Mailman 3 July 2016 - 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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Online course & programming competitions for high school students
by Georgina Wilcox 30 Jul '16

30 Jul '16

This year is the 11th year of the NCSS Challenge -- an online programming competition for high school students, run by the University of Sydney, Australia. The competition runs for five weeks, and each week a set of problems and a set of notes are released. Students can use the online marking system to get immediate feedback on their work. There are four difficulty levels, ranging from absolute beginners (suitable for younger students), through to advanced. If you're a teacher and considering using this with your students they have free teacher trials: http://groklearning.com/teachers The competition itself starts on Monday 1st August. I've worked on this challenge as a volunteer for several years, I'd be happy to answer any questions you might have. Otherwise, check out the website: https://groklearning.com/challenge Georgina

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more pythonic andragogy...
by kirby urner 29 Jul '16

29 Jul '16

What I like about the appended module is it exercises constructs in a somewhat meaningless fashion that nevertheless has a story, a strong metaphor. We're in a spooky castle and want to leave having guessed a Python keyword, hidden in self.__xyjk during initialization. If we guess it right in five tries, an exception is raised, but one signalling we're victorious, and so the __exit__ method handles it in a congratulatory manner and returns True, and we're released from the castle without fuss or bother. If we can't guess it in five tries, even after two hints, then the exception is a kick in the pants; we're booted out with an unhandled exception (return False). The outer handler takes care of KickFromCastle in that case. The print() statements tell the story. All pretty pointless... except to those learning Python. Tonight I interleaved the code below with a more serious-looking use of context managers in a Jupyter Notebook. http://bit.ly/2aiFaIA <--- looks through nbviewer (Jupyter Notebook viewer) at one of my Github JNs (just another web page) Kirby == from keyword import kwlist from random import choice import sys class EscapeVictorious(Exception): pass class KickFromCastle(Exception): pass class Castle: def __init__(self, secret): self.__xyjk = secret self.guesses = 0 self.hints = 0 def __enter__(self): """get the ball rolling""" print("Welcome to Spooky Castle. To Escape, " "guess the secret keyword") return self # <-- make me available within scope via 'as' def hint(self): if self.hints == 0: print("The keyword begins with", self.__xyjk[0]) elif self.hints == 1: print("The keyword is", len(self.__xyjk), "letters long.") else: print("You've had your two hints, sorry") self.hints += 1 def query(self): """gradations""" print("So what is the secret keyword then? " " Guess so far:", self.guesses) ans = input("You may answer (or type 'hint'): ") if ans == self.__xyjk: print("Excellent, we're done here") print("You have won the Copper Key") # <-- RealPlayer One (novel) raise EscapeVictorious("Copper Key") elif self.guesses == 5: print("Uh oh, you're out of guesses, sigh") raise KickFromCastle("We're done!") elif ans == "hint": self.hint() return else: self.guesses += 1 print("No, that's not it.") def __exit__(self, *exception_data): """raise a ruckus""" if exception_data[0] == EscapeVictorious: print("Congratulations!") print("Here is your", exception_data[1]) return True if exception_data[0] == KickFromCastle: print("Better Luck Next Time") print("The keyword was", self.__xyjk) return False if __name__ == "__main__": the_secret = choice(kwlist) try: with Castle(the_secret) as spooky: while True: spooky.query() except: print("Handling: ", sys.exc_info()[0].__name__) print(sys.exc_info()[1]) # <--- triggers __str__ print(type(sys.exc_info()[1]))

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teaching Python 3.5 in 2016: snapshot
by kirby urner 28 Jul '16

