Mailman 3 December 2013 - 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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Re: [Edu-sig] RurPLE-NG is nice
by Jurgis Pralgauskis April 5, 2014

April 5, 2014

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 :)

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Easy Web Environment to post pupils Python Creations
by Philip Bagge April 1, 2014

April 1, 2014

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

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Annotate Algorithms in Python
by DiPierro, Massimo Dec. 19, 2013

Dec. 19, 2013

Welcome everybody, I just finished a book on Numerical Algorithms in Python: http://www.amazon.com/Annotated-Algorithms-Python-Applications-Physics/dp/0… It covers many algorithms including: - merge sort - binary sort - heap sort - priority queues - tree search - tree traversing - topological sort - Dijkstra - Prim - disjoint sets - Huffman encoding - linear algebra - Cholesky - Gauss-Jordan - sparse matrix inversion (minres, bicgstab) - Newton solver - Newton optimizer - bisection method - secant method - golden section method - multi-dimensional solver - least squares - chi square fitting - numerical integration by quadrature - Fourier transform and fft - random number generators - Monte Carlo simulations - parallelization with mpi4py, pyOpenCL, and OCL - Map-Reduce They all come with examples and applications. The book contains the entire source code (pure python) and does use numpy. The point of the book is not teaching existing API but showing/discussing python code. Most of the code presented in the book can be downloaded here: https://github.com/mdipierro/nlib Massimo

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OSCON 2014: Call for Participation (proposals due Jan 30).
by Kirby Urner Dec. 18, 2013

Dec. 18, 2013

OSCON, the annual Open Source Convention held in Portland OR, will be held next year from July 20-24. The call for participation has now been published, and there will again be a Python track. Please see the full call at http://www.oscon.com/oscon2014/public/cfp/308. Submissions for 3-hour tutorials and 40-minute talks are due by January 30, 2104.

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the Python ecosystem...
by kirby urner Dec. 13, 2013

Dec. 13, 2013

We've been discussing the evolving Raspberry Pi picture on MathFuture somewhat (overlapping contributors), noting Wolfram Language throwing itself in the ring, as another language the Pi supports. My Gchat with Indonesia this evening was about that. I had another Hangout with the eduSummit gang. We experimented with Google Moderator as a means of working with whatever our Call for Proposals manages to generate. Steve Holden set up a "Pi Lab" with four identical workstations, a man named Trevor (suitably UK-sounding) coming in once a week. We didn't get wolfram-engine running yet, but only because we've been lazy, I suppose one might charge (been really busy). http://www.flickr.com/photos/kirbyurner/11319784916/in/photostream/ (picture of Pi Lab, opening day) I've been wanting to spin up an Amazon instance with Vpython already going, which one would think'd be a piece of cake, except when do I find the time? I'd like to demo some Python5 code options maybe, what could we do with these additional libraries? I should yak with Traction Station. VPython on the Pi... a possibility? I just need to Google some more... probably been done. https://groups.google.com/forum/#!topic/vpython-users/8YnuZa6w7m8 So my question for Indonesia was "would school systems switch?" now that a student could have a Pi + Mathematica for less cost than a scientific calculator with far less than half the brains. Imagine some high school class, say Calculus. Of course there's an easy answer to that one: some will / some won't (plus some aren't in the posited initial position so not able to "switch"). Your level of support is far higher in the UK I'd say, at the moment. But then of course Wolfram Language isn't about which side of the Atlantic (or Pacific) you're on. Kirby

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