Mailman 3 May 2001 - Edu-sig

An intro without objects??
by Kirby Urner 28 May '01

28 May '01

In the chapter entitled 'Building Abstractions with Data' in 'Structure and Interpretation of Computer Programs', the rational number object is introduced (Sec. 2.1.1.)... http://mitpress.mit.edu/sicp/full-text/book/book-Z-H-13.html ... except not as "objects", but in terms of procedures and data, with the data structure in question being the "pair" i.e. a (numerator, denominator) tuple, with relevant procedures for forming such pairs (cons) and extracting either (car, cdr). What you're left with is a sense of data on the one hand, and procedures for operating on that data on the other. I miss the higher level abstraction of "object", in which the relevant procedures are encapsulated, along with the data structure, such that our interface to the "rational number object" contains whatever functionality we like. Plus I miss the ability to easily override primitive operators, such that I can multiply, add, subtract rational numbers (a.k.a. fractions) using *, + - etc. This is an important abstraction in math -- to realize that these operators may be redefined at will (yet usually according to various rules of group theory, e.g. whatever * means, there should be an identity object ident such that anyobj * ident = anyobj = ident * anyobj). In the Python approach, we might begin in the "wishful thinking" stage by sketching out a shell object: class Rat: def __init__(self,p,q): self.numer = p self.denom = q def __add__(self,other): pass def __sub__(self,other): pass def __mul__(self,other): pass >>> a = Rat(2,3) >>> a.numer 2 >>> a.denom 3 and so on. We'll also want to have a way of representing rational numbers to the screen, along the lines of: (define (print-rat x) (newline) (display (numer x)) (display "/") (display (denom x))) i.e. def __repr__(self): return "%s/%s" % (self.numer,self.denom) >>> a = Rat(2,3) >>> a 2/3 And so on. I prefer this approach, because we're setting up a class definition, not a sandbox of procedures and data, with the procedures tied to the data simply by the programmer's knowledge and/or by documentation. The class definition is itself a kind of data structure, in that it files the relevant methods with the data, under the same heading. No one has to keep track of what procedures "belong" with what data. That's built in to the class definition. Furthermore, we're setting up an inheritable framework. A subclass could pick up where Rat leaves off, and further elaborate methods -- perhaps it would simply have a different representation scheme, outputting "mixed" fractions e.g. 5 1/4 instead of 25/4. This is commonly done with a global variable switch, but a subclass would work. In the case of Matrices, any ol' Matrix object would by nxm, with a subclass, Sqmatrix, being for nxn or square matrices -- where only these latter have certain methods, such as determinant and inverse. I guess I'm feeling uneasy with a foundational approach that doesn't bring in the concept of objects closer to the beginning. The object concept is an important one. Just procedures and data, without objects, seems a rather scattered/cluttered approach. Shouldn't newcomers learn the object model right about where this rational numbers example is presented? Certainly building rational numbers as objects would be a standard exercise in a Python-focused curriculum (might be a math class -- if the distinction matters). Kirby

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Python accessibility
by Brent Burley and Pat Erb 28 May '01

28 May '01

Python is a very accessible (and very capable) language. However, if you don't have Python on your system, it's not very accessible, and if you don't have an Internet connection, you're out of luck. Even if you have a broadband connection, you have a lot of work ahead of you, far more than most people (in the CP4E sense) are willing or capable of doing. I recently made a Python CD-ROM for my nephew since he has no Internet access at home. It was a lot of work gathering and assembling the pieces and I was only able to include a fraction of what I had hoped due to lack of time. I would LOVE to see someone sell a "Python EDU-SIG Resources CD" via mail order. I think it would make a great school project (hint hint) and could earn some extra money for the school. I'd love to see the disc full of all the stuff that's been advertised on edu-sig - VPython, Alice, PyGame, Jeff's book, Kirby's math stuff, etc., and I'd love to see it constantly updated. Heck, I'd buy a subscription! I would hope something like this could sell for under $10 including S+H. After all, the cost of materials and postage should be less than $1. And I would hope the license would allow free duplication of the CD. Teachers should be able to give a copy to every student in the class for the cost of a CD-R blank and the time of a T/A. Thoughts? Or more importantly, volunteers? Brent Burley

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Writing a web server
by Brent Burley and Pat Erb 28 May '01