28 Jul '16

I'm prepping for class tomorrow, as a Python instructor for employed adults eligible for California State funded professional development electives, not for college credit but career-relevant nonetheless. My approach is to use collections.namedtuple to show the tuple (a sequence type, like a list) having its "slots" accessed via dot notation, not just through indexing, then swapping in an equivalent class that does the same thing (down to having __getitem__ in some examples). Seeing how a class duplicates features we've already introduced, makes a nice bridge to "defining your own types" (vs using the __builtins__ or standard library types). Once with have dicts and lists introduced, near the start, we're ready to talk about JSON already, which brings in early previews of web services, APIs, inter-operability with JavaScript (ES) and of course MongoDB. I just use json module to store .json files, as soon as we get to the function open( ), i.e. here's a first example of Talking about Python in the context of getting between a browser and a database or persistent storage, gets the juices flowing about "an ecosystem". These two source code files show off the web API angle, using an open API to get IMDB information (movie database): https://github.com/4dsolutions/Python5/blob/master/get_movie.py https://github.com/4dsolutions/Python5/blob/master/get_movie_v2.py Here's another example, going from namedtuple Element (for Periodic Table atoms), to class-based Element: namedtuple: https://github.com/4dsolutions/Python5/blob/master/elements_02.py class based: https://github.com/4dsolutions/Python5/blob/master/elements_04.py Actually running these would require the *.json files, both included in the repo: elements_v1.json elements_v2.json Next stop: SQLite and try / except syntax. Kirby PS: I'm pushing Pyret pretty seriously even though it's very much the moving target. Follow the action on Twitter @4DsolutionsPDX python-cuba working group also going well. Py2017 shaping up.

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Curriculum Outline (was: no subject)
by kirby urner 27 Jul '16

27 Jul '16

Sorry about the missing subject line. Also I forgot try / except -- this outline was incomplete: For semantics I go: > * basic primitives, including datatypes, dir() help() type() > * functions along with ** and * > * control structures (for/else, while/else, if/elif/else, try/except/finally/else) > * collections.namedtuple --> explicit class-based version > * classes, inheritance > * instance, class, static methods (sans decorator) > * generators, decorators, context managers, descriptors > * some other stuff I'm sure I'm forgetting :-D Here's my class outline for Session 06 to give a better idea of the pacing (we meet twice a week, small class size). We didn't get to Lab 3 which is why 07 started with it. Usually I have three 20 minute labs and up to three 5 minute breaks per 4 hour session. We have live scrolling chat window. I generally keep cameras off except the one on me, so they have a small postage stamp talking head and then the coding surface as center stage. I can highlight and circle with graphics widgets but mostly just use the mouse to make chunks or lines turn color. See also: https://mail.python.org/pipermail/edu-sig/2016-July/011503.html # -*- coding: utf-8 -*- """ Created on Thur Jul 21, 2016 Course: PYT-PR (Saisoft.net) Session 06 Instructor: Kirby Urner kirby.urner(a)gmail.com @thekirbster Audio Check (6:15 PM PDT) Introduction: API: control surface, interface Web API: web services (REST vs SOAP) Python types: API may use special names __ribs__ __ribs__: __getitem__, __init__, __repr__, __call__, __dict__ Side-by-side: namedtuple versus class (same API) A menu-driven application (Periodic Table): modules importing modules input validation techniques LAB 1: user selects which column to order by when printing (Requires a submenu of column choices) classes (same as types): inheritance instance methods versus class methods versus static methods LAB 2: keep track of heros and monsters using class-level dict Example API: datetime.timedelta Example API: File Type Objects (returned by open()) Types: filetype, enumerate, sys sys.argv Writing a command line utility LAB 3: print any Python .py (source code) file with line numbers Summary of Session 06 """

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interesting Jupyter Notebooks useful for teaching Python (on Github)
by kirby urner 27 Jul '16

27 Jul '16

http://nbviewer.jupyter.org/github/4dsolutions/Python5/blob/master/Atoms%20… (Atom class ideas) http://nbviewer.jupyter.org/github/4dsolutions/Python5/blob/master/Pi%20Day… (tau stuff) http://nbviewer.jupyter.org/github/4dsolutions/Python5/blob/master/Polyhedr… (linear algebra) http://nbviewer.jupyter.org/github/4dsolutions/tetravolumes/blob/master/Com… (philosophy for physics majors) http://nbviewer.jupyter.org/github/4dsolutions/Python5/blob/master/STEM%20M… (sphere packing stuff) Take off the nbview viewer prefix and use just use the github part to access the raw materials. Kirby

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(no subject)
by kirby urner 27 Jul '16

