Mailman 3 December 2015 - Edu-sig

a short essay about programming
by kirby urner Dec. 8, 2022

Dec. 8, 2022

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 July 2, 2018

July 2, 2018

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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genetic_code.py (another rich data structure)
by kirby urner Dec. 17, 2015

Dec. 17, 2015

# -*- coding: utf-8 -*- """ Created on Wed Dec 16 10:07:57 2015 @author: kurner, 4dsolutions (.net) (copyleft MIT license, 2015) Example: Rich Data Structures (for learning Python, including sqlite3) Source: http://www.soc-bdr.org/rds/authors/unit_tables_conversions_and_genetic_dict… Any errors you discover in transcribing will be mine, please let me know and I'll correct my copy as well. kirby.urner(a)gmail.com Re: "Rich Data Structures" https://mail.python.org/pipermail/edu-sig/2006-June/006608.html (a more obvious need now that "big data" examples are in demand, for learning map/reduce techniques etc.). Indeed, we have many public raw data sets. A goal is to have some already in Python, as ready-to-go native data types. As here. This is not "big data", just data. Another experiment: https://mail.python.org/pipermail/edu-sig/2012-December/010709.html (same caveats about errors) """ amino_acid_abbrevs = \ dict( Phe = 'Phenyalinine', Leu = 'Leucine', Ser = 'Serine', Tyr = 'Tyrosine', Cys = 'Cysteine', Trp = 'Tryptophan', Pro = 'Proline', His = 'Histidine', Gln = 'Glutamine', Arg = 'Arginine', Ile = 'Isoleucine', Met = 'Methionine', Thr = 'Threonine', Asn = 'Asparagine', Lys = 'Lysine', Val = 'Valine', Ala = 'Alanine', Asp = 'Aspartate', Glu = 'Glutamate', Cly = 'Glycine') combos = [(a, b, c) for a in ('G','U','A','C') for b in ('G','U','A','C') for c in ('G','U','A','C')] # Also see: # https://flic.kr/p/BeVwN2 # (American Scientist Vol. 97) mRNA = \ { ('G', 'G', 'G') : 'Gly', ('G', 'G', 'U') : 'Gly', ('G', 'G', 'A') : 'Gly', ('G', 'G', 'C') : 'Gly', ('G', 'U', 'G') : 'Val', ('G', 'U', 'U') : 'Val', ('G', 'U', 'A') : 'Val', ('G', 'U', 'C') : 'Val', ('G', 'A', 'G') : 'Glu', ('G', 'A', 'U') : 'Asp', ('G', 'A', 'A') : 'Glu', ('G', 'A', 'C') : 'Asp', ('G', 'C', 'G') : 'Ala', ('G', 'C', 'U') : 'Ala', ('G', 'C', 'A') : 'Ala', ('G', 'C', 'C') : 'Ala', ('U', 'G', 'G') : 'Trp', ('U', 'G', 'U') : 'Cys', ('U', 'G', 'A') : 'STOP', ('U', 'G', 'C') : 'Cys', ('U', 'U', 'G') : 'Leu', ('U', 'U', 'U') : 'Phe', ('U', 'U', 'A') : 'Leu', ('U', 'U', 'C') : 'Phe', ('U', 'A', 'G') : 'STOP', ('U', 'A', 'U') : 'Tyr', ('U', 'A', 'A') : 'STOP', ('U', 'A', 'C') : 'Tyr', ('U', 'C', 'G') : 'Ser', ('U', 'C', 'U') : 'Ser', ('U', 'C', 'A') : 'Ser', ('U', 'C', 'C') : 'Ser', ('A', 'G', 'G') : 'Arg', ('A', 'G', 'U') : 'Ser', ('A', 'G', 'A') : 'Arg', ('A', 'G', 'C') : 'Ser', ('A', 'U', 'G') : 'Met', ('A', 'U', 'U') : 'Ile', ('A', 'U', 'A') : 'Ile', ('A', 'U', 'C') : 'Ile', ('A', 'A', 'G') : 'Lys', ('A', 'A', 'U') : 'Asn', ('A', 'A', 'A') : 'Lys', ('A', 'A', 'C') : 'Asn', ('A', 'C', 'G') : 'Thr', ('A', 'C', 'U') : 'Thr', ('A', 'C', 'A') : 'Thr', ('A', 'C', 'C') : 'Thr', ('C', 'G', 'G') : 'Arg', ('C', 'G', 'U') : 'Arg', ('C', 'G', 'A') : 'Arg', ('C', 'G', 'C') : 'Arg', ('C', 'U', 'G') : 'Leu', ('C', 'U', 'U') : 'Leu', ('C', 'U', 