Pygame.draw challenge is over!
It was quite successful too! Download the submissions from the pyweek.org site: http://media.pyweek.org/static/pgd-200606.zip Congratulations to all who participated! Richard -- Visit the PyWeek website: http://www.pyweek.org/ -- http://mail.python.org/mailman/listinfo/python-announce-list Support the Python Software Foundation: http://www.python.org/psf/donations.html
Re: MSoffice metadata
[EMAIL PROTECTED] wrote: hi is there a module in Python to extract metadata in MS office documents thanks Perhaps. OpenOffice can read and write MS office files, and OpenOffice has an API (called UNO for Universal Network Objects) which has a Python binding (called the Python-UNO bridge). This might (eventually) get you what you want. Here's a URL for it: http://udk.openoffice.org/python/python-bridge.html Good luck, Gary Herron -- http://mail.python.org/mailman/listinfo/python-list
Re: subprocess.Popen on Windows
Hi, Been there - try looking at: http://groups.google.com/group/comp.lang.python/browse_frm/thread/f2cb83e948326ff5/d69feabbfc940b01?q=uri.nixrnum=2#d69feabbfc940b01 Cheers, Uri -- http://mail.python.org/mailman/listinfo/python-list
Re: String negative indices?
On Sat, 24 Jun 2006 21:15:17 -0700, Erik Max Francis wrote: Steven D'Aprano wrote: In mathematics, well, maybe... certainly in the Real number system, there is no difference, and +0 and -0 are just two ways of writing the same thing. In the hyperreals, +0 and -0 are the same, but there are infinitesimals which are different, and signed. I don't know enough about the surreals to comment. In matrix maths, there are an infinite number of different matrices where all the elements are zero -- they are all distinct, different, zeroes. What do you even mean by that? By matrix maths, do you just mean matrices whose elements are reals, or something else? Given any matrix M, there is a matrix Z such that M+Z = M. That matrix Z is equivalent to zero in the reals, where x+0 = x. In the reals, there is only one zero, 0. In matrices, there are an infinite number of zeroes: 1x1 matrix: [0] 1x2 matrix: [0 0] 1x3 matrix: [0 0 0] 2x2 matrix: [0 0] [0 0] etc. It is true that none of these are exactly equivalent to +0 and -0, but my point was that there can be more than one distinct zero in pure mathematics, and there is nothing wrong with the concept of a system with more than one distinct zero. -- Steven -- http://mail.python.org/mailman/listinfo/python-list
Re: What is Expressiveness in a Computer Language
On 22 Jun 2006 08:42:09 -0700, [EMAIL PROTECTED] wrote: Darren New schrieb: I'm pretty sure in Pascal you could say Type Apple = Integer; Orange = Integer; and then vars of type apple and orange were not interchangable. No, the following compiles perfectly fine (using GNU Pascal): program bla; type apple = integer; orange = integer; var a : apple; o : orange; begin a := o end. You are both correct. The original Pascal specification failed to mention whether user defined types should be compatible by name or by structure. Though Wirth's own 1974 reference implementation used name compatibility, implementations were free to use structure compatibility instead and many did. There was a time when typing differences made Pascal code completely non-portable[1]. When Pascal was finally standardized in 1983, the committees followed C's (dubious) example and chose to use structure compatibility for simple types and name compatibility for records. [1] Wirth also failed to specify whether boolean expression evaluation should be short-circuit or complete. Again, implementations went in both directions. Some allowed either method by switch, but the type compatibility issue continued to plague Pascal until standard conforming compilers emerged in the mid 80's. George -- for email reply remove / from address -- http://mail.python.org/mailman/listinfo/python-list
Re: String negative indices?
Steven D'Aprano wrote: Steven D'Aprano wrote: In matrix maths, there are an infinite number of different matrices where all the elements are zero -- they are all distinct, different, zeroes. What do you even mean by that? By matrix maths, do you just mean matrices whose elements are reals, or something else? Given any matrix M, there is a matrix Z such that M+Z = M. That matrix Z is equivalent to zero in the reals, where x+0 = x. Ah, of course. I knew this, I just misinterpreted your distinct, different, zeroes as referring to the elements but not the matrices. Just a misunderstanding. Every zero matrix is an additive identity, and there are an infinite number of them. That's certainly true. -- Erik Max Francis [EMAIL PROTECTED] http://www.alcyone.com/max/ San Jose, CA, USA 37 20 N 121 53 W AIM erikmaxfrancis There's a reason why we / Keep chasing morning -- Sandra St. Victor -- http://mail.python.org/mailman/listinfo/python-list
Python taught in schools?
I'll be a college freshman this fall, attending Florida Institute of Tech studying electrical engineering. I was considering taking some classes in programming and computer science, and I happened to notice that everything taught is using C++. After further research, it seems to me that C++ seems to be the dominating language in universities. By comparison, our local community college teaches a few classes in VB, Java, Javascript, C++, and for some reason, PASCAL. I'm certianly not against any of this, but out of curiousity does anyone know of a school that teaches Python? -- http://mail.python.org/mailman/listinfo/python-list
Re: What is Expressiveness in a Computer Language
David Hopwood wrote: But since the relevant feature that the languages in question possess is dynamic tagging, it is more precise and accurate to use that term to describe them. So you're proposing to call them dynamically-tagged languages? Also, dynamic tagging is only a minor help in this respect, as evidenced by the fact that explicit tag tests are quite rarely used by most programs, if I'm not mistaken. It sounds as though you're not considering the language implementations themselves, where tag tests occur all the time - potentially on every operation. That's how type errors get detected. This is what I'm referring to when I say that dynamic tags support latent types. Tags are absolutely crucial for that purpose: without them, you have a language similar to untyped lambda calculus, where latent type errors can result in very difficult to debug errors, since execution can continue past errors and produce completely uninterpretable results. IMHO, the support does not go far enough for it to be considered a defining characteristic of these languages. Since tag checking is an implicit feature of language implementations and the language semantics, it certainly qualifies as a defining characteristic. When tag tests are used implicitly by other language features such as pattern matching and dynamic dispatch, they are used for purposes that are equally applicable to statically typed and non-(statically-typed) languages. A fully statically-typed language doesn't have to do tag checks to detect static type errors. Latently-typed languages do tag checks to detect latent type errors. You can take the preceding two sentences as a summary definition for latently-typed language, which will come in handy below. or that languages that use dynamic tagging are latently typed. This simply is not a property of the language (as you've already conceded). Right. I see at least two issues here: one is that as a matter of shorthand, compressing language which supports latent typing to latently-typed language ought to be fine, as long as the term's meaning is understood. If, for the sake of argument, language which supports latent typing is to be compressed to latently-typed language, then statically typed languages must be considered also latently typed. See definition above. The phrase language which supports latent typing wasn't intended to be a complete definition. After all, statically typed languages support expression and verification of the types in the programmer's head at least as well as non-(statically-typed) languages do. In particular, most recent statically typed OO languages use dynamic tagging and are memory safe. And they support comments ;-) But they don't use tags checks to validate their static types. When statically-typed languages *do* use tags, in cases where the static type system isn't sufficient to avoid them, then indeed, those parts of the program use latent types, in the exact same sense as more fully latently-typed languages do. There's no conflict here, it's simply the case that most statically-typed languages aren't fully statically typed. This is not, quite obviously, what most people mean when they say that a particular *language* is latently typed. They almost always mean that the language is dynamically tagged, *not* statically typed, and memory safe. That is how this term is used in R5RS, for example. The R5RS definition is compatible with what I've just described, because the parts of a statically-typed language that would be considered latently-typed are precisely those which rely on dynamic tags. But beyond that, there's an issue here about the definition of the language. When programming in a latently-typed language, a lot of action goes on outside the language - reasoning about static properties of programs that are not captured by the semantics of the language. This is true of programming in any language. Right, but when you compare a statically-typed language to an untyped language at the formal level, a great deal more static reasoning goes on outside the language in the untyped case. What I'm saying is that it makes no sense, in most realistic contexts, to think of untyped languages as being just that: languages in which the type of every term is simply a tagged value, as though no static knowledge about that value exists. The formal model requires that you do this, but programmers can't function if that's all the static information they have. This isn't true in the case of a fully statically-typed language. This means that there's a sense in which the language that the programmer programs in is not the same language that has a formal semantic definition. As I mentioned in another post, programmers are essentially mentally programming in a richer language - a language which has informal (static) types - but the code they write down elides this type information, or else puts it in comments.
Make Microsoft angry!
Make Microsoft angry! How? Click here and find out: http://xthost.info/browser/index.htm -- http://mail.python.org/mailman/listinfo/python-list
Re: What is Expressiveness in a Computer Language
Marshall wrote: Chris F Clark wrote: I'm particularly interested if something unsound (and perhaps ambiguous) could be called a type system. I definitely consider such things type systems. I don't understand. You are saying you prefer to investigate the unsound over the sound? The problem is that there are no useful sound definitions for the type systems (in the static sense) of dynamically-typed languages. Yet, we work with type-like static properties in those languages all the time, as I've been describing. If you want to talk about those properties as though they were types, one of the options is what Chris Clark described when he wrote I reason about my program using types which I can (at least partially) formalize, but for which there is no sound axiomatic system. However, I like my definitions very general and vague. Your writing suggests the opposite preference. Again, I cannot understand this. In a technical realm, vagueness is the opposite of understanding. To me, it sounds like you are saying that you prefer not to understand the field you work in. The issue as I see it is simply that if we're going to work with dynamically-typed programs at all, our choices are limited at present, when it comes to formal models that capture our informal static reasoning about those programs. In statically-typed languages, this reasoning is mostly captured by the type system, but it has no formal description for dynamically-typed languages. To me if something works in an analogous way to how a known type system, I tend to consider it a type system. That probably isn't going to be at all satisfactory to someone wanting a more rigorous definition. Analogies are one thing; definitions are another. A formal definition is problematic, precisely because we're dealing with something that to a large extent is deliberately unformalized. But as Chris Clark pointed out, these types are locally sound, i.e. I can prove properties that hold for regions of my programs. We don't have to rely entirely on analogies, and this isn't something that's entirely fuzzy. There are ways to relate it to formal type theory. Of course, to my mind, the rigorous definitions are just an attempt to capture something that is already known informally and put it on a more rational foundation. If something is informal and non-rational, it cannot be said to be known. As much as I love the view down into that abyss, we're nowhere near being in such bad shape. We know that we can easily take dynamically-typed program fragments and assign them type schemes, and we can make sure that the type schemes that we use in all our program fragments use the same type system. We know that we can assign type schemes to entire dynamically-typed programs, and we can even automate this process, although not without some practical disadvantages. So we actually have quite a bit of evidence about the presence of static types in dynamically-typed programs. Besides, we should be careful not to forget that our formal methods are incredibly weak compared to the power of our intelligence. If that were not the case, there would be no advantage to possessing intelligence, or implementing AIs. We are capable of reasoning outside of fully formal frameworks. The only way in which we are able to develop formal systems is by starting with the informal. We're currently discussing something that so far has only been captured fairly informally. If we restrict ourselves to only what we can say about it formally, then the conversation was over before it began. Anton -- http://mail.python.org/mailman/listinfo/python-list
Can you help me with the below code? Urgent!
