Mailman 3 January 2004 - Edu-sig

Re: [Tutor] what? (late nite entertainment) (*)
by Gregor Lingl March 25, 2005

March 25, 2005

Now: early morning corrections ... Alfred Milgrom wrote: > Hi Gregor: > > Hard to work out what is what :) as there seems to be a typo in one > line of your code: > > if x[z]: x[z*z:n:z]=y[z*z:n:z] > > (At least it doesn't work on my machine with Python 2.2) > Yeah, I had the idea when playing around with some new features of Python 2.3, as I do sometimes late at night - before shutting down my computer. This one I found at: http://www.python.org/doc/2.3.3/whatsnew/section-slices.html and I looked for an example for use of "assignment with extended slices" ... > Also the subroutine breaks for n = 1 or less. > Maybe you need a line at the start to say > if n <2 : return [0] > what() was intended to generate all primes less than n. (In fact it's an implementation of the sieve of Eratosthenes). The bugs came not only from not beeing interested in primes less than 2 ;-) but also from beeing a little tired already. Sorry. I think the following version repairs that - and hopefully uses less obfuscating variable names (which in fact originally was part of the "riddle"): def primes(n): sieve, zeros = range(n), [0]*n sieve[:2]= 0,0 i = 1 while i*i < n: if sieve[i]: sieve[i*i:n:i]=zeros[i*i:n:i] i += 1 return [p for p in sieve if p] Regards, Gregor >

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what? (late nite entertainment) (*)
by Gregor Lingl Jan. 29, 2004

Jan. 29, 2004

What is this? Another version of the well known ... def what(n): x,y = range(n), [0]*n x[1]= 0 z = 0 while z*z <= n: z+=1 if x[z]: x[z*z:n:z]=y[z*z:n:z] return [z for z in x if z] Regards, Gregor (*) at least in good old Europe

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Re: [Edu-sig] Itertools
by Dethe Elza Jan. 28, 2004

Jan. 28, 2004

On 27-Jan-04, at 5:41 PM, Kirby Urner wrote: >> count([n]) >> >> count will return consecutive integers until n is reached >> > > Actually, I think this one iterates *from* n. It has no stopping > parameter. You're right, I didn't skim closely enough. Thanks for catching that. --Dethe This past week, everyday when I opened my Wall Street Journal, I was met with a full page ad from Microsoft. This ad was dominated by three simple words "Protect your PC." This strikes me as something akin to the Saudi government running ads in the New York Times in mid-September of 2001 saying "Protect your Tall Buildings." --Russ McGuire

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Itertools
by Dethe Elza Jan. 28, 2004

Jan. 28, 2004

> Thanks for showing the islice trick. Have you made a study of > itertools? > I'd be interested in learning other such tips, if you've got the time. My pleasure. I'm really looking forward to Python 1.4 generator expressions, which will make the itertools module even more interesting. Calling generators is more efficient (down in the guts of Python) than calling functions, and because they are lazily evaluated, they tend to be more efficient in both memory and time than lists are, while maintaining much of the same ease of use. All of this is taken from the python docs, which covers all of the following functions and provides some useful examples. Like the fibonacci generator, many of these functions return an unbounded (infinite) number of results, and should only be used in functions, loops, or other iterators which truncate the stream somehow (like islice in the example). chain(iterable, [iterable,] ...) Chain takes a list of iterables and returns one which will iterate over the first iterable until it is exhausted, then the second until it is exhausted, and so on. count([n]) count will return consecutive integers until n is reached cycle(iterable) cycle will run through an iterable and save the values. When the iterable is exhausted it repeats using the saved values, turning a finite iterable into an infinite one. dropwhile(predicate, iterable) dropwhile is a latch function. It discards the results of the iterable as long as predictate(iterable.next()) returns true. Once the predictate becomes false it will return the rest of the results. ifilter(predicate, iterable) only returns iterable results for which the predicate is true. Equivalent to the builtin filter, but for iterables (and thus lazily evaluated) ifilterfalse(predicate, iterable) like ifilter but only returns iterator results for which the predicate is false imap(function, iterable [, iterable] ...) imap is like the builtin map function, but takes a list of iterables rather than a list of sequences, and applys the function to the results of the iterable(s) islice(iterable, [start], stop, [step]) islice takes a slice of an iterable, with optional start and step arguments. Because iterables can be infinite in length it does not permit negative numbers for stop, start, or step arguments. izip(iterable, [iterable], ...) izip is like the builtin zip function, but takes a list of iterables rather than sequences repeat(object, [times]) repeat returns an iterable which will return the same object over and over starmap(function, iterable) starmap is to imap as function(*args) is to function(a,b,c). It expects a tuple from the iterable, which is passed in as the args of function. takewhile(predicate, iterable) takewhile returns an iterable of the results of its iterable, truncated at the first result which evaluates false in the predicate function. All of that sounds very long-winded and obtuse perhaps. The basic concept is that rather than having a list, where all the elements of the list are known and can be manipulated, you have a stream and the elements can be manipulated as you receive them from the stream. I hope that's helpful. I'm willing to clarify any confusions I've created with it. --Dethe "Debugging is twice as hard as writing the code in the first place. Therefore, if you write the code as cleverly as possible, you are, by definition, not smart enough to debug it. " --Brian Kernighan