28 May '01

One of the things that is _really_ easy to do in Python is writing a web server. In fact, the standard distribution comes with a fully functioning server as an example. Find your lib directory and run SimpleHTTPServer.py directly and then open http://localhost:8000/ in your web browser. This web server provides a simple server-side file browser that can navigate directories and serve up html, graphics, and text files. This should work on most computers, including Windows, and you don't even need an Internet connection. Try it! I've attached an even simpler web server (16 lines of code) that is the web equivalent of "hello world". As simple as it is, it's complete enough that it shows everything you need to build a dynamic website. Just send "text/html" instead of "text/plain" and generate an html file dynamically in the do_GET method. The "self.path" variable contains the requested URL and can encode any information you want to pass between requests. How's this for a possible 9th/10th grade course: * Web Programming with Python - Students will program a fully-functioning website from scratch. Students will choose from building an interactive storybook where the reader influences the outcome of the story, or a web-community site with a message board and voting booth. No prior programming experience necessary. I think there are many advantages to this approach. For one thing, students can get immediate feedback through the web browser and can easily include graphics, sound, and simple user-interfaces via html forms. If the school allows the projects to be posted to a public server, then the students' work could be shown off to friends, relatives, and the world at large. This teaches directly marketable, real world skills and teaches programming as a means to an end. I also have an inkling (based on my niece and her friends) that this would appeal strongly to girls. Thoughts? Brent Burley

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Lisp vs Scheme vs Python
by Matthias Felleisen 26 May '01

26 May '01

Kirby writes: I did study the Lisp example for awhile. I'm always awed by LISP and all that tail recursion. Yet the LISP _does_ have looping syntax in the versions I've seen. It's Scheme that stays purist about using only recursion for looping, no? Lisp is _not_ tail-call optimizing by standard, and indeed, I don't know of a Lisp implementation that performs tail-call optimizations. Scheme is tail-call optimizing by standard, though there are implementations that break tail-call optimizations. As a result, there is no _need_ for looping constructs in Scheme yet there is a need for such beasts in Lisp. In that reagrad, Lisp and Python are quite similar. Of course, "need" does not imply that Scheme doesn't provide a looping construct. As a matter of fact, the language includes a do macro for just that purpose. The problem with forcing looping constructs is that they force programmers to produce code whose structures doesn't match the structure of the data. If you look at the definition of NAT, you see linear induction. A linear recursion in code matches this definition. If you look at the definition of LIST you see ... and so on. Python and Lisp fail programmers in that regard. With Python and Lisp you must teach kids "look at this example, modify it, follow my suggestions" and hope that it eventually clicks. Of course, the interactive nature of Lisp's evaluator (since 1958?) and of Python's interactive REPL (uh, IDLE, since 1995?) help students explore quickly and absorb these micro patterns. Still, in the end if they are confronted with an unusual data class, they fail to come up with code. I tested dozens and hundreds of students on that. They all had introductions in Pascal or C (min 1 year) and couldn't write a function that traversed a non-standard data class if their life depended on it. -- Matthias Matthias Felleisen Professor of Computer Science Northeastern University, Boston Rice University, Houston For a new way to look at the world of high school computing, see http://www.teach-scheme.org/ http://www.htdp.org/ "Computer Science is no more about computers than astronomy is about telescopes." -- E. W. Dijkstra

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Learning Python in pairs
by Timothy Wilson 26 May '01

26 May '01

I'm watching a RealVideo interview with Bob Martin, author, consultant, and chief promoter of the Extreme Programming methodology. *I am not a professional software developer*, but I find the collaborative nature of the process intriguing. I'm going to have two sections of about 25 students each next fall and I have a lab with 30 computers. I'm intrigued by the idea of having the students work in pairs. (This is something we science teachers are very comfortable with.) Do any list subscribers have any thoughts about solo vs. paired learning in a programming class? -Tim -- Tim Wilson | Visit Sibley online: | Check out: Henry Sibley HS | http://www.isd197.org | http://www.zope.org W. St. Paul, MN | | http://slashdot.org wilson(a)visi.com | <dtml-var pithy_quote> | http://linux.com

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The Programmers Stone
by Roman Suzi 26 May '01