27 Jul '16

Here was my Lesson 07 of 10 for Saisoft.net (July 2016). I've been doing a series of Python courses for them, as shown in earlier postings to this archive. In a followup post, I'll list some of the Jupyter Notebooks we toured, plus the one I've developed for MathFuture (a Google Goup). I'm finding this a fruitful approach: * start with Anaconda distro * use Spyder for IDE but also demonstrate "bare command line + vim" type dev styles * take Python fluency developed in Spyder and copy-paste-adapt to Jupyter Notebooks * go back to IDE, but keep using JN. I show the Raspberry Pi as a physical device on camera and suggest getting one, case might be 3D printed. We don't actually try making the Pi join us on zoom.us (our multimedia teaching platform), but that's an experiment I might try. I refer to the REPL as my "chalk board", "scratch sheet", "doodle pad","chat window" (chatting with Python) as well as my "repl" The editor window is more self explanatory. Spyder gives us the green Run Arrow to merge "__main__" with the doodle pad's namespace. Useful to write scripts, run, then doodle with the created functions and classes. For semantics I go: * basic primitives, including datatypes, dir() help() type() * functions along with ** and * * collections.namedtuple --> explicit class-based version * classes, inheritance * instance, class, static methods (sans decorator) * generators, decorators, context managers, descriptors But always with spiraling i.e. we keep going back to the beginning and iterating through a bunch of stuff. Kirby # -*- coding: utf-8 -*- """ Created on Tue Jul 26, 2016 Course: PYT-PR (Saisoft.net) Session 07 Kirby Urner Instructor: kirby.urner(a)gmail.com @thekirbster Audio Check (6:15 PM PDT) Introduction: Python's Pillar Communities (three of many) web developers API (Django, Web2py, Flask, Pyramid...) STEM professionals (Anaconda / scipy / Enthought...) Animation / Graphics (pillow, Blender, vpython, pi3d) Continuing from last week: Example API: File Type Objects (returned by open()) Types: filetype, enumerate, sys, sys.argv Writing a command line utility LAB 1: write utility to print python source to console w/ line numbers Shifting gears... Jupyter Notebooks (come for free with Anaconda distro) ($ pip install will get you there too) Periodic Table in Jupyter Notebook http://nbviewer.jupyter.org/... github/4dsolutions/Python5/blob/master/Atoms%20in%20Python.ipynb LAB 2: get 'Atoms R Us' NB running on your localhost unittest and the importance of unit testing (PyUnit from JUnit) pytest, nose.... 3rd party offerings are great too! LAB 3: add more unittesting methods to Atoms R Us and/or adapt the Movie Database API code to Jupyter context Tour of more Jupyter Notebooks with hints of upcoming topics (decorator @) (generator yield) (with) Summary of Session 07 """

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Presentation on Learning Math with Python
by Peter Farrell 26 Jul '16

26 Jul '16

Hello! The Bay Area Python Interest Group invited me to speak at LinkedIn last Thursday about using Python in math education. They asked that I work in something about the Raspberry Pi, which (as the organizer of the SF Peninsula Raspberry Pi Meetup group) I took as an invitation to overdo it. So I loaded all my programs on my Pi 3 and did the whole presentation on it: the slides, my Python programs, a web search and my Minecraft maze and big honkin' pyramid. People liked the visual, interactive, 3D stuff I showed them but they seemed particularly blown away that I did the whole presentation on a Pi. They made me hold it up afterwards to prove it. [image: Inline image 1] Yes, that's the 2D cellular automaton from page 172 of Wolfram's New Kind of Science, in Minecraft. LinkedIn was recording it but they said it'll be a while before they post it. My colleague Ken Hawthorne was filming, too, and has posted his video here <https://vimeo.com/175855273>. Long story short, showing off is fun but I'd love to work with math teachers and help them incorporate Python programming into all their math lessons. And when they get some experience under their belt they'll be able to do more challenging explorations like fractals, cellular automata and 3D graphics. I never said it's going to be easy, but it can be more rewarding and meaningful than the way I learned math back in the day. Let me know what you think! Peter

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