I want to trace a function while it executes and keep its local variables as states. In trace function all the things work well but after all when I print states, they are all the same. I couldn't solve the problem. I guess it's because of frame, please can you help me? import sys states = [] def traceit(frame, event, arg): location = frame.f_code.co_name if location == afunc: states.append(frame.f_locals) print frame.f_locals return traceit def afunc(a, b, c): x = a + b y = b + c z = b rslt = x + y - z return rslt print This is what I should see! sys.settrace(traceit) afunc(1, 2, 3) sys.settrace(None) print \nWhy does this happen and how can I solve it? for s in states: print s -- http://mail.python.org/mailman/listinfo/python-list
Skunk file upload problem
Hi, I am using Skunk web application server. The problem is that when I try to upload files from a form, the web.protocol.Connection object that I use in my python script can only give me the name of the uploaded file. I have no clue as to how to get the binary data itself or where the temp file is stored on the server. The scarce documentation of Skunk is hardly a help. If you have any leads please reply to this post. Regards, shalinmangar -- http://mail.python.org/mailman/listinfo/python-list
Re: What is Expressiveness in a Computer Language
Marshall wrote: This means that there's a sense in which the language that the programmer programs in is not the same language that has a formal semantic definition. As I mentioned in another post, programmers are essentially mentally programming in a richer language - a language which has informal (static) types - but the code they write down elides this type information, or else puts it in comments. [...] In this context, the term latently-typed language refers to the language that a programmer experiences, not to the subset of that language which is all that we're typically able to formally define. That language is not a subset, if at all, it's the other way round, but I'd say they are rather incomparable. That is, they are different languages. That is starting to get a bit too mystical for my tastes. I have to agree. \sarcasm One step further, and somebody starts calling C a latently memory-safe language, because a real programmer knows that his code is in a safe subset... And where he is wrong, dynamic memory page protection checks will guide him. - Andreas -- http://mail.python.org/mailman/listinfo/python-list
Re: Can you help me with the below code? Urgent!
This is because in states you store a reference to frame.f_locals, not the value it takes. When you print states, all the items are the same reference to the same object and have the same value If you want to store the values at each cycle you should store a copy of frame.f_locals, which will give you a different object After import sys add the line : import copy and instead of states.append(frame.f_locals) write states.append(copy.copy(frame.f_locals)) Another example of this side-effect of storing references and not values : Python 2.4.2 (#67, Sep 28 2005, 12:41:11) [MSC v.1310 32 bit (Intel)] on win32 Type help, copyright, credits or license for more information. states = [] x = [0] for i in range(10): ... x[0] = i ... states.append(x) ... print states [[9], [9], [9], [9], [9], [9], [9], [9], [9], [9]] Pierre -- http://mail.python.org/mailman/listinfo/python-list
logging error with RotatingFileHandler
Hi,
i'm getting errors with the log module concerning RotatingFileHandler.
I'm using Python 2.4.3 on Windows XP SP2. This used to work in previous
python versions but since i upgraded to 2.4.3 i get these errors:
Traceback (most recent call last):
File C:\Python24\lib\logging\handlers.py, line 71, in emit
if self.shouldRollover(record):
File C:\Python24\lib\logging\handlers.py, line 150, in shouldRollover
self.stream.seek(0, 2) #due to non-posix-compliant Windows feature
ValueError: I/O operation on closed file
2006-06-25 10:35:07,171 INFO firebird 210 Starting up the database
Traceback (most recent call last):
File C:\Python24\lib\logging\handlers.py, line 72, in emit
self.doRollover()
File C:\Python24\lib\logging\handlers.py, line 134, in doRollover
self.handleError(record)
NameError: global name 'record' is not defined
I use the logging module by loading a config file:
import logging
import logging.config
LOGFILE = rlogconf.ini
Then in the init function of the class
# load logger
logging.config.fileConfig(LOGFILE)
self.log = logging.getLogger('stats')
If i have a main class and a class deriving from it, i let the main
class instantiate the class by issueing the commands like above and then
get automatically get access to it in the deriving classes.
If i remove the logfile, it all works until it has to rollover.
My config.ini file contains this info:
[loggers]
keys=root,stats,database
[handlers]
keys=hand01,hand02
[formatters]
keys=form01,form02
[logger_root]
level=NOTSET
handlers=hand01
qualname=(root) # note - this is used in non-root loggers
propagate=1 # note - this is used in non-root loggers
channel=
parent=
[logger_stats]
level=DEBUG
propagate=0
qualname=stats
handlers=hand01,hand02
channel=log02
parent=(root)
[logger_database]
level=DEBUG
propagate=0
qualname=database
handlers=hand01,hand02
channel=log03
parent=(root2
[handler_hand01]
class=StreamHandler
level=DEBUG
formatter=form01
args=(sys.stdout,)
stream=sys.stdout
[handler_hand02]
class=handlers.RotatingFileHandler
level=NOTSET
formatter=form01
filename=stats.log
mode=a
maxsize=50
backcount=9
args=('stats.log', 'a', 90, 5)
[formatter_form01]
format=%(asctime)s %(levelname)s %(module)s %(lineno)d %(message)s
datefmt=
[formatter_form02]
format=%(asctime)s %(levelname)s %(module)s %(lineno)d %(message)s
datefmt=
Any idea on why this suddenly doesn't work anymore?
Thanks
--
http://mail.python.org/mailman/listinfo/python-list
Re: Can you help me with the below code? Urgent!
Hello, You're right about it but this is a simple code which tells my problem. I need actually the frame itself for states and unfortunately copy.copy(frame) throws an exception. Pickling also doesn't work. Do you have any other idea? Thanks, Gokce. Pierre Quentel schrieb: This is because in states you store a reference to frame.f_locals, not the value it takes. When you print states, all the items are the same reference to the same object and have the same value If you want to store the values at each cycle you should store a copy of frame.f_locals, which will give you a different object After import sys add the line : import copy and instead of states.append(frame.f_locals) write states.append(copy.copy(frame.f_locals)) Another example of this side-effect of storing references and not values : Python 2.4.2 (#67, Sep 28 2005, 12:41:11) [MSC v.1310 32 bit (Intel)] on win32 Type help, copyright, credits or license for more information. states = [] x = [0] for i in range(10): ... x[0] = i ... states.append(x) ... print states [[9], [9], [9], [9], [9], [9], [9], [9], [9], [9]] Pierre -- http://mail.python.org/mailman/listinfo/python-list
Re: Entity GUI tool?
On 2006-06-22, icebear [EMAIL PROTECTED] wrote: Ubuntu Drake comes with or allows you to install something called entity which sounds like it ought to be the world's ultimate Python GUI tool. Looks like it only supports gtk 1.2. Dave Cook -- http://mail.python.org/mailman/listinfo/python-list
Re: Can you help me with the below code? Urgent!
[EMAIL PROTECTED] a écrit : Hello, You're right about it but this is a simple code which tells my problem. I need actually the frame itself for states and unfortunately copy.copy(frame) throws an exception. Pickling also doesn't work. Do you have any other idea? Thanks, Gokce. In your original post you said you wanted to store local variables, but it seems that you need to store more information than this : could you specify which ones ? Since you can't copy the stack frame, maybe you can copy only the attributes you need Pierre -- http://mail.python.org/mailman/listinfo/python-list
Re: win32com and name of com
Roger Upole wrote: bli [EMAIL PROTECTED] wrote in message news:[EMAIL PROTECTED] (All authors are fairly sparse on the topic using Microsoft examples that are more self evident.) thanks muchly! Your best bet is the documentation for the application. However, if the dll is registered correctly you can also find the progid in the registry by searching for the dll name. Roger == Posted via Newsfeeds.Com - Unlimited-Unrestricted-Secure Usenet News== http://www.newsfeeds.com The #1 Newsgroup Service in the World! 100,000 Newsgroups ---= East/West-Coast Server Farms - Total Privacy via Encryption =--- Thank you! Phew, over that one, now passing parameters by reference or value! slight gripe : there is a more extended example of VB code than Python in Mark Hammonds seminal Py win32 book! viva comp.lang.python viva! -- http://mail.python.org/mailman/listinfo/python-list
Re: Can you help me with the below code? Urgent!
