Mailman 3 September 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

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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 :)

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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

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PyconUK education track
by Nicholas H.Tollervey 03 Oct '13

03 Oct '13

-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 Hi, Here's a write-up (one of many, but it's mine) about the PyconUK 2013 education track for teachers, students and developers that happened last weekend: http://ntoll.org/article/pyconuk2013-roundup It was a great success and a lot of fun was had by all..! Here's to more of the same next year. N. -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.12 (GNU/Linux) Comment: Using GnuPG with Icedove - http://www.enigmail.net/ iQEcBAEBAgAGBQJSRzDYAAoJEP0qBPaYQbb6spIIALHmxdi840zCmYUqs1V4RAwx RbSwdxB9AeZpewgKX4KmquvK1I3/szsF0iRMrV5EPDBd4nPLmPlEGif+RpecMTZH iLnS95fWDYZE9h6uD9jus47662oZz0dUAoMrGsxh5WpuyA41uE+ngLvc/up3S9Id 8kmUaOjBamNIlsFooxIoLhSgqIWVS6DOn+Nv+/IpAQLo7UtSzVxnej3zHozqgMzI DpwYqxbFw0WGts3yrzBJkuQQSYLJj9hjEgh415ir+MUSwLRIMbb965GwEOr1MKBj ATInlgj6dt1GuDOMHqeCVIV706vOyze4U8mBhy7d+APzJnYPJ9T1JB3WhW/Zm3o= =J6pU -----END PGP SIGNATURE-----

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bookdemo.py (a Visual Python animation -- reprogrammable)
by kirby urner 29 Sep '13

29 Sep '13

""" A Visual Python animation showing a "triangular page" going back and forth between triangular book covers laid flat against the XY plane. The page tip traces a semi-circle (not displayed but certainly computed). As a result of two triangular "flaps" (cover and page) at some dihedral angle, a tetrahedron is defined, actually two, one with each cover as base, tip as opposite vertex. Their volumes will always be the same. The video pauses in two places (time.sleep()). The Tetrahedron class (imported) is designed to natively return volume in "tetravolumes" but you can flip that switch easily to use xyz_volume instead. Dependencies: Python 3.x (python.org) Visual Python (vpython.org) stickworks.py (3.x version) https://mail.python.org/pipermail/edu-sig/2013-September/010896.html tetravolumes.py https://mail.python.org/pipermail/edu-sig/2013-August/010872.html (watch for / repair word-wrapping in this code -- too wide for mailman defaults) Videos and more explanation: http://controlroom.blogspot.com/2013/09/polyhedrons-at-play.html """ from tetravolumes import Tetrahedron from stickworks import Vector, Edge import math import time from visual import * # This module runs as "__main__" so the visual stuff kicks it off scene2 = display(title = "Book Covers", width=500, height=500, background=(0,0,0), center=(0,0,0)) scene2.forward = (0,1,-.3) scene2.autocenter = False scene2.range = (2,2,4) scene2.select() # In this namespace, a rod with its tail at the origin is a Vector while some line # segment floating in space with neither end at the origin is an Edge. # So rods like C0--S1 and even the spine and axis themselves are modeled # as Edges, not Vectors. Edges are *defined* using two Vectors however, # one pointing to each end. # S0 --- S1 is the spine, two XYZ Vectors (defined in a different module named # stickworks. I use the Y axis, with Z considered vertical. S0 = Vector((0,0.5,0)) S1 = -S0 spine = Edge(S0, S1) # spine of a book (equilateral triangular book covers) # C0 -- C1 would be the book cover axis from cover to cover, nailed down and # fixed. Again, these are modeled as Vectors. X axis is used. C0 = Vector((math.sqrt(3)/2,0,0)) C1 = -C0 axis = Edge(C0, C1) # another fixed Edge # spine to C0 S0C0 = Edge(S0,C0) S1C0 = Edge(S1,C0) # spine to C1 S0C1 = Edge(S0,C1) S1C1 = Edge(S1,C1) class Page: """ triangular page modeled by its tip oscillating between pages. """ def __init__(self, angle=0): self.angle = angle # degrees self.tip = self._getVector() def delta_angle(self, degrees): self.angle += degrees self.tip = self._getVector() def _getVector(self): #The page tip's job is to make an arc using sine and cosine of the dihedral # angle the page is making with the flap, starting with tip at C0. z = math.sin(math.radians(self.angle)) * axis.length/2 x = math.cos(math.radians(self.angle)) * axis.length/2 y = 0 return Vector((x,y,z)) def complementary(page): a = Edge(page.tip, S0).length b = Edge(page.tip, C0).length c = Edge(page.tip, S1).length d = S0C0.length e = S1C0.length f = spine.length t0 = Tetrahedron(a,b,c,d,e,f) a = Edge(page.tip, S0).length b = Edge(page.tip, C1).length c = Edge(page.tip, S1).length d = S0C1.length e = S1C1.length f = spine.length t1 = Tetrahedron(a,b,c,d,e,f) return t0, t1 def inadvertent(page): # stub function marking a 3rd tetrahedron of opposite # edges green and blue, other edges red, as a fall-out, # like another consequence of the setting for t. Per # Koski's studies. t2 = Tetrahedron( ) return t2 spine.draw() S0C0.draw() S1C0.draw() S0C1.draw() S1C1.draw() lamp = local_light(pos=(0,-3,0), color=color.yellow) page = Page() def drawit(page): s=Edge(page.tip, S0, color=(1,0,0)) t=Edge(page.tip, C1, color=(0,0,1)) u=Edge(page.tip, S1, color=(1,0,0)) v=Edge(page.tip, C0, color=(0,1,0)) s.draw() t.draw() u.draw() v.draw() rate(30) return s,t,u,v def eraseit(*seq): for obj in seq: obj.erase() # a loop drives the page back and forth by upping and lowering # the degrees, of the dihedral angle. So you'll spot where, when I'm # close to "regular tetrahedron" (71 degree) I swap in a dihedral angle # computed with trig -- you could say it's a still snap shot of the ideal, # whereas the animation skips such "irrational" dihedrals. for i in range(4): for t in range(180): page.delta_angle(1) a,b,c,d = drawit(page) if i == 2 and t == 71: page = Page(math.degrees(math.asin( 1/sqrt(3))) * 2) T1, T2 = complementary(page) # choose T1.ivm_volume OR T1.xyz_volume tx =text(text="Vol = {:>6.3f}".format(T1.ivm_volume()), pos=(-1, 0, -1), height=0.4, depth=-0.1, up=(0,0,1), color = color.orange) time.sleep(10) tx.visible = False eraseit(a,b,c,d) # The two stops to display volumes are programmed in. It's not like # I can stop it arbitrarily and have the volume displayed, although the # 2nd video may give that illusion. for t in range(180): page.delta_angle(-1) a,b,c,d = drawit(page) if i == 0 and t == 90: T1, T2 = complementary(page) # choose T1.ivm_volume OR T1.xyz_volume tx =text(text="Vol = {:>6.3f}".format(T1.ivm_volume()), pos=(-1, 0, -1), height=0.4, depth=-0.1, up=(0,0,1), color = color.orange) time.sleep(10) tx.visible = False eraseit(a,b,c,d)