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Re: ..., closures, ...
by Jeff Sandys Jan. 27, 2004

Jan. 27, 2004

Kirby said: > Here's the same example in Python, in shell mode: > > >>> def newprint(x): > def anon(y): > print "%s, %s!" % (x,y) > return anon > > >>> h = newprint("Howdy") > >>> g = newprint("Greetings") > > >>> # Time passes... > > >>> h("world") > Howdy, world! > > >>> g("earthlings") > Greetings, earthlings! > > ======= > > I use 'anon' for anonymous function, but that's sort of an oxymoron, as > 'anon' is the function's name, insofar as functions have a name. If > you ask for string representations of these references, you get: > > > >>> g > <function anon at 0x0089A030> > >>> h > <function anon at 0x00ACEC70> > > If you want to make it clear in a different way, that these functions > are anonymous, you could use lambda like this: > > >>> def newprint(x): > def anon(y): > print "%s, %s!" % (x,y) > return lambda y: anon(y) > > >>> h = newprint("Howdy") > >>> g = newprint("Greetings") > >>> h > <function <lambda> at 0x00ACEB70> > >>> g > <function <lambda> at 0x00ACEE30> > > I guess I have no strong preference for either format. However, this > does show it's easy for lambda to represent functions of any length, > with print statements included. > Since lambda means anonymous you don't need to, def anon(y): >>> def newpr(x): ... return lambda y : "%s, %s!" % (x,y) ... >>> h = newpr("Howdy") >>> g = newpr("Greetings") >>> h("World") 'Howdy, World!' >>> g("earthlings") 'Greetings, earthlings!' >>> g <function <lambda> at 0x200f35b0> >>> h <function <lambda> at 0x200ecf70> Of course this method returns a string instead of printing the message. If you want to print the message you need to, def anon(x): because print is not a valid lambda expression (why?, I don't know): >>> def newprint(x): def newprint(x): ... return lambda y : print "%s, %s" % (x,y) File "<stdin>", line 2 return lambda y : print "%s, %s" % (x,y) ^ SyntaxError: invalid syntax >>> Closures are cool, Thanks, Jeff Sandys

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Re: [Edu-sig] Reversing dictionaries, closures, permutations etc.
by Terry Hancock Jan. 24, 2004

Jan. 24, 2004

On Friday 23 January 2004 07:50 pm, Kirby Urner wrote: > What I'm thinking about in this thread is a way to define functions and > inverse functions in a namespace, then pass them to a class P so that > operator overloading will allow: I have to confess that you lost me somewhere below this point (I'll reread it until I get it), but this is the sort of thing UserDict is for, right? I know Zope subclasses it to get the PersistentMapping class -- it gives you the basic dictionary interface, which you can then build on. Cheers, Terry -- Terry Hancock ( hancock at anansispaceworks.com ) Anansi Spaceworks http://www.anansispaceworks.com

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Re: Re: [Edu-sig] Python and Tk on MacOSX
by Kent Johnson Jan. 24, 2004

Jan. 24, 2004

There are instructions for building a binary distribution outlined in /Python-2.3.3/Mac/OSX/README and detailed in /Python-2.3.3/Mac/OSX/Dist/README.txt. I haven't tried it but they make it sound easy :-) The MacPython-SIG might be a better place to get help with this, that is where the MacPython pros hang out...I'm happy to help but I'm not an expert. I'm kind of surprised that there isn't a distribution available with Tk support. I think you are right that building from source is more than most Mac users would consider. Though maybe not such a stretch for a developer. Kent > By the way, can anyone tell me how to make a binary package of this once > I have it setup. It would be nice if I could just provide a Mac package > that does the install. My hunch is that most Mac users are not > accustomed to building from source. > > --John

