🌐 Mailman 3 August 2007 - Python-list - python.org

general function for sorting a matrix
by Xah Lee Sept. 10, 2007

Sept. 10, 2007

A couple years ago, i posted a programing problem, about writing a function that will sort a arbitrarily dimentioned matrix in any possible way to sort it. Such a function, is rather typical in functional programing languages. I wrote a version in 1999 in perl for practical purposes, since sorting a matrix (i.e. list of lists) is rather common. With this function, i can have a single interface to deal with any list (including list of lists). It is ideal, that a language's function for sort actually are of this generality. (See “What is Expressiveness in a Computer Language”, Xah Lee, 2005. http://xahlee.org/perl-python/what_is_expresiveness.html ) The advantage of such a generality, is that a programer don't need to write a sorting code every time she encounters a list. Anyway, so i wrote it in 1999 in perl for practical purposes, and have used it in industrial coding often. In 2005, while i was learning Python, i wrote a python version as a exercise. Today, i actually need it again, while coding in python. So i looked at my code and spruced up the documentation. Here's the function spec: ---------------- Today we'll write a function that can sort a matrix in all possible ways. Following is the specification. Take a day to see if you can write such a function in your favorite language. Perl and Python solutions are at the end of this page. sort_matrix( matrix, [[n1, s1, d1], [n2, s2, d2], [n3, s3, d3], ...]) returns a sorted matrix by n1 th column, if tie, then by n2 th column ... and so on. The first argument is a list, whose elements are lists of equal lengths. s1, s2, s3... are booleans. If True, then the corresponding column are interpreted as a string and the ordering is lexicographical. d1, d2, d3... are booleans. If True, the sort for the corresponding column are ascending. Example:. myMatrix = [ [3, 99, 'a'], [2, 77, 'a'], [1, 77, 'a'] ]; sort_matrix(myMatrix,[[3,True,True],[2,False,True]]) This means sort by 3th column, regarding it as strings, and in ascending order. If tie, sort by 2th column, regarding it as number, in ascending order. It returns: [[2,77,'a'], [1,77,'a'], [3,99,'a']] ---------------- While reviewing this code, there's something interesting of note. Namely, in my perl solution, the approach is drastically different than the python version. Instead of sorting by looping thru the sorting directives, it parses the directives then generate the complete sort code, then eval it in one shot. This is more of a pure functional approach. I thought it is of interest. The Perl and Python solutions are at: General Function For Matrix Sorting http://xahlee.org/perl-python/sort_matrix.html It would be interesting, to see a python version using the approach i've done in the Perl version, and a Perl version using imperative approach without using eval(). A solution in lisp (emacs lisp, common lisp, scheme) would be relatively trivial, similarly for Haskell and Mathematica. In fact, i think the sort function as specified above are not very useful in practice in these languages to various degress (depending on the lang). Because a functional language usually have powerful, generalized functions and constructs that solve the above in a few trivial lines that are rather ideomatic to the language. Nevertheless, it would be interesting to see a solution in the above languages. For the languages i'm personally involved, a major difficulty would be Java. In my opinion, it would be a very difficult (if not impossible) to construct this sort function Java, C, C++, C#. Xah xah(a)xahlee.org ∑ http://xahlee.org/

4 4

Re: Does shuffle() produce uniform result ?
by tooru honda Sept. 10, 2007

Sept. 10, 2007

Hi, First of all, my thanks to all of you who replied. I am writing a gamble simulation to convince my friend that his "winning strategy" doesn't work. I use shuffle method from a random.SystemRandom instance to shuffle 8 decks of cards. As the number of cards is quite small (number of cards is 416), the nonuniformity doesn't matter as most of you have already said. Just to avoid argument from my friend, I am considering writing my own randint and shuffle methods based on os.urandom() though. -tooru honda

