Mailman 3 November 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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discrete math track (high school) + a sieve
by kirby urner 16 Nov '17

16 Nov '17

We've maybe seen this sieve before on edu-sig but I don't remember for sure, and just came across it following links from Guido's blog. So pithy! # -*- coding: utf-8 -*- """ Created on Thu Nov 16 13:23:51 2017 Copied from: http://www.mypy-lang.org/examples.html """ import itertools def iter_primes(): # An iterator of all numbers between 2 and # +infinity numbers = itertools.count(2) # Generate primes forever while True: # Get the first number from the iterator # (always a prime) prime = next(numbers) yield prime # This code iteratively builds up a chain # of filters... numbers = filter(prime.__rmod__, numbers) for p in iter_primes(): if p > 1000: break print(p) ------- Also, anyone interested in debates regarding the future of high school math might be interested in math-teach, likely to be frozen and/or disappeared come first of next year. Lots of politics (I'm not a listowner nor on staff, have limited insight, see 2nd link below): http://mathforum.org/kb/message.jspa?messageID=10283328 https://www.nctm.org/News-and-Calendar/Messages-from-the-President/Archive/… Kirby

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How to define "a Python project"?
by Aivar Annamaa 08 Nov '17

08 Nov '17

Hi! Python programs which involve a single *.py file are easy to manage -- eg. it's clear what is meant with "opening" or "running" the program. In case of larger programs or in the context of a course (sequence of exercises) it would make sense to somehow group a bunch of Python (and other) files. Matthew Jadud recently brought this up in Microbit list (See "2. Projects vs. Files" in https://mail.python.org/pipermail/microbit/2017-October/001721.html). I'm considering adding the (optional) concept of "project" into my Python IDE (http://thonny.org). In my current vision this would bring: * an extra pane showing the files of the project * actions "Create project..." and "Select project..." * actions "Import project ..." and "Export project..." o Target could be GitHub, EduGit, zip-file, FTP, another folder, ... * Bonus: In case of projects originating from Git there could be also "Sync" action. Can you point out some good examples of Python project management? What could be good format for defining the project? Just a folder? A folder with a configuration file or subfolder? __init__.py? __main__.py? setup.py? .git? Something else? Teachers could prepare and distribute starter projects. What are the things that could go there besides library code and templates? Test cases? Linter configuration? Something else? Any other thoughts regarding Python projects in the educational context? How do your students transfer files between computer lab and their home computers? How do they submit code? Would the concept or "project" simplify this? best regards, Aivar Annamaa

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congrats to SciPyLA (Latin America) on nailing dates
by kirby urner 03 Nov '17

03 Nov '17

Followup: https://mail.python.org/pipermail/python-cuba/2017-November/000290.html I would argue that a contemporary Python workstation, appropriately beefed up with software libre, ala numpy / scipy, has enough embedded graphics capability to hold the fort. https://flic.kr/p/D17NrN (screen shot: Spyder with embedded plots in the REPL) A billboard campaign aimed at getting numpy in high schools, would make a lot of sense. I press my case on Math Forum: http://mathforum.org/kb/message.jspa?messageID=10273676 The curriculum stays weak to the extent we expect "technology in the classroom" to mean calculators. Kirby

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