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Python and Tk on MacOSX
by Kent Johnson Jan. 24, 2004

Jan. 24, 2004

OK, I'll take a stab at this. I just ran through this to upgrade from 2.3.1 to 2.3.3 (under MacOSX 10.2.6) so this should be pretty accurate... - Download and install TclTkAqua from http://www.maths.mq.edu.au/~steffen/tcltk/TclTkAqua/ I used the 8.4.4 Batteries Included installer but I only installed Tcl and Tk. The plain-vanilla TclTkAqua installer would probably be fine as well. - Download and uncompress the source distribution of Python, the one listed as "for Unix or OS X compile" - If you are building under MacOSX 10.2, you have to make a change to /Python-2.3.3/Mac/OSX/Makefile. Uncomment line 14 (remove the #) and comment line 16 (add a #) - In Terminal, enter the commands ./configure --enable-framework make sudo make frameworkinstall This should build /Library/Frameworks/Python.framework and /Applications/MacPython. At this point I can - run python and pythonw from Terminal as usual - Run PythonIDE (the Mac IDE) by double-clicking the launcher in the MacPython folder - Run IDLE by double-clicking the launcher in the MacPython folder (The IDLE launcher didn't work for me with 2.3.1. But the command 'pythonw idle' where idle is in the current directory, will worked for me to launch IDLE. Or just look at the idle file and type the two lines yourself.) Note that to run ANY Python GUI on MacOSX, you have to run with pythonw or PythonLauncher. HTH, Kent PS to John Zelle - your graphics.py works fine for me on MacOSX. >Jason (and other Mac users), > >I am very interested in helping folks get IDLE and my graphics >package running on the Mac with minimal hassles. I have seen >numerous references to the native Tcl/Tk and Python build under Aqua >(rather than using XDarwin), but I have not found either: >1) A binary package made available by someone who has done this to >make it easy for others to follow that route >or >2) Step-by-Step instructions for getting the build done right. > >I have built Python many times on Linux systems, but I have no Mac >experience. I do not even really know where to start. Do have >pointers to some resources that would allow less Mac-proficient >folks to get this done with a minimum of muss and fuss? > >By the way, I have also seen some references indicating that the >Tk-Aqua port may not yet be ready for primetime. Have you used your >setup enough to know how stable it is? > >--John > >Jason Cunliffe wrote: > >>>I have IDLE running on my Macs. I first installed Tcl/TkAqua, then rebuilt >>> >>> >>Python from source using the MacOSX instructions to do a framework build. >> >>I installed IDLE the same way about 6 months ago on Mac OSX 10.2 >>Was fairly painless. >> >>- jason >> >> >>_______________________________________________ >>Edu-sig mailing list >>Edu-sig(a)python.org >>http://mail.python.org/mailman/listinfo/edu-sig >> >> >> > >-- > John M. Zelle, Ph.D. | Wartburg College > Associate Prof. of CS | Dept. Math/CS/Physics >john.zelle(a)wartburg.edu | Waverly, Iowa > > > > >_______________________________________________ >Edu-sig mailing list >Edu-sig(a)python.org >http://mail.python.org/mailman/listinfo/edu-sig -- Kent S Johnson http://www.kentsjohnson.com

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Re: Re: [Edu-sig] HS Example problems
by Kent Johnson Jan. 24, 2004

Jan. 24, 2004

If you use the MacPython installer it should include the MacPython IDE out of the box. I have IDLE running on my Macs. I first installed Tcl/TkAqua, then rebuilt Python from source using the MacOSX instructions to do a framework build. You might have better luck with this question on the MacPython mailing list. Kent > >On another note: > >I am using OSX 10.2 and am having problem setting up the computers to run a > >decent IDE. I have tried MacPython and Pyoxide. Any help would be deeply > >appreciated. > >

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HS Example problems
by mhanna＠pvcsd.org Jan. 23, 2004

Jan. 23, 2004

Hello all, I am new to the list and Python in general. I want to start using Python in my Into to CS Class in High School. I have previewed a number of books but am having difficulties finding a decent source for: 1) a detailed curriculum (basic class for 100% new programming students) 2) Good examples and problems for projects On another note: I am using OSX 10.2 and am having problem setting up the computers to run a decent IDE. I have tried MacPython and Pyoxide. Any help would be deeply appreciated. Thanks, Mike Hanna

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