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stickworks.py (Python 3.2 edition)
by kirby urner 29 Sep '13

29 Sep '13

I think the code below is short enough and didactic / general purpose enough to archive / share here on edu-sig, (c) MIT License, versus say Github. It runs with only visual (Visual Python) as a dependency, which makes it a great demo and provides assets out of the box (simple Vector and Edge classes) to use with that excellent package. Then I'm going to post another demo which in turns depends on this module, and on this one: https://mail.python.org/pipermail/edu-sig/2013-August/010872.html This demo will further show how to use stickworks.py (below) as a resource. NOTE: some code may have word-wrapped during transport. Perform standard maintenance before first use. Kirby """ Some infrastructure for working with Vectors and Edges, including an xyplotter generator and axes maker. (c) By Kirby Urner, Sept 13, 2006, 2013, MIT License # no warranty, "as is" (feel free to bring up to your own # standards before using it to build bridges). Originally # for learning purposes. Updated Sept 29, 2006: make Edge color a class-level attribute add funky derivative demo refactor a bit Updated Sept 27, 2013: made Python 3.2 compatible Original Code: http://www.4dsolutions.net/ocn/python/stickworks.py Video: http://youtu.be/4iMSGKXJ_Ds Some relevant discussion: http://mail.python.org/pipermail/edu-sig/2006-September/007145.html http://mail.python.org/pipermail/edu-sig/2006-September/007149.html http://mail.python.org/pipermail/edu-sig/2006-September/007150.html http://mail.python.org/pipermail/edu-sig/2006-September/007312.html """ from visual import vector, cylinder, cross, dot, diff_angle import visual class Vector (object): """ A wrapper for visual.vector that expresses a cylinder via draw(), always pegged to the origin """ radius = 0.03 def __init__(self, xyz, color=(0,0,1)): self.v = vector(*xyz) self.xyz = xyz self.color = color self.cyl = None def draw(self): """define and render the cylinder""" self.cyl = cylinder(pos = (0,0,0), axis = self.v, radius = self.radius, color = self.color) def erase(self): """toss the cylinder""" if self.cyl: self.cyl.visible = 0 self.cyl = None def __repr__(self): return 'Vector @ (%s,%s,%s)' % self.xyz # some vector ops, including scalar multiplication def diff_angle(self, other): return self.v.diff_angle(other.v) def cross(self, other): temp = cross(self.v, other.v) return Vector((temp.x, temp.y, temp.z)) def dot(self, other): return dot(self.v, other.v) def __sub__(self, other): temp = self.v - other.v return Vector((temp.x, temp.y, temp.z)) def __add__(self, other): temp = self.v + other.v return Vector((temp.x, temp.y, temp.z)) def __mul__(self, scalar): temp = self.v * scalar return Vector((temp.x, temp.y, temp.z)) __rmul__ = __mul__ def __neg__(self): return Vector((-self.v.x, -self.v.y, -self.v.z)) def _length(self): return pow(self.v.x ** 2 + self.v.y ** 2 + self.v.z ** 2, 0.5) length = property(_length) class Edge (object): """ Edges are defined by two Vectors (above) and express as cylinder via draw(). """ radius = 0.03 color = (1,0,0) def __init__(self, v0, v1, color=None): if not isinstance(v0, Vector) or not isinstance(v1, Vector): raise TypeError("Wrong input types") if not color==None: self.color = color self.v0 = v0 self.v1 = v1 self.cyl = None def draw(self): """define and render the cylinder""" temp = (self.v1 - self.v0).xyz self.cyl = cylinder(pos = self.v0.xyz, axis = vector(*temp), radius = self.radius, color = self.color) def erase(self): """toss the cylinder""" if self.cyl: self.cyl.visible = 0 self.cyl = None def _length(self): return (self.v1 - self.v0).length length = property(_length) def __repr__(self): return 'Edge from %s to %s' % (self.v0, self.v1) def xyplotter(domain, f): """ domain should be an initialized generator, ready for next() triggering. f is any function of x. Consecutive Vectors trace connected edges. """ x0 = next(domain) y0 = f(x0) while True: x1 = next(domain) y1 = f(x1) e = Edge( Vector((x0, y0, 0)), Vector((x1, y1, 0)) ) e.draw() yield None x0, y0 = x1, y1 def axes(x=0,y=0,z=0): """ Draw some axes on the VPython canvas """ v0 = Vector((x,0,0)) v0.draw() v0 = Vector((-x,0,0)) v0.draw() v0 = Vector((0,y,0)) v0.draw() v0 = Vector((0,-y,0)) v0.draw() v0 = Vector((0,0,z)) v0.draw() v0 = Vector((0,0,-z)) v0.draw() def dgen(start, step): """ generic domain generator """ while True: yield start start += step def testme(): """ >>> from stickworks import testme Visual 2005-01-08 >>> testme() See: http://www.4dsolutions.net/ocn/graphics/cosines.png """ from math import cos def f(x): return cos(x) d = dgen(-5, 0.1) axes(-5,1,0) graph = xyplotter(d, f) for i in xrange(100): graph.next() def testmemore(): """ See: http://www.4dsolutions.net/ocn/graphics/pycalculus.png """ def snakeywakey(x): """ Polynomial with x-axis crossings at 3,2,-3,-7, with scaler to keep y-values under control (from a plotting point of view) """ return 0.01 * (x-3)*(x-2)*(x+3)*(x+7) def deriv(f, h=1e-5): """ Generic df(x)/dx approximator (discrete h) """ def funk(x): return (f(x+h)-f(x))/h return funk d1 = dgen(-8, 0.1) d2 = dgen(-8, 0.1) d3 = dgen(-8, 0.1) axes(-8,5,3) deriv_snakeywakey = deriv(snakeywakey) second_deriv = deriv(deriv_snakeywakey) graph1 = xyplotter(d1, snakeywakey) graph2 = xyplotter(d2, deriv_snakeywakey) graph3 = xyplotter(d3, second_deriv) Edge.color = (1,0,0) # make snakeywakey red for i in range(130): next(graph1) Edge.color = (0,1,0) # make derivative green for i in range(130): next(graph2) Edge.color = (0,1,1) # make 2nd derivative cyan for i in range(130): next(graph3) if __name__ == '__main__': testmemore()

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Quantities and Units in Python
by Vernon D. Cole 24 Sep '13

24 Sep '13

Given that my first useful programs were written to solve physics labs problems, this article jumped out at me, and I thought this group might find it useful. drdobbs.com/quantities-and-units-in-python<http://www.drdobbs.com/jvm/quantities-and-units-in-python/240161101> ( I know how much fun student can have with this sort of thing. One of those early labs had velocity stated in furlongs per fortnight. )