'A') : 'Leu', ('C', 'U', 'C') : 'Leu', ('C', 'A', 'G') : 'Gln', ('C', 'A', 'U') : 'His', ('C', 'A', 'A') : 'Gln', ('C', 'A', 'C') : 'His', ('C', 'C', 'G') : 'Pro', ('C', 'C', 'U') : 'Pro', ('C', 'C', 'A') : 'Pro', ('C', 'C', 'C') : 'Pro'} # [Ibid, www.soc-bdr.org] from Table 5. Genetic Code: # mRNA condon -> tRNA anti-codon # DNA column dropped (computable, replace mRNA U with T) # last column also not included. tRNA = \ { ('U','U','U'):(('A','A','A'), ('A','A','G')), ('U','U','C'):(('A','A','G'),), ('U','U','A'):(('A','A','U'),), ('U','U','G'):(('A','A','U'),('A','A','C')), ('U','C','U'):(('A','G','I'),('A','G','G'), ('A','G','A')), ('U','C','C'):(('A','G','I'),('A','G','G')), ('U','C','A'):(('A','G','I'),('A','G','U')), ('U','C','G'):(('A','G','C'),('A','G','U')), ('U','A','U'):(('A','U','A'),('A','U','G'),), ('U','A','C'):(('A','U','G'),), ('U','A','A'):(('A','U','U'),), ('U','A','G'):(('A','U','C'),('A','U','U')), ('U','G','U'):(('A','C','A'),('A','C','G')), ('U','G','C'):(('A','C','G'),), ('U','G','A'):(('A','C','U'),), ('U','G','G'):(('A','C','C'),), ('C','U','U'):(('G','A','I'),('G','A','G'),('G','A','A')), ('C','U','C'):(('G','A','I'),('G','A','G')), ('C','U','A'):(('G','A','I'),('G','A','U')), ('C','U','G'):(('G','A','C'),('G','A','U')), ('C','C','U'):(('G','G','I'),('G','G','G'),('G','G','A')), ('C','C','C'):(('G','G','I'),('G','G','G')), ('C','C','A'):(('G','G','I'),('G','G','U')), ('C','C','G'):(('G','G','C'),('G','G','U')), ('C','A','U'):(('G','U','A'),('G','U','G')), ('C','A','C'):(('G','U','G'),), ('C','A','A'):(('G','U','U'),), ('C','A','G'):(('G','U','C'),('G','U','U')), ('C','G','U'):(('G','C','I'),('G','C','G'),('G','C','A')), ('C','G','C'):(('G','C','I'),('G','C','G')), ('C','G','A'):(('G','C','I'),('G','C','U')), ('C','G','G'):(('G','C','C'),('G','C','U')), ('A','U','U'):(('U','A','I'),('U','A','G'),('U','A','A')), ('A','U','C'):(('U','A','I'),('U','A','G')), ('A','U','A'):(('U','A','I'),('U','A','U')), ('A','U','G'):(('U','A','C'),), ('A','C','U'):(('U','G','I'),('U','G','G'),('U','G','A')), ('A','C','C'):(('U','G','I'),('U','G','G')), ('A','C','A'):(('U','G','I'),('U','G','U')), ('A','C','G'):(('U','G','C'),('U','G','U')), ('A','A','U'):(('U','U','A'),('U','U','G')), ('A','A','C'):(('U','U','G'),), ('A','A','A'):(('U','U','U'),), ('A','A','G'):(('U','U','C'),('U','U','U')), ('A','G','U'):(('U','C','A'),('U','C','G')), ('A','G','C'):(('U','C','G'),), ('A','G','A'):(('U','C','U'),), ('A','G','G'):(('U','C','C'),('U','C','U')), ('G','U','U'):(('C','A','I'),('C','A','G'),('C','A','A')), ('G','U','C'):(('C','A','I'),('C','A','G')), ('G','U','A'):(('C','A','I'),('C','A','U')), ('G','U','G'):(('C','A','C'),('C','A','U')), ('G','C','U'):(('C','G','I'),('C','G','G'),('C','G','A')), ('G','C','C'):(('C','G','I'),('C','G','G')), ('G','C','A'):(('C','G','I'),('C','G','U')), ('G','C','G'):(('C','G','C'),('C','G','U')), ('G','A','U'):(('C','U','G'),('C','U','A')), ('G','A','C'):(('C','U','G'),), ('G','A','A'):(('C','U','U'),), ('G','A','G'):(('C','U','U'),('C','U','C')), ('G','G','U'):(('C','C','I'),('C','C','G'),('C','C','A')), ('G','G','C'):(('C','C','I'),('C','C','G')), ('G','G','A'):(('C','C','I'),('C','C','U')), ('G','G','G'):(('C','C','C'),('C','C','U')) }

