivm_volume(), 1.0, "Volume not 1") def test_unit_volume(self): tet = Tetrahedron(R, R, R, R, R, R) self.assertAlmostEqual(tet.xyz_volume(), 0.11785, "Volume not 1") def test_phi_edge_tetra(self): tet = Tetrahedron(D, D, D, D, D, PHI) self.assertAlmostEqual(tet.ivm_volume(), 0.70711) def test_right_tetra(self): e = hypot(sqrt(3)/2, sqrt(3)/2) # right tetrahedron tet = Tetrahedron(D, D, D, D, D, e) self.assertAlmostEqual(tet.xyz_volume(), 1.0, "Volume not 1") if __name__ == "__main__": unittest.main()

1 0