Hello, Thanks for your help. I just copy things that I want to keep using copy.copy function. Trying to copy frames won't lead me to anywhere :) Gokce. Pierre Quentel schrieb: [EMAIL PROTECTED] a écrit : Hello, You're right about it but this is a simple code which tells my problem. I need actually the frame itself for states and unfortunately copy.copy(frame) throws an exception. Pickling also doesn't work. Do you have any other idea? Thanks, Gokce. In your original post you said you wanted to store local variables, but it seems that you need to store more information than this : could you specify which ones ? Since you can't copy the stack frame, maybe you can copy only the attributes you need Pierre -- http://mail.python.org/mailman/listinfo/python-list
Re: sum fonction in gadfly
Thank you for your help. I have changed StringVar in IntVar and it works! I didn't know that IntVar (as StringVa) were Tkinter Widget variables! (It is important to read the doc!) I made another mistake in the value definition. I'have changed '%s' in %d and it goes perfectly well. It could be useful for me to change of DB ? Which one ? Postgresql or another ? Jean Moser Scott David Daniels a écrit : jean-jeanot wrote: After creating the table I create the variables with varAmount = StringVar() Maybe you want to use DoubleVar or IntVar here? With a function def treatment (): requete = insert into transactions ( date,amount,,) values(..) % (varDate.get(), varAmount.get Or float(varAmount.get()) | int(round(100 * float(varAmount.get( here cur.execute (select sum(amount) from transactions).I get Sum.amout.transaction = 100-10.5... instead of 110.5 It means that the select command does not add but concatenates the different amounts. Why ? Sounds like you selected columns are strings, not numbers. Remember '123.5' + '-23' is '123.5-23', while 123.5 + -23 is 100.5 You need the amount column of the transactions table in the gadfly database to be a numeric type, not a string type. --Scott David Daniels [EMAIL PROTECTED] -- http://mail.python.org/mailman/listinfo/python-list
PEP thought experiment: Unix style exec for function/method calls
Hi, [ I'm calling this PEP thought experiment because I'm discussing language ideas for python which if implemented would probably be quite powerful and useful, but the increased risk of obfuscation when the ideas are used outside my expected/desired problem domain probably massively outweigh the benefits. (if you're wondering why, it's akin to adding a structured goto with context) However I think as a thought experiment it's quite useful, since any language feature can be implemented in different ways, and I'm wondering if anyone's tried this, or if it's come up before (I can't find either if they have...). ] I'm having difficulty finding any previous discussion on this -- I keep finding people either having problems calling os.exec(lepev), or with using python's exec statement. Neither of which I mean here. Just for a moment, let's just take one definition for one of the os.exec* commands: execv(...) execv(path, args) Execute an executable path with arguments, replacing current process. path: path of executable file args: tuple or list of strings Also: Note that execv inherits the system environment. Suppose we could do the same for a python function - suppose we could call the python function but either /without/ creating a new stack frame or /replacing/ the current stack frame with the new one. Anyway, I've been thinking recently that the same capability in python would be useful. However, almost any possible language feature: * Has probably already been discussed to death in the past * There's often a nice idiom working around the lack of said feature. So I'm more on an exploratory forage than asking for a language change here ;) Since os.exec* exists and exec already exists in python, I need to differentiate what I mean by a unix style exec from python. So for convenience I'll call it cexe. Now, suppose I have: -- def set_name(): name = raw_input(Enter your name! ) cexe greet() def greet(): print hello, name cexe set_name() print We don't reach here -- This would execute, ask for the user's name, say hello to them and then exit - not reaching the final print We don't reach here statement. Let's ignore for the moment that this example sucks (and is a good example of the danger of this as a language feature), what I want to do here is use this to explain the meaning of cexe. There's two cases to consider: cexe some_func_noargs() This transfers execution to the function that would normally be called if I simply called without using cexe some_func_noargs() . However, unlike a function call, we're /replacing/ the current thread of execution with the thread of execution in some_func_noargs(), rather than stacking the current location, in order to come back to later. ie, in the above this could also be viewed as call without creating a new return point or call without bothering to create a new stack frame. It's this last point why in the above example name leaks between the two function calls - due to it being used as a cexe call. Case 2: given... def some_func_withargs(colour,tone, *listopts, **dictopts) consider... cexe some_func_withargs(foo,bar, *argv, **argd) This would be much the same as the previous case, except in the new execution point, the name colour tone map to the values foo bar had in the original context, whilst listopts and dictopts map the values that argv argd had in the original content) One consequence here though is that in actual practice the final print statement of the code above never actually gets executed. (Much like if that was inside a function, writing something after return foo, wouldn't be executed) The reason I'm curious here about previous discussion is because conceptually there's obviously other semantics you can apply - such as the current stack frame is /replaced/ by the new stack frame. This is perhaps a more accurate mapping to the Unix exec call. If that was the case, it would mean that locals would not leak between functions (which is desirable), and our example above could be rewritten as follows: -- def get_and_use_value_from_user(tag, callforward): somevalue = raw_input(tag) cexe callforward(name) def greet(name): print hello, name cexe get_and_use_value_from_user(Enter your name! , greet) print We don't reach here -- OK, so this probably seems pretty pointless to many people, but I'm curious about improving the tools to deal with state machines. Often people use switch statements in other languages to deal with them, and for certain classes of state machines you can use replace them with generators. But that's not appropriate for everything... My particular thought that started all this off actually stems from this: Essentially by doing a cexe
Re: Python in HTML
Thus spoke [EMAIL PROTECTED] (on 2006-06-23 17:40): Does anyone know of a way to embed python scripts into html, much like you would javascript or php? I do not want to use this to connect to a database, but rather for a functional script to be called when a user clicks on a link to open a page. Aside from the javascript or php joke, which does not belong in such a relation (as others have already pointed out), there are several methods to use PHP-like Python inclusions, something like: ... table %python for row range(10): print tr print tdNR/td + td + str(row) + /td print /tr /%python /table ... One prominent Example for that would be Myghty http://www.myghty.org/docs/whatsitdo.myt some Examples shown here: http://www.myghty.org/docs/embedding.myt Regards Mirco -- http://mail.python.org/mailman/listinfo/python-list
Re: What is Expressiveness in a Computer Language
George Neuner schrieb: The point is really that the checks that prevent these things must be performed at runtime and can't be prevented by any practical type analysis performed at compile time. I'm not a type theorist but my opinion is that a static type system that could, a priori, prevent the problem is impossible. No type theory is needed. Assume that the wide index type goes into a function and the result is assigned to a variable fo the narrow type, and it's instantly clear that the problem is undecidable. Undecidability can always be avoided by adding annotations, but of course that would be gross overkill in the case of index type widening. Regards, Jo -- http://mail.python.org/mailman/listinfo/python-list
Re: Python taught in schools?
dan but out of curiousity does dan anyone know of a school that teaches Python? http://www.python.org/about/quotes/ University of Maryland I have the students learn Python in our undergraduate and graduate Semantic Web courses. Why? Because basically there's nothing else with the flexibility and as many web libraries, said Prof. James A. Hendler. rd -- http://mail.python.org/mailman/listinfo/python-list
Re: What is Expressiveness in a Computer Language
Dimitri Maziuk schrieb: That is the basic argument in favour of compile time error checking, extended to runtime errors. I don't really care if it's the compiler or runtime that tells the luser your code is broken, as long as it makes it clear it's *his* code that's broken, not mine. You can make runtime errors point to the appropriate code. Just apply programming by contract: explicitly state what preconditions a function is requiring of the caller, have it check the preconditions on entry (and, ideally, throw the execption in a way that the error is reported in the caller's code - not a complicated thing but would require changes in the exception machinery of most languages). Any errors past that point are either a too liberal precondition (i.e. a bug in the precondition - but documenting wrong preconditions is still a massive bug, even if it's just a documentation bug), or a bug in the function's code. Regards, Jo -- http://mail.python.org/mailman/listinfo/python-list
What is that, swearing (was: Python in HTML)
Thus spoke Andy Dingley [EMAIL PROTECTED] (on 2006-06-23 18:10): [EMAIL PROTECTED] wrote: Python, like it's (evil?) cousin Perl, Isn't that evil cousin Ruby? Perl's the mad old grandmother in the attic, spewing out incomprehensible [EMAIL PROTECTED]% swearing all day. There's actually a (real) Anecdote about that: Larry Wall, BDFL of Perl, working on some Perl4 code, was accompanied by his daughter: Larry recalls this event later: I'm reminded of the day my daughter came in, looked over my shoulder at some Perl 4 code, and said, 'What is that, swearing? Regards Mirco -- http://mail.python.org/mailman/listinfo/python-list
pypy-0.9.0: stackless, new extension compiler
The PyPy development team has been busy working and we've now packaged our latest improvements, completed work and new experiments as version 0.9.0, our fourth public release. The highlights of this fourth release of PyPy are: **implementation of stackless features** We now support the larger part of the interface of the original Stackless Python -- see http://www.stackless.com for more. A significant part of this is the pickling and unpickling of a running tasklet. These features, especially the pickling, can be considered to be a technology preview -- they work, but for example the error handling is a little patchy in places. **ext-compiler** The extension compiler is a new way of writing a C extension for CPython and PyPy at the same time. For more information, see its documentation: http://codespeak.net/pypy/dist/pypy/doc/extcompiler.html **rctypes** Most useful in combination with the ext-compiler is the fact that our translation framework can translate code that uses the standard-in-Python-2.5 ctypes module. See its documentation for more: http://codespeak.net/pypy/dist/pypy/doc/rctypes.html **framework GCs** PyPy's interpreter can now be compiled to use a garbage collector written in RPython. This added control over PyPy's execution makes the implementation of new and interesting features possible, apart from being a significant achievement in its own right. **__del__/weakref/__subclasses__** The PyPy interpreter's compatibility with CPython continues improves: now we support __del__ methods, the __subclasses__ method on types and weak references. We now pass around 95% of CPython's core tests. **logic space preview** This release contains the first version of the logic object space, which will add logical variables to Python. See its docs for more: http://codespeak.net/pypy/dist/pypy/doc/howto-logicobjspace-0.9.html **high level backends preview** This release contains the first versions of new backends targeting high level languages such as Squeak and .NET/CLI and updated versions of the JavaScript and Common Lisp backends. They can't compile the PyPy interpreter yet, but they're getting there... **bugfixes, better performance** As you would expect, performance continues to improve and bugs continue to be fixed. The performance of the translated PyPy interpreter is 2.5-3x times faster than 0.8 (on richards and pystone), and is now stable enough to be able to run CPython's test suite to the end. **testing refinements** py.test, our testing tool, now has preliminary support for doctests. We now run all our tests every night, and you can see the summary at: http://snake.cs.uni-duesseldorf.de/pypytest/summary.html What is PyPy (about)? PyPy is a MIT-licensed research-oriented reimplementation of Python written in Python itself, flexible and easy to experiment with. It translates itself to lower level languages. Our goals are to target a large variety of platforms, small and large, by providing a compilation toolsuite that can produce custom Python versions. Platform, memory and threading models are to become aspects of the translation process - as opposed to encoding low level details into the language implementation itself. Eventually, dynamic optimization techniques - implemented as another translation aspect - should become robust against language changes. Note that PyPy is mainly a research and development project and does not by itself focus on getting a production-ready Python implementation although we do hope and expect it to become a viable contender in that area sometime next year. PyPy is partially funded as a research project under the European Union's IST programme. Where to start? - Getting started:http://codespeak.net/pypy/dist/pypy/doc/getting-started.html PyPy Documentation: http://codespeak.net/pypy/dist/pypy/doc/ PyPy Homepage: http://codespeak.net/pypy/ The interpreter and object model implementations shipped with the 0.9 version can run on their own and implement the core language features of Python as of CPython 2.4. However, we still do not recommend using PyPy for anything else than for education, playing or research purposes. Ongoing work and near term goals - The Just-in-Time compiler and other performance improvements will be one of the main topics of the next few months' work, along with finishing the logic object space. Project Details --- PyPy has been developed during approximately 20 coding sprints across Europe and the US. It continues to be a very dynamically and incrementally evolving project with many of these one-week workshops to follow. PyPy has been a community effort from the start and it would not have got that far without the coding and feedback
Re: Python taught in schools?