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Leveraging Python (recap of Djangocon workshop)
by Kirby Urner 19 Sep '13

19 Sep '13

Good recap of a lot of my old themes, repackaged for this flagship conference. I was an invited representative of the greater Python community helping Djangonauts (Djangstas <-- my preferred, if we're doing nicks) pick up some vibes from the Great Hall is it were (Vaults of Parnassus or whatever). I had a similar invited roll at a 'GIS in Action' one year, representing Python as "this other place" (near Programming Republic of Perl if you don't have your Atlas of Cyberia yet). Direct to Youtube: http://youtu.be/MH49zLTeQsE Blogged context: http://worldgame.blogspot.com/2013/09/leveraging-python.html I'm happy enough with it as a recap that it's my new Trailer for my Youtube channel. However there's more variety in that channel i.e. it's not the kind of trailer that shows a montage of all the best bits (too many spoilers in some previews). Kirby

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PYTHON for audio processing
by Sundeep Sivan 17 Sep '13

17 Sep '13

Hi, I am an M.TECH student. I would like to do my main project in python. and my main project is "Speaker recognition"(ie. recognizing persons from their voice). For feature extraction i would like to use MFCC(Mel frequency cepstral coefficients) and For feature matching i may use Hidden markov model or DTW(Dynamic time warping) or ANN. When i googled about it their are many toolkits like HTK etc avilable for MATLAB. But i didnt get any tools for python. So my question is that can i do my project in python? Also is their any toolkits or modules avilable for my project. Kindly help. Regards Sundeep

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Looking back on Chicago (Python workshop)
by kirby urner 09 Sep '13

09 Sep '13

I had a good workshop in Chicago. Two of the attenders worked assiduously on developing a native Linux installer for Visual Python (the latest) that wouldn't depend on Wine. The one guy brought his junky laptop (his "other" computer) and it overheated compiling all of wx (the latest Vpython integrates with wx). My schtick involves a mythical Python5, an add-on to my current courses, wherein we adopt a Model-View-Controller approach, as start with really simple views (i.e. ASCII art), knowing in advance the visualizations will be upgraded, using both render-time and real-time pipelines. The Model is of "tractors in a field", the controller being the user via interactive Python i.e. a very generic idea of MVC). Rather than sound too specialized and unable to talk about art or architecture, I focus on making this stuff friendly to humanities teachers, art and architecture teachers especially. The squares of our tractors' XY field could become hexagons and in 3D I mention the "octet truss" as good scaffolding (tetrahedrons + octahedrons), along with standard XYZ cubes. An ASCII character has "bit depth" (similar to "pixel depth") and with Unicode we go from 128 or 256 "colors" to "millions of colors" (an analogy with how our video displays evolved in a previous generation). The Unicode bridge takes me to both Russian and Chinese, where I mirror "tractor art" in various ways (North Americans were into tractors too). I did the slides in i-Movie and in true "bumbling professor" fashion needed audience participation to get the ball rolling, full screen etc. I invited other forms of audience participation and we did have some good conversations. They didn't want to "draw Django" though (I was inviting depictions of Django using imaginative graphics, versus a staid / stale "stack" -- the standard rectangular type "layered sandwich" of the engineering type magazines). Thanks to doing it in i-Movie, I should have a Youtube version shortly. It won't truly capture the talk, as I was also sampling other presentations when it came to Python5. Much of my content is autobiographical, but then I've been snaking around in Python world for awhile and have a good angle, my own front row seat (we all get one). I talk about various conferences, summits, meetings, meetups plus invite people to join us here on edu-sig. After the Monday workshop, I attended the speakers' dinner, hosted by PostgreSQL experts. The PostgreSQL community is quite fond of Django. The meal was in an Italian sports themed room and featured a full Italian meal, one of the top ten I've ever had (and that's from someone who lived in Italy for six years). The next day I took off on a pilgrimage to visit O'Reilly School's regional headquarters in Champaign-Urbana, hosted by a co-worker, and then to visit my daughter at her college in the neighboring state of Indiana. This was all by Alamo rental car, picked up and returned at O'Hare. Chicago is a fantastic city. Expensive though. I think the Django community will settle for a 2nd tier city next time. A luxury hotel right in downtown Chicago on Michigan Avenue, is one tough venue to pull off an event in, affordably. I was happy to take it in. Talking about art and architecture in Chicago makes so much sense, whereas the surrounding plains are all about rows and columns (of corn and soy), and tractors (and trains -- which are like tractors, but on tracks). Kirby

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