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Python Education Summit 2016
by Chalmer Lowe Dec. 10, 2015

Dec. 10, 2015

Team: The Python Education Summit is on again this year at the PyCon in Portland. A couple of things are the same, a couple of things are gonna change... 0) *Keeping the conversation going*: last year, we talked about ways to keep the conversation going through out the year and many of the ideas we suggested never took off. Please join us on the new *PythonEDU Slack Team* (see below) so we can revisit those ideas and see what we can do to increase and improve how we share data and ideas on education and Python. 1) *Slack Team: PythonEDU* - All work by the Planning Committee for the Summit as well as general conversations about the Summit are gonna run through a Slack Team (if you want an invite, let me know... *I have to manually invite folks - weakness of slack, not my preference*). 2) *Volunteer*: we need participants on the Planning Committee >>> if you want to be included in the conversation, let me know so I can add you to the Slack Team. 3) *Call for Papers:* Talk submissions go through the same talk submission process as any other PyCon talk. While I loved the idea of using moderator, as we looked at the logisitics, there were too many weaknesses in that process to continue. You only have til January 3rd to submit talks. Get in there and do it! https://goo.gl/iCKOWY 4) *What to include in the Summit*: We are brainstorming ideas for what to include in the edusummit. The ideas will be hashed out by the Planning Committee. Let us know what you want to see! 5) *Twitter*: our twitter hashtag will be #pythonedu 6) *Registration for the Summit:* There are some glitches that need to be worked out in regards to getting folks registered to participate in the Summit. I am looking into that. More to come. Respectfully, Chalmer Lowe Chairman of the Python Education Summit -- Chalmer Lowe, MS PyHawaii Dark Art of Coding Booz Allen Hamilton

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more from my classroom
by kirby urner Dec. 10, 2015