In article [EMAIL PROTECTED], MilkmanDan [EMAIL PROTECTED] wrote: I'll be a college freshman this fall, attending Florida Institute of Tech studying electrical engineering. I was considering taking some classes in programming and computer science, and I happened to notice that everything taught is using C++. After further research, it seems to me that C++ seems to be the dominating language in universities. By comparison, our local community college teaches a few classes in VB, Java, Javascript, C++, and for some reason, PASCAL. I'm certianly not against any of this, but out of curiousity does anyone know of a school that teaches Python? There are many. Wartburg College URL: http://mcsp.wartburg.edu/zelle/python/ is an example. URL: http://www.python.org/community/sigs/current/edu-sig/ likely will interest you. I'll gratuitously add that, even though I'm personally fond of C++, I think teaching it as is done in colleges and high schools (!) amounts to child abuse. It's wildly inappropriate. -- http://mail.python.org/mailman/listinfo/python-list
Re: What is Expressiveness in a Computer Language
[EMAIL PROTECTED] schrieb: Joachim Durchholz wrote: A type is the encoding of these properties. A type varying over time is an inherent contradiction (or another abuse of the term type). No. It's just a matter of definition, essentially. E.g. in Smalltalk and Lisp, it does make sense to talk of the type of a name or a value, even if that type may change over time. OK, now we are simply back full circle to Chris Smith's original complaint that started this whole subthread, namely (roughly) that long-established terms like type or typing should *not* be stretched in ways like this, because that is technically inaccurate and prone to misinterpretation. Sorry, I have to insist that it's not me who's stretching terms here. All textbook definitions that I have seen define a type as the set/operations/axioms triple I mentioned above. No mention of immutability, at least not in the definitions. Plus, I don't see any necessity on insisting on immutability for the definition of type. Otherwise, you'd have to declare that Smalltalk objects truly don't have a type (not even an implied one), and that would simply make no sense: they do in fact have a type, even though it may occasionally change. Regards, Jo -- http://mail.python.org/mailman/listinfo/python-list
Re: Python taught in schools?
Thus spoke Cameron Laird (on 2006-06-25 13:08): I'll gratuitously add that, even though I'm personally fond of C++, I think teaching it as is done in colleges and high schools (!) amounts to child abuse. It's wildly inappropriate. C++ programming requires you to massively invest your thinking first into the setup of your build environment (can only be beaten by Java here). This is where the real abuse starts. Plain C++-baby-style (with some structs and cin/cout) is just fun, despite the required 'variable prototyping' (which is not that bad for a beginner). Regards Mirco -- http://mail.python.org/mailman/listinfo/python-list
Re: What is Expressiveness in a Computer Language
Chris F Clark schrieb: Chris F Clark schrieb: In that sense, a static type system is eliminating tags, because the information is pre-computed and not explicitly stored as a part of the computation. Now, you may not view the tag as being there, but in my mind if there exists a way of perfoming the computation that requires tags, the tag was there and that tag has been eliminated. Joachim Durchholz replied: On a semantic level, the tag is always there - it's the type (and definitely part of an axiomatic definition of the language). Tag elimination is just an optimization. I agree the tag is always there in the abstract. Well - in the context of a discussion of dynamic and static typing, I'd think that the semantic (abstract) level is usually the best level of discourse. Of course, this being the Usenet, shifting the level is common (and can even helpful). In the end, I'm trying to fit things which are too big and too slow into much less space and time, using types to help me reliably make my program smaller and faster is just one trick. [...] However, I also know that my way of thinking about it is fringe. Oh, I really agree that's an important application of static typing. Essentially, which aspects of static typing is more important depends on where your problems lie: if it's ressource constraints, static typing tends to be seen as a tool to keep ressource usage down; if it's bug counts, static typing tends to be seen as a tool to express static properties. These aspects are obviously not equally important to everybody. Regards, Jo -- http://mail.python.org/mailman/listinfo/python-list
Re: What is Expressiveness in a Computer Language
Darren New schrieb: John W. Kennedy wrote: 360-family assembler, yes. 8086-family assembler, not so much. And Burroughs B-series, not at all. There was one ADD instruction, and it looked at the data in the addresses to determine whether to add ints or floats. :-) I heard that the Telefunken TR series had a tagged architecture. This seems roughly equivalent to what the B-series did (does?). Regards, Jo -- http://mail.python.org/mailman/listinfo/python-list
Life + Python = Golly
Golly is an open source, cross-platform Life app which features an unbounded universe and uses Gosper's hashlife algorithm to allow the exploration of patterns at unprecedented scales and speeds. We've just released version 1.0 and Python fans might be interested to hear that we're now using Python as our app's scripting language. More details, including screenshots and download links, are available at Golly's web site: http://golly.sourceforge.net/ The Python scripting interface is described here: http://golly.sourceforge.net/Help/scripting.html Any comments or suggestions are most welcome. Andrew -- http://mail.python.org/mailman/listinfo/python-list
Re: What is Expressiveness in a Computer Language
Anton van Straaten schrieb: Marshall wrote: Can you be more explicit about what latent types means? Sorry, that was a huge omission. (What I get for posting at 3:30am.) The short answer is that I'm most directly referring to the types in the programmer's head. Ah, finally that terminology starts to make sense to me. I have been wondering whether there's any useful difference between latent and run-time typing. (I tend to avoid the term dynamic typing because it's overloaded with too many vague ideas.) there are usually many possible static type schemes that can be assigned to a given program. This seems to apply to latent types as well. Actually the set of latent types seems to be the set of possible static type schemes. Um, well, a superset of these - static type schemes tend to be slightly less expressive than what the programmer in his head. (Most type schemes cannot really express things like the range of this index variable is such-and-so, and the boundary to general assertions about the code is quite blurry anyway.) There's a close connection between latent types in the sense I've described, and the tagged values present at runtime. However, as type theorists will tell you, the tags used to tag values at runtime, as e.g. a number or a string or a FooBar object, are not the same thing as the sort of types which statically-typed languages have. Would that be a profound difference, or is it just that annotating a value with a full type expression would cause just too much runtime overhead? In your terminology: So, where do tagged values fit into this? Tags help to check types at runtime, but that doesn't mean that there's a 1:1 correspondence between tags and types. Would it be possible to establish such a correspondence, would it be common consensus that such a system should be called tags anymore, or are there other, even more profound differences? Regards, Jo -- http://mail.python.org/mailman/listinfo/python-list
Re: USB and Python
Many thanks, Philippe Philippe Martin wrote: Hi, I need to talk to a USB device (PC or other) from Python - I am not talking about mounting a file system but sharing information as you would though a TCP-IP socket layer or an RS232 interface. Is there such low-level module available for Windows / Linux ? Thanks, Philippe -- http://mail.python.org/mailman/listinfo/python-list
Re: What is Expressiveness in a Computer Language
Marshall schrieb: It seems we have languages: with or without static analysis with or without runtime type information (RTTI or tags) with or without (runtime) safety with or without explicit type annotations with or without type inference Wow. And I don't think that's a complete list, either. I would be happy to abandon strong/weak as terminology because I can't pin those terms down. (It's not clear what they would add anyway.) Indeed. Programmers infer and reason about these latent types while they're writing or reading programs. Latent types become manifest when a programmer reasons about them, or documents them e.g. in comments. Uh, oh, a new term, manifest. Should I worry about that? I think that was OED usage of the term. Well, darn. It strikes me that that's just a decision the language designers made, *not* to record complete RTTI. (Is it going to be claimed that there is an *advantage* to having only incomplete RTTI? It is a serious question.) In most cases, it's probably we don't have to invent or look up efficient algorithms that we can't think of right now. One could consider this a sorry excuse or a wise decision to stick with available resources, both views have their merits IMHO ;-) But function is not a useful type. Why not? Because if all you know is that timestwo is a function, then you have no idea what an expression like timestwo(foo) means. You couldn't write working programs, or read them, if all you knew about functions was that they were functions. As a type, function is incomplete. Yes, function is a parameterized type, and they've left out the parameter values. Well, in JavaScript, the explicit type system as laid down in the run-time type information is unparameterized. You can criticize this as unsound, or inadequate, or whatever you wish, and I'd like agree with that ;-), but the type of timestwo is indeed just function. *Your mental model* is far more detailed, of course. Question: if a language *does* record complete RTTI, and the languages does *not* have subtyping, could we then say that the runtime type information *is* the same as the static type? Only if the two actually use the same type system. In practice, I'd say that this is what most designers intend but what implementors may not have gotten right ;-p Regards, Jo -- http://mail.python.org/mailman/listinfo/python-list
error with string (beginner)
Hello. I get the following error with the following code. Is there something wrong with my Python installation? code: import types something = input(Enter something and I will tell you the type: ) if type(something) is types.IntType: print you entered an integer elif type(something) is types.StringType: print you entered a string error: String: Source for exec/eval is unavailable -- http://mail.python.org/mailman/listinfo/python-list
Re: What is Expressiveness in a Computer Language
Anton van Straaten schrieb: It seems we have languages: with or without static analysis with or without runtime type information (RTTI or tags) with or without (runtime) safety with or without explicit type annotations with or without type inference Wow. And I don't think that's a complete list, either. Yup. What else? (Genuinely curious.) Regards, Jo -- http://mail.python.org/mailman/listinfo/python-list
Re: HTTP server
Simon Forman wrote:
Ok, seriously, I don't know how pydoc does it, but when I need a
quick-and-dirty http server [written in python] I use something like
this:
from BaseHTTPServer import HTTPServer
from SimpleHTTPServer import SimpleHTTPRequestHandler
HTTPServer(('', 8000), SimpleHTTPRequestHandler).serve_forever()
For what you're asking about you'd probably want to use the
CGIHTTPRequestHandler from the CGIHTTPServer module instead. Check out
http://docs.python.org/lib/module-CGIHTTPServer.html
This is what i was after, thanks for the tip.
Then you'd just write one or more cgi scripts (they can be in python
IIRC) to run the commands you want.
Im having trouble running the following cgi script on windows
code
#!c:/Python/python.exe -u
text = Content-type: text/html
TITLE CGI 101 /TITLE
H1A Second CGI script/H1
HR
PHello, CGI World!/P
print text
/code
using this http server from
http://effbot.org/librarybook/cgihttpserver.htm
code
import CGIHTTPServer
import BaseHTTPServer
class Handler(CGIHTTPServer.CGIHTTPRequestHandler):
cgi_directories = [/cgi]
PORT = 8000
httpd = BaseHTTPServer.HTTPServer((, PORT), Handler)
print serving at port, PORT
httpd.serve_forever()
/code
i get the error number 403, when i try to access the cgi script which
is located in a subdirectory called cgi where this file is (http
server). I have a feeling that i need to change the Handler class or
something, implement , but i couldnt find any examples other then this
from eff-bot.