7 22

Re: What does this thread have to do with classical music,
by ah Sept. 8, 2007

Sept. 8, 2007

Art Deco wrote: > ah <splifingate(a)gmail.com> wrote: >>Art Deco wrote: >>> ah <splifingate(a)gmail.com> wrote: >>>>Art Deco wrote: >>>>> Who wrote? >>>>> >>>>> >>>>>>What does that have to do with classical music, snuhwolf? >>>>> >>>>>>What does that have to do with classical music, snuhwolf? >>>>> >>>>> How many more times will you be asking the same tired, lame questions, >>>>> Tholen? >>>> >>>>Till 2056? >>> >>> At that point, he will have made the Thirty Years Pset War look like >>> 1967 in the Sinai. >> >>It must have been Hell to keep a garden during those times. >> >>Did they all eat jerky, or what? > > Worse -- worm-laden hardtack. Luxury! Why, I remember when I was a lad . . . we used to watch the local churls across the fences eating that well. We only had millings (and (occasionally) water) on Tuesdays and Fridays.

2 9

platform system may be Windows or Microsoft since Vista
by p.lavarre＠ieee.org Sept. 7, 2007

Sept. 7, 2007

Let's suppose you get Python for Vista Windows today from http://www.python.org/download/. Should you then conclude that the tests: if platform.system() in ('Windows', 'Microsoft'): if not (platform.system() in ('Windows', 'Microsoft')): are now exactly what you should write for that 2.5.1 Python, when you must resort to os-specific tools like DeviceIoControl, in place of the slightly simpler tests that worked before: if platform.system() == 'Windows': # Microsoft if platform.system() != 'Windows': # Microsoft ? Curiously yours, thanks in advance, P.S. Groups search assures me clp hasn't previously reviewed: platform system Windows Microsoft P.P.S. I ask because this August I rediscovered this 28 May Python uname vs. Win kernel32.getVersionEx issue indexed by Google as follows: http://mail.python.org/pipermail/patches/2007-June/022947.html ... Patches item #1726668, was opened at 2007-05-28 03:23 On Microsoft Vista platform.system() returns 'Microsoft' and platform.release() returns 'Windows' Under Microsoft Windows XP SP2 platform.system() returns 'Windows' and platform.release() returns 'XP'. This is problem was caused by a change in the output of the "ver" command. In Windows XP SP2 "ver" outputted 'Microsoft Windows XP [Version 5.1.2600]' In Microsoft Vista "ver" outputted 'Microsoft Windows [Version 6.0.6000]'. The lack of the 3rd word before version causes _syscmd_ver(...) in platform.py to return 'Microsoft' for system instead of 'Microsoft Windows'. This causes uname() to return the incorrect values. Both system() and release() call uname(). ...

3 4

reload(sys)
by Sönmez Kartal Sept. 6, 2007

Sept. 6, 2007

Hello, I've had an encoding issue and solved it by "sys.setdefaultencoding('utf-8')"... My first try wasn't successful since setdefaultencoding is not named when I imported sys module. After, I import sys module, I needed to write "reload(sys)" also. I wonder why we need to call "reload(sys)" to get setdefaultencoding named? Happy coding

4 11

Let's Unite Against Jews and Mongrels!
by Nenad Milicevic - The Aryan Serb Sept. 5, 2007

Sept. 5, 2007

Rise up and shine, white sons and daughters Rise up and shine, you gotta fight to part those waters When we swim in the light, all will be okay The black, yellow and brown man will wash away. ------------------------------ Let's break the chains of Jewish and black domination! Unite, white brothers and sisters, and let's defeat those who oppress our white heritage! Our skin is our uniform! Serbian Committee for Aryan Defence Nenad Milicevic, executive Usenet name: Raoul Endymion or Raul Endymion ICQ 208030128 endymion(a)deadspam.com endimion(a)myrealbox.com Belgrade, Serbia

10 10

Registering a python function in C
by fernando Sept. 5, 2007

Sept. 5, 2007

Could someone post an example on how to register a python function as a callback in a C function? It expects a pointer to PyObject... how do I expose that? Basically, the signature of the function is foo(PyObject* obj), where obj is the callback function... It's not exactly extending or embedding, I've looked at those examples but they don't really show how to do this... Thanks for the help!

5 7

list index()
by zzbbaadd＠aol.com Sept. 4, 2007

Sept. 4, 2007

What's with the index() function of lists throwing an exception on not found? Let's hope this is rectified in Python 3. If nothing else, add a function that doesn't throw an exception. There are a million situations where you can have an item not be in a list and it is not an exception situation.