Dec. 10, 2015

Here's some more code from the night class I'm teaching, invisibly in the sense it's all virtual, but in real time, different from my usual asynchronous gig based on evaluating student work. About twenty login and we have our private session, company tech support listening in for Q/A. Complementary synchronous work, with students off the hook but welcome and often eager to dive in (I don't see their desktops usually, though they're free to share). The code below started out as a Lab where I just suggested using trial by division (I described the approach) in the context of an iterator. We're just at that point where "iterator" (versus iterable) is coming together with these new grammatical constructs, these new underscore names. We're also tackling decorators and context managers around this same time. # -*- coding: utf-8 -*- """ Created on Tue Dec 8 17:39:27 2015 @author: Kirby Urner, 4Dsolutions.net (copyleft) MIT License, 2015 Two models of iterator that do the same thing. All primes found so far will be a list of all primes <= n without any missing. Algorithm: trial by division. """ def next_prime(): """ creates an iterator that spits out successive prime numbers """ so_far = [2] yield 2 n = 2 while True: n += 1 for divisor in so_far: if divmod(n, divisor)[1] == 0: # goes evenly break if divisor ** 2 > n: yield n so_far.append(n) break class Primes: """ creates an iterator that spits out successive prime numbers """ def __init__(self): self.so_far = [2] self.n = 2 def __iter__(self): return self def __next__(self): if self.n == 2: self.n += 1 return 2 while True: for divisor in self.so_far: if divmod(self.n, divisor)[1] == 0: # goes evenly break if divisor ** 2 > self.n: self.so_far.append(self.n) self.n += 1 return self.so_far[-1] self.n += 1 There's a license on it not because I think I'm being all that original i.e. these is not genius math or anything. I've been told people are more comfortable sharing if there's at least some explicit attention to sharing rights. The point for purposes of my class was to show two ways to write an iterator, using function generator syntax or a class with the __next__, __iter__ protocol. The latter is a refactoring of the former, or vice versa. However, putting on my "used to be a high school math teacher" hat, I really like this naive ramping up into Primeville. As an algorithm it sputters if your goal is working with uber-primes ala RSA or whatever, but this is not about dissing algorithms its about learning what "algorithm" means. Also the difference between prime and composite. I found myself bringing up the Fundamental Theorem of Arithmetic again, just like the old days (I haven't been a full time high school math teach since the early 1980s, spent a lot more years coding in FoxPro :-D). >>> g = next_prime() >>> [next(g) for _ in range(20)] [2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71] >>> g = Primes() >>> [next(g) for _ in range(20)] [2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71] Other news from my angle... We're enjoying lots of action on python-cuba (a workgroup) -- some planning conference coming up on the 12th. Public archive, check it out. https://mail.python.org/mailman/listinfo/python-cuba Also I'm sometimes chiming in on the Chipy listserv, one of my favorites. Portland's is quiet by contrast (I'm in Portland -- born in Chicago though). Kirby

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generating phi as continued fraction (inefficient version)
by kirby urner Dec. 5, 2015

Dec. 5, 2015

Inefficient, but still kinda fun. I used it last night as an introduction to eval( ). First I take the eval away and show the expression (growing) being generated (it's a generator). 1 + 1/(1) 1 + 1/(1+ 1/(1)) 1 + 1/(1+ 1/(1+ 1/(1))) 1 + 1/(1+ 1/(1+ 1/(1+ 1/(1)))) 1 + 1/(1+ 1/(1+ 1/(1+ 1/(1+ 1/(1))))) 1 + 1/(1+ 1/(1+ 1/(1+ 1/(1+ 1/(1+ 1/(1)))))) 1 + 1/(1+ 1/(1+ 1/(1+ 1/(1+ 1/(1+ 1/(1+ 1/(1))))))) 1 + 1/(1+ 1/(1+ 1/(1+ 1/(1+ 1/(1+ 1/(1+ 1/(1+ 1/(1)))))))) and so on. Then I switch to eval-ing the expression and, lo and behold, we're approaching phi aren't we. 2.0 1.5 1.6666666666666665 1.6 1.625 1.6153846153846154 1.619047619047619 1.6176470588235294 1.6181818181818182 1.6179775280898876 1.6180555555555556 1.6180257510729614 1.6180371352785146 1.6180327868852458 1.618034447821682 1.618033813400125 1.6180340557275543 1.6180339631667064 1.6180339985218035 1.618033985017358 Way back in the annals of edu-sig, early years, we were digging into HOW-TO re continued fractions and exploring the more optimized algorithms. Sometimes though, it's just the concepts you need -- optimization in another sense. eval( ) and exhibiting a sequence of generators was the theme. I used the pi-digits generator we talked about this September (here on edu-sig), and that one of Ramanujan's, the latter posted here yesterday in Python 3.5 version. Kirby # -*- coding: utf-8 -*- """ Created on Thu Dec 3 16:08:49 2015 @author: kurner Another generator example: converging to Phi Shows eval( ) in action """ def continued(): patt = "+ 1/(1" the_expr = '' # empty n = 1 while True: the_expr = the_expr + patt the_frac = "1 " + the_expr + ")" * n yield eval(the_frac) # or show the_frac n += 1 the_gen = continued() for _ in range(20): print(next(the_gen))