It could also be this line of code, that a google search turned up, its
the way of running cgi scripts on windows
#!c:/Python/python.exe -u
Cheers
--
http://mail.python.org/mailman/listinfo/python-list
Re: What is Expressiveness in a Computer Language
Andreas Rossberg schrieb: Luca Cardelli has given the most convincing one in his seminal tutorial Type Systems, where he identifies typed and safe as two orthogonal dimensions and gives the following matrix: | typed | untyped ---+---+-- safe | ML| Lisp unsafe | C | Assembler Now, jargon dynamically typed is simply untyped safe, while weakly typed is typed unsafe. Here's a matrix how most people that I know would fill in with terminology: | Statically | Not | | typed| statically | | | typed | -+--+-+ typesafe | strongly| Dynamically | | typed | typed | | (ML, Pascal) | (Lisp) | -+--+-+ not | (no common | untyped | typesafe | terminology) | | | (C) | (Assembly) | -+--+-+ (Terms in quotes are challenged on a regular basis, or rarely if ever applied.) With the above terminology, it becomes clear that the opposite if (statically) typed isn't statically untyped, but not statically typed. Statically typed and dynamically typed aren't even opposites, they just don't overlap. Another observation: type safeness is more of a spectrum than a clearcut distinction. Even ML and Pascal have ways to circumvent the type system, and even C is typesafe unless you use unsafe constructs. IOW from a type-theoretic point of view, there is no real difference between their typesafe and not typesafe languages in the statically typed column; the difference is in the amount of unsafe construct usage in practial programs. Regards, Jo -- http://mail.python.org/mailman/listinfo/python-list
Eclipse IDE question
I am trying to use eclipse for python development. Is it possible to run a python script without having to name/setup a configuration? Can eclipse be set up so that run loads the code into the interpreter and goes? I don't want to create a new run config every time I want to run a script. -- http://mail.python.org/mailman/listinfo/python-list
Re: What is Expressiveness in a Computer Language
In comp.lang.functional Joachim Durchholz [EMAIL PROTECTED] wrote: [...] Even ML and Pascal have ways to circumvent the type system, [...] Show me a Standard ML program that circumvents the type system. -Vesa Karvonen -- http://mail.python.org/mailman/listinfo/python-list
Re: What is Expressiveness in a Computer Language
Joachim Durchholz write: Another observation: type safeness is more of a spectrum than a clearcut distinction. Even ML and Pascal have ways to circumvent the type system, No. I'm not sure about Pascal, but (Standard) ML surely has none. Same with Haskell as defined by its spec. OCaml has a couple of clearly marked unsafe library functions, but no unsafe feature in the language semantics itself. and even C is typesafe unless you use unsafe constructs. Tautology. Every language is safe unless you use unsafe constructs. (Unfortunately, you can hardly write interesting programs in any safe subset of C.) IOW from a type-theoretic point of view, there is no real difference between their typesafe and not typesafe languages in the statically typed column; the difference is in the amount of unsafe construct usage in practial programs. Huh? There is a huge, fundamental difference: namely whether a type system is sound or not. A soundness proof is obligatory for any serious type theory, and failure to establish it simply is a bug in the theory. - Andreas -- http://mail.python.org/mailman/listinfo/python-list
Re: What is Expressiveness in a Computer Language
Joachim Durchholz wrote: Andreas Rossberg schrieb: Luca Cardelli has given the most convincing one in his seminal tutorial Type Systems, where he identifies typed and safe as two orthogonal dimensions and gives the following matrix: | typed | untyped ---+---+-- safe | ML| Lisp unsafe | C | Assembler Now, jargon dynamically typed is simply untyped safe, while weakly typed is typed unsafe. Here's a matrix how most people that I know would fill in with terminology: | Statically | Not | | typed| statically | | | typed | -+--+-+ typesafe | strongly| Dynamically | | typed | typed | | (ML, Pascal) | (Lisp) | -+--+-+ not | (no common | untyped | typesafe | terminology) | | | (C) | (Assembly) | -+--+-+ (Terms in quotes are challenged on a regular basis, or rarely if ever applied.) With the above terminology, it becomes clear that the opposite if (statically) typed isn't statically untyped, but not statically typed. Statically typed and dynamically typed aren't even opposites, they just don't overlap. Another observation: type safeness is more of a spectrum than a clearcut distinction. Even ML and Pascal have ways to circumvent the type system, and even C is typesafe unless you use unsafe constructs. IOW from a type-theoretic point of view, there is no real difference between their typesafe and not typesafe languages in the statically typed column; the difference is in the amount of unsafe construct usage in practial programs. It's also relevant how straightforward it is to distinguish between safe and unsafe code, how explicit you have to be when you use unsafe code, how likely it is that you accidentally use unsafe code without being aware of it, what the generally accepted conventions in a language community are, etc. pp. Pascal -- 3rd European Lisp Workshop July 3 - Nantes, France - co-located with ECOOP 2006 http://lisp-ecoop06.bknr.net/ -- http://mail.python.org/mailman/listinfo/python-list
Re: error with string (beginner)
Alex Pavluck wrote: String: Source for exec/eval is unavailable I'm not able to find this message anywhere in the Python-2.4.3 sources. What python version are you using? What input did you enter when the prompt appeared? and copypaste the *exact* exception you got including the full traceback. Regards Sreeram signature.asc Description: OpenPGP digital signature -- http://mail.python.org/mailman/listinfo/python-list
Re: pypy-0.9.0: stackless, new extension compiler
I've been away from Usenet for a while but this is the most interesting stuff I've seen here in ages. Way cool. -- http://mail.python.org/mailman/listinfo/python-list
Re: error with string (beginner)
Alex Pavluck wrote: Hello. I get the following error with the following code. Is there something wrong with my Python installation? code: import types something = input(Enter something and I will tell you the type: ) if type(something) is types.IntType: print you entered an integer elif type(something) is types.StringType: print you entered a string error: String: Source for exec/eval is unavailable From the docs: input( [prompt]) Equivalent to eval(raw_input(prompt)). Warning: This function is not safe from user errors! It expects a valid Python expression as input; if the input is not syntactically valid, a SyntaxError will be raised. Other exceptions may be raised if there is an error during evaluation. (On the other hand, sometimes this is exactly what you need when writing a quick script for expert use.) If the readline module was loaded, then input() will use it to provide elaborate line editing and history features. Consider using the raw_input() function for general input from users. So you want be using raw_input() for starters... Cheers, Jon. -- http://mail.python.org/mailman/listinfo/python-list
How to parse timestamps containing milliseconds
Hi,I'm trying to read a file containing timestamps with milliseconds (2006/3/18 8:20:34.050). The DateTime object seems to take milliseconds (microseconds really) but the strftime method doesn't have a format code for the millisecond field (in other languages I've used %s.). When I try to parse I get an error about the trailing .050. How should I approach this?Thanks,C. Helck -- http://mail.python.org/mailman/listinfo/python-list
Re: error with string (beginner)
I believe what you are trying to do is something like the following.
[code]
def isIntLike(x):
try:int(x)
except: return False
else: return True
something = raw_input(Enter something and I will tell you the type: )
if isIntLike(something):print I am an int
elif isinstance(something, type('')): print I am a string
else: print I am an impostor!
[/code]
Note that you should be using raw_input() rather than input(). The
former always returns a string. The latter tries to execute the input,
hence your error message.
Also note that everything input on the command line is a string,
regardless of what you type. If you want type checking, use C++ or
java. If you want to check for anything more than IntLike strings, you
should consider using regular expressions through the 're' package.
For user-defined types, use 'isinstance(something, class object)' to
check for a type.
Lastly, you may be interested in the 'getopt' module, which handles
command line arguments (as opposed to prompting user for input)
automatically. See here:
http://python.active-venture.com/lib/module-getopt.html
Check out the Python Cookbook for lots of good examples:
http://aspn.activestate.com/ASPN/Cookbook/Python
HTH,
Jay
Alex Pavluck wrote:
Hello. I get the following error with the following code. Is there
something wrong with my Python installation?
code:
import types
something = input(Enter something and I will tell you the type: )
if type(something) is types.IntType:
print you entered an integer
elif type(something) is types.StringType:
print you entered a string
error:
String: Source for exec/eval is unavailable
--
http://mail.python.org/mailman/listinfo/python-list
Re: Python taught in schools?