26 May '01

Hello! Probably I am not original, but I think this is very important for cp4e philosophy: http://www.reciprocality.org/Reciprocality/r0/index.html It actually says WHY cp is not 4e and WHAT to do. I recalled the progstone because it's very essential to the problem of cp4e: only Mappers could _program_ what they want, Packers just recall instructions to do something and have trouble when they aren't available in their memory, local library or the Internet ;-) Roman Suzi Sincerely yours, Roman Suzi -- _/ Russia _/ Karelia _/ Petrozavodsk _/ rnd(a)onego.ru _/ _/ Saturday, May 26, 2001 _/ Powered by Linux RedHat 6.2 _/ _/ "Women do come with instructions; ask them." _/

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Re: [Edu-sig] Python for Fun
by Chris Meyers 26 May '01

26 May '01

05/25/2001 1:55:29 PM, Kirby Urner <pdx4d(a)teleport.com> wrote: Hi Kirby, We're still on Python 1.5.3 mainly because we have so much code in running systems that upgrading involves a lot of regression testing. Try for this summer for sure. Lots of stuff out there that assumes 2.0 as a base. Zope, Vpython, wxPython, etc. A year ago we upgraded from 3.0 and had some glitches - mostly with comparisons where one value was None. >Just for fun: tweaking logic.py Connector class with 2.1 idioms: > > def connect (self, inputs) : > if type(inputs) != type([]) : inputs = [inputs] > self.connects += inputs # <-- here > This is a nice new feature (+= etc.). Does it save time and evaluate the left hand address only once? Or is it just syntactic sugar? If the calculation is complex, it can make a real difference in program speed. Like array[n][nextSlot(whatever)] += 1 Or in our case we are very often incrementing (or the like) an object attribute, which is a really a dict lookup. Don't want to do the lookup twice. > def set (self, value) : > if self.value == value : return # Ignore if no change > self.value = value > if self.activates : self.owner.evaluate() > if self.monitor : > print "Connector %s-%s set to %s" % \ > (self.owner.name,self.name,self.value) > [con.set(value) for con in self.connects] # <-- and here > This should also save time, I would think, since the list is not constantly resized? Can't test it. Don't work on 1.5.3 > >Could also go: > > self.connects.extend(inputs) (is that 1.5 or later?) > Is this actually different from .append ? > >I find it interesting that you can define lists simply for >their side-effects, with the list itself saved nowhere. Indeed, >you can stick [1,2,3] (no assignment to a variable) anywhere >a method and nothing happens -- __repr__ isn't triggered >except at the command line. > That's kind of cool. I had never tried it. Replace 1,2,3 with function calls and off they go, left to right. This reminds me of the old Lisp "PROG" that would evaluate its arguments just for the side effects. >I did have > > map(lambda con: con.set(value), self.connects) > >which makes use of nested scopes (value in lambda is getting a >pointer from the surrounding method), but list comprehension >doesn't see this as a case of scope nesting i.e. variables >within the brackets are locally scoped already. > I tried this and it seemed to work >>> >>> class con : ... def __init__ (self) : ... self.x = 5 ... def prnt (selfi,c) : ... print self.x + c ... >>> a = con() >>> b = [a,a,a] >>> map(lambda x: x.prnt(4), b) 9 9 9 [None, None, None] >>> Speaking of scoping. If you get around to Lisp in Python, there's a section on dynamic scoping with an example. Chris

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RE: [Edu-sig] Python for Fun
by Chris Meyers 25 May '01

25 May '01

Hi Allen, I think I need to learn at lot more about Zope. Most of what we're doing here involves a marriage between database tables and Python dictionaries turned into objects. We made a small extension to the Sybase module to retrieve data from SQL queries, mold them into dictionarys, and attach as attributes to created objects. It was technology that was effective even 5 years ago. I don't have much to offer for teaching yet. But I'll try to keep track this summer. Syllabus, what works, what dont. I assume you've seen Jeff Elkners book at www.ibiblio.org/obp and projects his high school class is doing. Chris 05/25/2001 12:12:24 PM, "Schmidt, Allen J." <aschmidt(a)nv.cc.va.us> wrote: >Hi Chris! > >I too work for a newspaper - The Free Lance-Star - in Fredericksburg, >Virginia (www.fredericksburg.com). We are using Zope mixed with Python, XML >and SQL to handle the automated production of our paper online. Working out >very well and having a great time with Zope! Made our jobs a lot easier. > >Would love to hear of anything you can offer for teaching Python. We are >Zopeheads here and some are more versed in Python than others...only using >it for things we need to for interactiion in Zope. > >Trying to get a curriculum for teaching younger students (8-14) for our home >schooling computer classes. > >Allen Schmidt >aschmidt(a)fredericksburg.com >