18 37

Does shuffle() produce uniform result ?
by tooru honda Sept. 4, 2007

Sept. 4, 2007

Hi, I have read the source code of the built-in random module, random.py. After also reading Wiki article on Knuth Shuffle algorithm, I wonder if the shuffle method implemented in random.py produces results with modulo bias. The reasoning is as follows: Because the method random() only produces finitely many possible results, we get modulo bias when the number of possible results is not divisible by the size of the shuffled list. 1. Does shuffle() produce uniform result ? 2. If not, is there a fast and uniform shuffle() available somewhere ? Thanks ! -tooru honda

7 7

Creating a multi-tier client/server application
by Jeff Sept. 4, 2007

Sept. 4, 2007

Hello everyone. I've searched through the archives here, and it seems that questions similar to this one have come up in the past, but I was hoping that I could pick your Pythonic brains a bit. Here's a broad overview of what I need to do: cross-platform, client- side GUI apps that interact with a server backed by a database. I'd also like the possibility of having a web interface for small portions of the app. It will be a fairly complex system for managing personnel (and training, performance reviews, etc.) and payroll, and I will probably have about a year or more to write it. None of this is written yet--actually, it's not even to the point of specs yet, I'm just trying to learn the best way to do this *before* I get to the specs. I want to plan this application out as thoroughly as possible before writing any code, and I want to do it The Right Way(TM), hence I have (hopefully) convinced my manager (and clients) that Python is the way to go. I have a couple years of experience in Python, but it's mostly been web apps (which I am thoroughly sick of making, thanks to PHP) and simple CLI programs. Not sure if any of that information helps, but I'm tired, so please bear with me. The application definitely needs at least three tiers: client, server, and DB. I want as little logic in the client as possible (if not none), as there will be sensitive data in the DB. I also can't have the clients connect to the DB directly, as it will need to only accept connections on the local host. The client will probably be installed on 50-100 machines, and will be used by several hundred people (yes, they're sharing machines--the users will be computer lab consultants/ server operators/helpdesk employees, etc. and their supervisors), so authentication (using LDAP) and authorization (using groups I will define) will be very important. Also important will be automatic updates of the client, which I figure I'll do by comparing version numbers, then downloading an archive (egg, maybe?) of the latest (compiled? byte-?) code. I will probably make the GUI in wxPython, as that seems to be most flexible and nicely cross-platform choice--but I am open to suggestions. Not too worried about that one, though. For the database, I'll use Postgres, because I love Postgres. Probably not going to budge on that one unless anyone has any good reasons to. I'd also like to use SQLAlchemy (because it is so nice), but this is not a requirement (I can write SQL, but... SQLAlchemy is so nice.) I'd like to use an ORM mainly because it would facilitate code reuse for the (very simple) web interface, and other offshoot tools down the line. So, my real question (sorry for the all the exposition) is this: how to do the networking? I'd really like to have the client send a simple request to the server along the lines of "fetch this (or these) object(s)", or "update this value in this object", then let the server decide if the user actually is allowed to do so, and then make the change in the database. My first thought was XML-RPC, because I've used it before, and it is so nice and clean--but then I can't send objects, which is really rather crucial. Then I looked at Pyro, which seems awesome, but I'm confused as to how (if possible) I would use it with a DB. Would I have to figure out on the client what SQL query to send to get the right objects? That would kind of kill the separation of logic. And would it work at all with SQLAlchemy (or any ORM for that matter)? I looked at SOAP. It made me feel unclean. I looked at some CORBA, at which point my eyes glazed over (possibly not CORBA's fault, I will look at it again later). I checked out Twisted, but there are so vastly many parts to it, that I'm not sure where to even start. I'm not ruling out writing my own simple protocol, but it seems like I'd be reinventing a wheel that's already been reinvented countless times. So, all that said--any advice on how to do the networking? And on the auto-update? For that matter, any advice on anything I've mentioned (or haven't?) Please feel free to ask me to clarify anything, or tell me if I'm being an idiot about anything. Thanks, Jeff

9 19