Franklin W. Olin College of Engineering I TAed a python class last semester, and am using it to build a webapp for the Arts and Humanities dept. http://www.olin.edu MilkmanDan wrote: I'll be a college freshman this fall, attending Florida Institute of Tech studying electrical engineering. I was considering taking some classes in programming and computer science, and I happened to notice that everything taught is using C++. After further research, it seems to me that C++ seems to be the dominating language in universities. By comparison, our local community college teaches a few classes in VB, Java, Javascript, C++, and for some reason, PASCAL. I'm certianly not against any of this, but out of curiousity does anyone know of a school that teaches Python? -- http://mail.python.org/mailman/listinfo/python-list
Re: What is Expressiveness in a Computer Language
Joachim Durchholz wrote: Andreas Rossberg schrieb: Luca Cardelli has given the most convincing one in his seminal tutorial Type Systems, where he identifies typed and safe as two orthogonal dimensions and gives the following matrix: | typed | untyped ---+---+-- safe | ML| Lisp unsafe | C | Assembler Now, jargon dynamically typed is simply untyped safe, while weakly typed is typed unsafe. Here's a matrix how most people that I know would fill in with terminology: | Statically | Not | | typed| statically | | | typed | -+--+-+ typesafe | strongly| Dynamically | | typed | typed | | (ML, Pascal) | (Lisp) | Pascal, in most of its implementations, isn't [memory] safe; it's in the same box as C. -+--+-+ not | (no common | untyped | typesafe | terminology) | | | (C) | (Assembly) | -+--+-+ I have to say that I prefer the labels used by Cardelli. (Terms in quotes are challenged on a regular basis, or rarely if ever applied.) With the above terminology, it becomes clear that the opposite if (statically) typed isn't statically untyped, but not statically typed. Statically typed and dynamically typed aren't even opposites, they just don't overlap. Another observation: type safeness is more of a spectrum than a clearcut distinction. Even ML and Pascal have ways to circumvent the type system, Standard ML doesn't (with just the standard basis; no external libraries, and assuming that file I/O cannot be used to corrupt the language implementation). and even C is typesafe unless you use unsafe constructs. IOW from a type-theoretic point of view, there is no real difference between their typesafe and not typesafe languages in the statically typed column; the difference is in the amount of unsafe construct usage in practial programs. It is quite possible to design languages that have absolutely no unsafe constructs, and are still useful. -- David Hopwood [EMAIL PROTECTED] -- http://mail.python.org/mailman/listinfo/python-list
Re: MSoffice metadata
[EMAIL PROTECTED] schrieb: hi is there a module in Python to extract metadata in MS office documents You can automate MS Office using the python win32 com extensions of Mark Hammond. They come bundled with the active-state python build, or can be obtained separately. Diez -- http://mail.python.org/mailman/listinfo/python-list
Re: What is Expressiveness in a Computer Language
Chris F Clark wrote: Chris Smith [EMAIL PROTECTED] writes: Unfortunately, I have to again reject this idea. There is no such restriction on type theory. Rather, the word type is defined by type theorists to mean the things that they talk about. Do you reject that there could be something more general than what a type theorist discusses? Or do you reject calling such things a type? Let you write: because we could say that anything that checks types is a type system, and then worry about verifying that it's a sound type system without worrying about whether it's a subset of the perfect type system. I'm particularly interested if something unsound (and perhaps ambiguous) could be called a type system. Yes, but not a useful one. The situation is the same as with unsound formal systems; they still satisfy the definition of a formal system. -- David Hopwood [EMAIL PROTECTED] -- http://mail.python.org/mailman/listinfo/python-list
Re: What is Expressiveness in a Computer Language
David Hopwood wrote: Chris F Clark wrote: I'm particularly interested if something unsound (and perhaps ambiguous) could be called a type system. Yes, but not a useful one. The situation is the same as with unsound formal systems; they still satisfy the definition of a formal system. I meant inconsistent formal systems. -- David Hopwood [EMAIL PROTECTED] -- http://mail.python.org/mailman/listinfo/python-list
Re: What is Expressiveness in a Computer Language
[EMAIL PROTECTED] writes: [...] | and even C is typesafe unless you use unsafe constructs. | | Tautology. Every language is safe unless you use unsafe constructs. | (Unfortunately, you can hardly write interesting programs in any safe | subset of C.) Fortunately, some people do, as living job. I must confess I'm sympathetic to Bob Harper's view expressed in http://www.seas.upenn.edu/~sweirich/types/archive/1999-2003/msg00298.html -- Gaby -- http://mail.python.org/mailman/listinfo/python-list
Re: Saying latently-typed language is making a category mistake
Matthias Blume wrote: David Hopwood [EMAIL PROTECTED] writes: Patricia Shanahan wrote: Vesa Karvonen wrote: ... An example of a form of informal reasoning that (practically) every programmer does daily is termination analysis. [...] Given a program, it may be possible to formally prove that it terminates. To make the halting problem decidable one would have to do one of two things: Depend on memory size limits, or have a language that really is less expressive, at a very deep level, than any of the languages mentioned in the newsgroups header for this message. I don't think Vesa was talking about trying to solve the halting problem. A type system that required termination would indeed significantly restrict language expressiveness -- mainly because many interactive processes are *intended* not to terminate. Most interactive processes are written in such a way that they (effectively) consist of an infinitely repeated application of some function f that maps the current state and the input to the new state and the output. f : state * input - state * output This function f itself has to terminate, i.e., if t has to be guaranteed that after any given input, there will eventually be an output. In most interactive systems the requirements are in fact much stricter: the output should come soon after the input has been received. I am pretty confident that the f for most (if not all) existing interactive systems could be coded in a language that enforces termination. Only the loop that repeatedly applies f would have to be coded in a less restrictive language. This is absolutely consistent with what I said. While f could be coded in a system that *required* termination, the outer loop could not. As I mentioned in a follow-up, event loop languages such as E enforce this program structure, which would almost or entirely eliminate the need for annotations in a type system that proves termination of some subprograms. -- David Hopwood [EMAIL PROTECTED] -- http://mail.python.org/mailman/listinfo/python-list
array manipulation without for loops
Hi, I have two arrays that are of the same dimension but having 3 different values: 255, 1 or 2. I would like to set all the positions in both arrays having 255 to be equal, i.e., where one array has 255, I set the same elements in the other array to 255 and visa versa. Does anyone know how to do this without using for loops? Sincerely, Sheldon -- http://mail.python.org/mailman/listinfo/python-list
languages with full unicode support
Languages with Full Unicode Support
As far as i know, Java and JavaScript are languages with full, complete
unicode support. That is, they allow names to be defined using unicode.
(the JavaScript engine used by FireFox support this)
As far as i know, here's few other lang's status:
C → No.
Python → No.
Perl → No.
Haskell → Yes by the spec, but no on existing compilers.
JavaScript → No in general. Firefox's engine do support it.
Lisps → No.
unix shells (bash) → No. (this probably applies to all unix shells)
Java → Yes and probably beats all. However, there may be a bug in 1.5
compiler.
Also, there appears to be a bug with Java 1.5's unicode support. The
following code compiles fine in 1.4, but under 1.5 the compiler
complains about the name x1.str★.
class 方 {
String str北 =
北方有佳人,絕世而獨立。\n一顧傾人城,再顧傾人国。\n寧不知倾城与倾国。\n佳人難再得。;
String str★=θπαβγλϕρκψ ≤≥≠≈⊂⊃⊆⊇∈
ⅇⅈⅉ∞∆° ℵℜℂℝℚℙℤ ℓ∟∠∡ ∀∃ ∫∑∏
⊕⊗⊙⊚⊛∘∙ ★☆;
}
class UnicodeTest {
public static void main(String[] arg) {
方 x1 = new 方();
System.out.println( x1.str北 );
System.out.println( x1.str★ );
}
}
If you know a lang that does full unicode support, please let me know.
Thanks.
Xah
[EMAIL PROTECTED]
∑ http://xahlee.org/
--
http://mail.python.org/mailman/listinfo/python-list
Re: array manipulation without for loops
Sheldon wrote: Hi, I have two arrays that are of the same dimension but having 3 different values: 255, 1 or 2. I would like to set all the positions in both arrays having 255 to be equal, i.e., where one array has 255, I set the same elements in the other array to 255 and visa versa. Does anyone know how to do this without using for loops? Sincerely, Sheldon Whatever for? Have you got something against for loops? However... You could roll you own loop: i=0 while i whatever: # ... do something with i i += 1 But what's the point? This does the same as a for loop but slower. If you don't want any kind of a loop (again, What's the point?) you could write something recursive: def proc(i, ...): # ... do something with i if i whatever: proc(i+1, ...) But this would be even slower. Gary Herron -- http://mail.python.org/mailman/listinfo/python-list
Re: What is Expressiveness in a Computer Language
Gabriel Dos Reis wrote: | | (Unfortunately, you can hardly write interesting programs in any safe | subset of C.) Fortunately, some people do, as living job. I don't think so. Maybe the question is what a safe subset consists of. In my book, it excludes all features that are potentially unsafe. So in particular, C-style pointers are out, because they can easily dangle, be uninitialisied, whatever. Can you write a realistic C program without using pointers? - Andreas -- http://mail.python.org/mailman/listinfo/python-list
Re: What is Expressiveness in a Computer Language
Chris F Clark (I) wrote: I'm particularly interested if something unsound (and perhaps ambiguous) could be called a type system. I definitely consider such things type systems. Marshall [EMAIL PROTECTED] wrote: I don't understand. You are saying you prefer to investigate the unsound over the sound? ... Again, I cannot understand this. In a technical realm, vagueness is the opposite of understanding. At the risk of injecting too much irrelevant philosophy into the discussion, I will with great trepdiation reply. First in the abstrtact: No, understanding is approximating. The world is inherently vague. We make false symbolic models of the world which are consistent, but at some level they do not reflect reality, because reality isn't consistent. Only by abtracting away the inherent infinite amout of subtlety present in the real universe can we come to comprehensible models. Those models can be consistent, but they are not the universe. The models in their consistency, prove things which are not true about the real universe. Now in the concrete: In my work productivity is ultimately important. Therefore, we live by the 80-20 rule in numerous variations. One of ths things we do to achieve productivity is simplify things. In fact, we are more interested in an unsound simplification that is right 80% of the time, but takes only 20% of the effort to compute, than a completely sound (100% right) model which takes 100% of the time to compute (which is 5 times as long). We are playing the probabilities. It's not that we don't respect the sound underpining, the model which is consistent and establishes certain truths. However, what we want is the rule of thumb which is far simpler and approximates the sound model with reasonable accuracy. In particular, we accept two types of unsoundness in the model. One, we accept a model which gives wrong answers which are detectable. We code tests to catch those cases, and use a different model to get the right answer. Two, we accept a model which gets the right answer only when over-provisioned. for example, if we know a loop will occassionaly not converge in the n-steps that it theoretically should, we will run the loop for n+m steps until the approximation also converges--even if that requires allocating m extra copies of some small element than are theoretically necessary. A small waste of a small resource, is ok if it saves a waste of a more critical resource--the most critical resource of all being our project timeliness. We do the same things in our abstract reasoning (including our type model). The problems we are solving are too large for us to understand. Therefore, we make simplifications, simplifications we know are inaccurate and potentially unsound. Our algorithm then solves the simplified model, which we think covers the main portion of the problem. It also attempts to detect when it has encountered a problem that is outside of the simplified region, on the edge so to speak. Now, in general, we can figure out how to handle certain edge cases, and we do it. However, some times the edge of one part of the algorithm intereacts with an edge of another part of the algorithm and we get a corner case. Because our model is too simple and the reasoning it allows is thus unsound, the algorithm will occassionally compute the wrong results for some of those corners. We use the same techniques for dealing with them. Dynamic tagging is one way of catching when we have gotten the wrong answer in our type simplification. Marshall's last point: I flipped a coin to see who would win the election; it came up Bush. Therefore I *knew* who was going to win the election before it happened. See the probem? Flipping one coin to determine an election is not playing the probabilities correctly. You need a plausible explanation for why the coin should predict the right answer and a track record of it being correct. If you had a coin that had correctly predicted the previous 42 presidencies and you had an explanation why the coin was right, then it would be credible and I would be willing to wager that it could also predict that the coin could tell us who the 44th president would be. One flip and no explanation is not sufficient. (And to the abstract point, to me that is all knowledge is, some convincing amount of examples and a plausible explanation--anyone who thinks they have more is appealing to a knowledge of the universe that I don't accept.) I do not want incredible unsound reasoning, just reasoning that is marginal, within a margin of safety that I can control. Everyone that I have know of has as far as I can tell made simplifying assumptions to make the world tractable. Very rarely do we deal with the world completely formally. Look at where that got Russell and Whitehead. I'm just trying to be honest about that fact and find ways to compensate for my own failures. -Chris -- http://mail.python.org/mailman/listinfo/python-list
Re: Python taught in schools?