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introducing euler's number
by kirby urner Dec. 4, 2015

Dec. 4, 2015

Again from tonight's class prep. Such scripts might be useful exhibits if you're still trying to get approval to move beyond a TI calculator in math class. Playing with extended precision helps bring the concepts of limits and convergence alive. My students are employed adults so winning such approval is a non-issue. But then I ask them to imagine themselves back in school, with Python a tool of choice in math class. Wouldn't that have been great!? Kirby # -*- coding: utf-8 -*- """ Created on Thu Dec 3 16:40:46 2015 See: http://www.miniwebtool.com/first-n-digits-of-e/?number=300 @author: kurner LAB: Write a unittest to confirm convergence to e to 300 places. after n steps. """ import unittest from decimal import * def euler(n): n = Decimal(n) one = Decimal(1) return (one + one/n) ** n class Test_e(unittest.TestCase): def test_outcome(self): expected = ('2.718281828459045235360287471352662' '49775724709369995957496696762772407' '66303535475945713821785251664274274' '66391932003059921817413596629043572' '90033429526059563073813232862794349' '07632338298807531952510190115738341' '87930702154089149934884167509244761' '46066808226480016847741185374234544' '2437107539077744992069') with localcontext() as c: c.prec = 400 result = euler('1' + '0' * 301) self.assertEqual(str(result)[:len(expected)], expected) if __name__ == "__main__": unittest.main()

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time passing: ramanujan and pi
by kirby urner Dec. 4, 2015

Dec. 4, 2015

Looking back: https://mail.python.org/pipermail/edu-sig/2006-September/006963.html shows me still importing __division__ and relying on some factorial off state. Tonight, preparing for class, I'm able to rely on math.factorial, introduce other improvements. # -*- coding: utf-8 -*- """ Created on Thu Dec 3 16:40:46 2015 See: https://crypto.stanford.edu/pbc/notes/pi/ramanujan.html @author: kurner LAB: Write a unittest to confirm convergence to: '3.141592653589793238462643383279502884197169 39937510582097494459230781640628620899862803 48253421170' after n steps (this is the answer key version) """ import unittest from decimal import * from math import factorial as fact def pieinsky(): c1 = Decimal(4) c2 = Decimal(1103) c3 = Decimal(26390) c4 = Decimal(396) c5 = Decimal(9801) # code formatted for readability (make it be one line) root8 = Decimal('2.82842712474619009760337744841939615' '7139343750753896146353359475981464956' '9242140777007750686552831454700276') i = Decimal(0) thesum = Decimal(0) while True: term = (fact(c1*i)*(c2 + c3*i))/(pow(fact(i),4)*pow(c4,4*i)) thesum = thesum + term yield 1/((root8/c5)*thesum) i += 1 class TestPi(unittest.TestCase): def test_outcome(self): expected = ('3.141592653589793238462643383' '2795028841971693993751058209749445923078' '164062862089986280348253421170') with localcontext() as c: c.prec = 100 the_gen = pieinsky() for _ in range(20): next(the_gen) self.assertEqual(str(next(the_gen))[:len(expected)], expected) if __name__ == "__main__": unittest.main()

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relevant blog posting re pre-college CS topics & Python
by kirby urner Dec. 3, 2015

Dec. 3, 2015

http://controlroom.blogspot.com/2015/12/mathy-memes.html Kirby

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