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RE: [Edu-sig] Python for Fun
by Schmidt, Allen J. 25 May '01

25 May '01

Zope works great in the newspaper business. The stories come from the print-side database as XML files and the whole lot is FTPd up to our server overnight. An automatic script runs in the early morning to run through each story, grab the properties of each (and any photos attached to the story) add them into the Zope database and catalog each one. The the catagories are pulled out and they are organized into groups; localities, sports, obits, etc. Then when they are in, another script runs and the catalog index is built which is what you see on our front page. All(most) is automatically done - a process that used to take a guy all night to do by hand dealing with static text files. Zope is a great tool and fun too! Changes all the time and we keep bolting on new stuff. Yes, please let me know how your courses go! Good luck! Allen -----Original Message----- From: Chris Meyers To: Schmidt Allen J.; 'Chris Meyers '; 'edu-sig(a)python.org ' Sent: 5/25/2001 5:33 PM Subject: RE: [Edu-sig] Python for Fun Hi Allen, I think I need to learn at lot more about Zope. Most of what we're doing here involves a marriage between database tables and Python dictionaries turned into objects. We made a small extension to the Sybase module to retrieve data from SQL queries, mold them into dictionarys, and attach as attributes to created objects. It was technology that was effective even 5 years ago. I don't have much to offer for teaching yet. But I'll try to keep track this summer. Syllabus, what works, what dont. I assume you've seen Jeff Elkners book at www.ibiblio.org/obp and projects his high school class is doing. Chris 05/25/2001 12:12:24 PM, "Schmidt, Allen J." <aschmidt(a)nv.cc.va.us> wrote: >Hi Chris! > >I too work for a newspaper - The Free Lance-Star - in Fredericksburg, >Virginia (www.fredericksburg.com). We are using Zope mixed with Python, XML >and SQL to handle the automated production of our paper online. Working out >very well and having a great time with Zope! Made our jobs a lot easier. > >Would love to hear of anything you can offer for teaching Python. We are >Zopeheads here and some are more versed in Python than others...only using >it for things we need to for interactiion in Zope. > >Trying to get a curriculum for teaching younger students (8-14) for our home >schooling computer classes. > >Allen Schmidt >aschmidt(a)fredericksburg.com >

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Python for Fun
by Chris Meyers 25 May '01

25 May '01

Hi, I would like to introduce myself and offer my first posting to the group. My name is Chris Meyers and I've been working with Jeff Elkner and his Python class at Yorktown High School on the Open Book Project. I'm working primarily on Python case studies for intermediate students. The first 4 (of hopefully a dozen) can be found at www.ibiblio.org/cmeyers. These programs are some of my favorites from many years of programming. They are all short, just a page or two but should demonstrate good use of recursion and objects with algorithms that are a little beyond the ordinary. You will be led to a writeup that should explain the code in detail. These 1st 4 are Logic Circuits. Simulation of logic gates with object classes that make good use of inheritance. This study starts with AND, OR, NOT gates and builds up to a four-bit binary adder. Several students are extending this study at Yorktown. Lisp in Python. A study of the classic evalquote mechanism. We end up with an interactive lisp similar to interactive python. Tower of Hanoi. A reworking of the standard algoritm to use objects sending messages. Includes a classroom exercise where students play the objects User Input. An extension of raw_input and input functions to provide a scripting mechanism. Used by Lisp in Python to load files. I've been a programmer for nearly 30 years, and have used a lot of languages. I work at the daily newspaper in Eugene Oregon, the Register Guard. I found Python about 5 years ago and tried it on a text processing project and it worked so well we've never looked back. Now 8 people program with it daily, and it is absolutely the language of choice for all new projects. The production of our internet newspaper is automated with Python code to the extent that it requires only about 1.5 hours a day for someone to produce. You can see it at www.registerguard.com. We are converting all of our old systems on VAX computers to Unix using Python and SQL. 2 years ago we converted our circulation system from Cobol to a combination of VB, Python, and SQL. The amount of code was reduced a factor of six, the system runs well, changes are easy, everyone is happy. On a personal note, I've really grown to love this language (Thanks Guido!!) Lots of reasons, but you all know them and I would be just preaching to the choir. Assuming we get enough students (and I'm getting a lot of interest) I'll be teaching a beginning Python class at our community college this summer. It's short, only 15 hours. But it will be mostly adults and should be interesting to see how far we get. Thanks, Chris

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