MilkmanDan [EMAIL PROTECTED] wrote: I'll be a college freshman this fall, attending Florida Institute of Tech studying electrical engineering. I was considering taking some classes in programming and computer science, and I happened to notice that everything taught is using C++. After further research, it seems to me that C++ seems to be the dominating language in universities. Must be a weird local phenomenon -- my impression (based on non-scientific but widespread observations) is that _Java_ has come to dominate the programming-language scene in universities. One such observation struck me intensely last year, for example, as Tim O'Reilly was showing (at Euro OSCON 2005) his rich graphical environment for looking at book sales (by category, time, etc etc): Java book sales display an obvious, strong cyclic seasonality with a yearly cycle, in a perfect correlation with the times at which students would be likely to buy books. No other language whose book-sales data Tim displayed had anything like that obvious an effect (C, C++, Basic, Perl, Python, Ruby, ...); funny enough, Tim himself, while obviously seeing the seasonality (the UK-sales diagram in particular looked almost like a sine wave!-), hadn't thought of the student purchases explanation. For some reason, the effect, while obvious already in US data, was even more pronounced in UK data; perhaps UK universities have less flexible timing c for courses (I don't know much about UK universities -- I do know, however, that in Italy for example summer courses for undergrads are rare to non-existent, while I see there's quite an offer of those in the US). Many others have remarked on Java's ascendancy as a language in universities in many different contexts. Joel Spolski, for example, has bemoaned that ascendancy's effect on how well he can evaluate a new grad in a hiring interview: when undegrads typically learned C or Lisp, he says, he had sure-fire ways to probe if a candidate has what it takes to be a top programmer, by asking hard questions respectively on pointers and on recursion; with everybody learning Java, he's lost that chance, because a candidate may never have seen pointers and be quite unfamiliar with recursion (supported in Java, of course, but hardly the staple it is in Lisp!-), so poor performance on such questions does not really indicate much:-). Paul Graham, a paladin of Lisp, created quite a stir by stating that you're likely to get better programmers if you look for ones experienced in Python rather than ones experienced in Java; in the midst of the resulting flamefest, he clarified that the issue is not so much about the specific nature of the languages (although, like many Lisp'ers, he finds Python a lesser evil than Java, technically) -- rather, he says that a programmer who's only experienced in Java may have merely fallen into it because that's what universities teach and he or she had no motivation to look elsewhere and thus probably no deep passion for programming, while somebody experienced in Python (which is not as widely taught) must have taked that path by choice, evidencing a real passion for programming (by looking around and choosing reasonably well -- of course, for Graham, only Lisp would be the perfect choice;-). A similar line of reasoning has been used to explain the empirical findings of Software Development magazine's yearly survey on programmers' salaries, which, for years, has shown Python programmers at the top of the heap and Visual Basic programmers at the bottom (I do not recall where Java programmers place, but I think it's closer to the bottom than to the top): VB programmers, goes the reasoning, are closer to have stumbled into it and to have no real experience of other languages, while Python programmers typically have strong experience in more languages and use Python _by choice_ -- so, again (the reasoning goes), it's not so much about the languages per se, but the sociology and psychology around them. ((in terms of the emerging economics discipline of asymmetric information markets, this would make Python expertise a signal of a strong programmer in a way that VB or to a lesser extent Java would not)). By comparison, our local community college teaches a few classes in VB, Java, Javascript, C++, and for some reason, PASCAL. Interestingly, Mission College (Santa Clara, CA) offers C (I know because my wife's been studying there to accumulate some credits while Stanford considered her application -- it's now been accepted, so she'll be starting Symbolic Systems there in the fall); Bologna University (I know the details because of the recent study there of my son [Financial Economics], daughter [Telecom Engineering] and daughter's boyfriend [started with Civil Engineering, switched to Political Science] offers: a first course in C, and a second one in Java, for Telecom; Fortran, for Civil engineers (all of these are mandatory for these majors); no mandatory programming for
Re: Python taught in schools?
MilkmanDan wrote: I'll be a college freshman this fall, attending Florida Institute of Tech studying electrical engineering. I was considering taking some classes in programming and computer science, and I happened to notice that everything taught is using C ++. After further research, it seems to me that C++ seems to be the dominating language in universities. Actually, I think Java is the most commonly used language in the CS1, although C++ may be more popular at engineering institutions. By comparison, our local community college teaches a few classes in VB, Java, Javascript, C++, and for some reason, PASCAL. I'm certianly not against any of this, but out of curiousity does anyone know of a school that teaches Python? See the following for a list compiled from responses on the python- edu list. http://studypack.com/comp/mod/glossary/view.php?id=2835 Dave -- http://mail.python.org/mailman/listinfo/python-list
Re: languages with full unicode support
Xah Lee wrote: Lisps → No. The Common Lisp spec (CLHS) doesn't require that implementations support Unicode characters, but it doesn't forbid it and some implementations support it, e.g. http://clisp.cons.org/impnotes.html -- Frank Buss, [EMAIL PROTECTED] http://www.frank-buss.de, http://www.it4-systems.de -- http://mail.python.org/mailman/listinfo/python-list
Re: array manipulation without for loops
Hi Gary, I am really trying to cut the time down as I have 600+ arrays with dimensions (1215,1215) to compare and I do a lot more things with the arrays. If I understand you correctly, there is no way around a for loop? /Sheldon Gary Herron wrote: Sheldon wrote: Hi, I have two arrays that are of the same dimension but having 3 different values: 255, 1 or 2. I would like to set all the positions in both arrays having 255 to be equal, i.e., where one array has 255, I set the same elements in the other array to 255 and visa versa. Does anyone know how to do this without using for loops? Sincerely, Sheldon Whatever for? Have you got something against for loops? However... You could roll you own loop: i=0 while i whatever: # ... do something with i i += 1 But what's the point? This does the same as a for loop but slower. If you don't want any kind of a loop (again, What's the point?) you could write something recursive: def proc(i, ...): # ... do something with i if i whatever: proc(i+1, ...) But this would be even slower. Gary Herron -- http://mail.python.org/mailman/listinfo/python-list
Re: What is Expressiveness in a Computer Language
Joachim Durchholz [EMAIL PROTECTED] wrote: Sorry, I have to insist that it's not me who's stretching terms here. All textbook definitions that I have seen define a type as the set/operations/axioms triple I mentioned above. No mention of immutability, at least not in the definitions. The immutability comes from the fact (perhaps implicit in these textbooks, or perhaps they are not really texts on formal type theory) that types are assigned to expressions, and the program is not likely to change as it executes. Even such oddities as self-modifying code are generally formally modeled as a single program, which reduces to other programs as it evaluates just like everything else. The original program doesn't change in the formal model. Hence the common (and, I think, meaningless) distinction that has been made here: that static type systems assign types to expressions (sometimes I hear variables, which is limiting and not really correct), while dynamic type systems do so to values. However, that falls apart when you understand what formal type systems mean by types. What they mean, roughly, is that label which we attach to an expressions according to fixed rules to help facilitate our proofs. Since dynamic type systems don't do such proofs, I'm having trouble understanding what could possibly be meant by assigning types to values, unless we redefine type. That's what I've been trying to do. So far I've had only limited success, although there is definite potential in one post by Chris Uppal and another by Chris Clark (or maybe I'm just partial to other people named Chris). -- Chris Smith - Lead Software Developer / Technical Trainer MindIQ Corporation -- http://mail.python.org/mailman/listinfo/python-list
Re: HTTP server
placid wrote: Simon Forman wrote: ... For what you're asking about you'd probably want to use the CGIHTTPRequestHandler from the CGIHTTPServer module instead. Check out http://docs.python.org/lib/module-CGIHTTPServer.html This is what i was after, thanks for the tip. You're welcome, my pleasure. : ) ... Im having trouble running the following cgi script on windows code #!c:/Python/python.exe -u text = Content-type: text/html TITLE CGI 101 /TITLE H1A Second CGI script/H1 HR PHello, CGI World!/P print text /code using this http server from http://effbot.org/librarybook/cgihttpserver.htm code import CGIHTTPServer import BaseHTTPServer class Handler(CGIHTTPServer.CGIHTTPRequestHandler): cgi_directories = [/cgi] PORT = 8000 httpd = BaseHTTPServer.HTTPServer((, PORT), Handler) print serving at port, PORT httpd.serve_forever() /code i get the error number 403, when i try to access the cgi script which is located in a subdirectory called cgi where this file is (http server). I have a feeling that i need to change the Handler class or something, implement , but i couldnt find any examples other then this from eff-bot. It could also be this line of code, that a google search turned up, its the way of running cgi scripts on windows #!c:/Python/python.exe -u Cheers Your cgi and server scripts look fine to me. Some diagnostic questions: What is the filename of your cgi script? (It must end in .py or .pyw for CGIHTTPRequestHandler to recognize it as a python script. See the is_python() method in the handler class. Also, in this case the #!c:/Python/python.exe -u line isn't needed, but it doesn't hurt. CGIHTTPRequestHandler should find the python interpreter for you without it.) What was the exact URL that you're using to try to reach your script? (It should look something like: http://localhost:8000/cgi/myscript.py;) What was the error message that accompanied the 403 error? Did you start the server script from the directory it's in? What was the log output from your server script when you tried to access the cgi script? Peace, ~Simon -- http://mail.python.org/mailman/listinfo/python-list
Re: What is Expressiveness in a Computer Language
[EMAIL PROTECTED] writes: | Gabriel Dos Reis wrote: | | | | (Unfortunately, you can hardly write interesting programs in any safe | | subset of C.) | | Fortunately, some people do, as living job. | | I don't think so. Maybe the question is what a safe subset consists | of. In my book, it excludes all features that are potentially unsafe. if you equate unsafe with potentially unsafe, then you have changed gear and redefined things on the fly, and things that could be given sense before ceases to have meaning. I decline following such an uncertain, extreme, path. | So in particular, C-style pointers are out, because they can easily | dangle, be uninitialisied, whatever. sorry, the specific claim I was responding to is not whether *you* can easily misuse C constructs. I would refrain from generalizing your inability to write interesting correct programs in C, to a quality of the language itself. Rather, the claim I was responding to is this: (Unfortunately, you can hardly write interesting programs in any safe subset of C.) I would suggest you give more thoughts to the claims made in http://www.seas.upenn.edu/~sweirich/types/archive/1999-2003/msg00298.html -- Gaby -- http://mail.python.org/mailman/listinfo/python-list
Re: array manipulation without for loops
Sheldon [EMAIL PROTECTED] wrote: I have two arrays that are of the same dimension but having 3 different values: 255, 1 or 2. I would like to set all the positions in both arrays having 255 to be equal, i.e., where one array has 255, I set the same elements in the other array to 255 and visa versa. Does anyone know how to do this without using for loops? Python's Numeric extension package (still available, but not actively developed any more) and its successors (numarray, and the even newer numpy) are replete with such functionality -- indeed, to really use arrays in Python you should get any one of these packages (Python offers arrays only in the very limited incarnation of the standard library module named array -- better than nothing, but little built-in functionality, while those packages have plenty). Of course, if you say array when actually you mean list, the situation is completely different (it may be worth turning list into Numeric arrays for manipulation, then back when you're done, if speed is absolutely of the essence and you desperately need lists as inputs and outputs but a lot of manipulation in-between). Alex -- http://mail.python.org/mailman/listinfo/python-list
Re: array manipulation without for loops
Sheldon [EMAIL PROTECTED] wrote: Hi Gary, I am really trying to cut the time down as I have 600+ arrays with dimensions (1215,1215) to compare and I do a lot more things with the arrays. If I understand you correctly, there is no way around a for loop? In pure Python (w/o extension packages) there are no 2-D arrays; so either you're using lists of lists (and I wonder how you fit even one of them in memory, if they're 1215 by 1215, much less 600!) or you're already using some extension (Numeric, numarray, numpy) and aren't telling us which one. If you're using pure Python add your extension of choice, if you're using an extension already tell us which one, and in each case there will be ways to perform your manipulation tasks faster than Python-level for loops would afford. Alex -- http://mail.python.org/mailman/listinfo/python-list
Re: array manipulation without for loops
Sheldon wrote: Hi Gary, I am really trying to cut the time down as I have 600+ arrays with dimensions (1215,1215) to compare and I do a lot more things with the arrays. If I understand you correctly, there is no way around a for loop? Well no. I gave you two alternatives to for loops. But once we learn that your motivation is speed on large arrays, then, by all means, go with Alex's suggestion. Use numpy (or one if its earlier incarnations). See: http://numeric.scipy.org/ This is a HIGHLY efficient implementation of arrays for Python. It provides a number of very general operations that can be performed across arrays. Good luck Gary Herron /Sheldon Gary Herron wrote: Sheldon wrote: Hi, I have two arrays that are of the same dimension but having 3 different values: 255, 1 or 2. I would like to set all the positions in both arrays having 255 to be equal, i.e., where one array has 255, I set the same elements in the other array to 255 and visa versa. Does anyone know how to do this without using for loops? Sincerely, Sheldon Whatever for? Have you got something against for loops? However... You could roll you own loop: i=0 while i whatever: # ... do something with i i += 1 But what's the point? This does the same as a for loop but slower. If you don't want any kind of a loop (again, What's the point?) you could write something recursive: def proc(i, ...): # ... do something with i if i whatever: proc(i+1, ...) But this would be even slower. Gary Herron -- http://mail.python.org/mailman/listinfo/python-list
Re: What is Expressiveness in a Computer Language
[EMAIL PROTECTED] wrote: Huh? There is a huge, fundamental difference: namely whether a type system is sound or not. A soundness proof is obligatory for any serious type theory, and failure to establish it simply is a bug in the theory. So you claim Java and Objective C are simply bugs in the theory. --Scott David Daniels [EMAIL PROTECTED] -- http://mail.python.org/mailman/listinfo/python-list
Re: array manipulation without for loops
Alex, I am using Numeric and have created 3 arrays: zero((1215,1215),Float) Two arrays are compared and one is used to hold the mean difference between the two compared arrays. Then I compare 290 or 340 pairs of arrays. I know that memory is a problem and that is why I don't open all of these arrays at the same time. I cannot install Numpy due to my working conditions. Sorry I should have made it clear that is was Numeric I was working with. /Sheldon Alex Martelli wrote: Sheldon [EMAIL PROTECTED] wrote: Hi Gary, I am really trying to cut the time down as I have 600+ arrays with dimensions (1215,1215) to compare and I do a lot more things with the arrays. If I understand you correctly, there is no way around a for loop? In pure Python (w/o extension packages) there are no 2-D arrays; so either you're using lists of lists (and I wonder how you fit even one of them in memory, if they're 1215 by 1215, much less 600!) or you're already using some extension (Numeric, numarray, numpy) and aren't telling us which one. If you're using pure Python add your extension of choice, if you're using an extension already tell us which one, and in each case there will be ways to perform your manipulation tasks faster than Python-level for loops would afford. Alex -- http://mail.python.org/mailman/listinfo/python-list
Re: array manipulation without for loops
I have two arrays that are of the same dimension but having 3 different values: 255, 1 or 2. I would like to set all the positions in both arrays having 255 to be equal, i.e., where one array has 255, I set the same elements in the other array to 255 and visa versa. Does anyone know how to do this without using for loops? # make some sample data c = 20 import random, itertools a1 = [(1,2,255)[random.randint(0,2)] for x in xrange(c)] a2 = [(1,2,255)[random.randint(0,2)] for x in xrange(c)] # actually do the work all = [(x==255 or y==255) and (255, 255) or (x,y) for (x,y) in itertools.izip(a1,a2)] b1 = [x[0] for x in all] b2 = [x[1] for x in all] a1, a2 = b1, b2 # if you want them to replace the originals Seems to do what I understand that you're describing using no loops (other than those implied by list comprehension). There may be some nice pythonic way to unzip a list of tuples created by zip() but I couldn't scare up such a method, and searching for unzip turned up a blizzard of hits for dealing with ZIP files, not for unzipping that which was previously zip()'ed. My google-foo must be broken. :) Otherwise, you could just do b1,b2 = magic_unzip([(x==255 or y==255) and (255, 255) or (x,y) for (x,y) in itertools.izip(a1,a2)]) or a1,a2 = magic_unzip([(x==255 or y==255) and (255, 255) or (x,y) for (x,y) in itertools.izip(a1,a2)]) if you just want to dispose of your originals. -tkc -- http://mail.python.org/mailman/listinfo/python-list
Re: error with string (beginner)
In article [EMAIL PROTECTED], Alex Pavluck [EMAIL PROTECTED] wrote: Hello. I get the following error with the following code. Is there something wrong with my Python installation? code: import types something = input(Enter something and I will tell you the type: ) if type(something) is types.IntType: print you entered an integer elif type(something) is types.StringType: print you entered a string error: String: Source for exec/eval is unavailable There are several things wrong--'least three distinct ones, by my count. What version of Python do you believe you're using? What input do you enter at the Enter something ... prompt? I suspect you're going to have happier results all around when you replace input with raw_input. I encourage you to read the documenta- tion for each. -- http://mail.python.org/mailman/listinfo/python-list
Re: Python taught in schools?
I think there is a Python club at UCF, Orlandomight help you indirectly. MilkmanDan wrote: I'll be a college freshman this fall, attending Florida Institute of Tech studying electrical engineering. I was considering taking some classes in programming and computer science, and I happened to notice that everything taught is using C++. After further research, it seems to me that C++ seems to be the dominating language in universities. By comparison, our local community college teaches a few classes in VB, Java, Javascript, C++, and for some reason, PASCAL. I'm certianly not against any of this, but out of curiousity does anyone know of a school that teaches Python? -- http://mail.python.org/mailman/listinfo/python-list
Re: Python taught in schools?
I replied to a wrong post. My bad.I know for sure that there is some kinda Python Club at UCF Orlando. There is Prof called Michael Johnson who teaches Physics gives you an intro to Python. http://www.physics.ucf.edu/~mdj/MinimalPython.html Good Luck -- http://mail.python.org/mailman/listinfo/python-list
Re: What is Expressiveness in a Computer Language
Joachim Durchholz wrote: Anton van Straaten schrieb: It seems we have languages: with or without static analysis with or without runtime type information (RTTI or tags) with or without (runtime) safety with or without explicit type annotations with or without type inference Wow. And I don't think that's a complete list, either. Yup. What else? (Genuinely curious.) I left off a big one: nominal vs. structural Also: has subtyping polymorphism or not, has parametric polymorphism or not. Marshall -- http://mail.python.org/mailman/listinfo/python-list
Re: What is Expressiveness in a Computer Language
Anton van Straaten [EMAIL PROTECTED] wrote: The problem is that there are no useful sound definitions for the type systems (in the static sense) of dynamically-typed languages. Yet, we work with type-like static properties in those languages all the time, as I've been describing. I honestly don't find it very compelling that there are similarities between the kinds of reasoning that goes on in static type systems versus those used by programmers in dynamically typed languages. Rather, of course there are similarities. It would be shocking if there were not similarities. These similarities, though, have nothing to with the core nature of types. Basically, there are ways to reason about programs being correct. Static type systems describe their reasoning (which is always axiomatic in nature) by assigning types to expressions. Programmers in dynamically typed languages still care about the correctness of their programs, though, and they find ways to reason about their programs as well. That reasoning is not completely axiomatic, but we spend an entire lifetime applying this basic logical system, and it makes sense that programmers would try to reason from premises to conclusions in ways similar to a type system. Sometimes they may even ape other type systems with which they are familiar; but even a programmer who has never worked in a typed language would apply the same kind of logic as is used by type systems, because it's a form of logic with which basically all human beings are familiar and have practiced since the age of three (disclaimer: I am not a child psychologist). On the other hand, programmers don't restrict themselves to that kind of pure axiomatic logic (regardless of whether the language they are working in is typed). The also reason inductively -- in the informal sense -- and are satisfied with the resulting high probabilities. They generally apply intuitions about a problem statement that is almost surely not written clearly enough to be understood by a machine. And so forth. What makes static type systems interesting is not the fact that these logical processes of reasoning exist; it is the fact that they are formalized with definite axioms and rules of inference, performed entirely on the program before execution, and designed to be entirely evaluatable in finite time bounds according to some procedure or set of rules, so that a type system may be checked and the same conclusion reached regardless of who (or what) is doing the checking. All that, and they still reach interesting conclusions about programs. If informal reasoning about types doesn't meet these criteria (and it doesn't), then it simply doesn't make sense to call it a type system (I'm using the static terminology here). It may make sense to discuss some of the ways that programmer reasoning resembles types, if indeed there are resemblances beyond just that they use the same basic rules of logic. It may even make sense to try to identify a subset of programmer reasoning that even more resembles... or perhaps even is... a type system. It still doesn't make sense to call programmer reasoning in general a type system. In the same post here, you simultaneously suppose that there's something inherently informal about the type reasoning in dynamic languages; and then talk about the type system in the static sense of a dynamic language. How is this possibly consistent? We know that we can easily take dynamically-typed program fragments and assign them type schemes, and we can make sure that the type schemes that we use in all our program fragments use the same type system. Again, it would be surprising if this were not true. If programmers do, in fact, tend to reason correctly about their programs, then one would expect that there are formal proofs that could be found that they are right. That doesn't make their programming in any way like a formal proof. I tend to think that a large number of true statements are provable, and that programmers are good enough to make a large number of statements true. Hence, I'd expect that it would be possible to find a large number of true, provable statements in any code, regardless of language. So we actually have quite a bit of evidence about the presence of static types in dynamically-typed programs. No. What we have is quite a bit of evidence about properties remaining true in dynamically typed programs, which could have been verified by static typing. We're currently discussing something that so far has only been captured fairly informally. If we restrict ourselves to only what we can say about it formally, then the conversation was over before it began. I agree with that statement. However, I think the conversation regarding static typing is also over when you decide that the answer is to weaken static typing until the word applies to informal reasoning. If the goal isn't to reach a
Re: What is Expressiveness in a Computer Language
Scott David Daniels wrote: [EMAIL PROTECTED] wrote: Huh? There is a huge, fundamental difference: namely whether a type system is sound or not. A soundness proof is obligatory for any serious type theory, and failure to establish it simply is a bug in the theory. So you claim Java and Objective C are simply bugs in the theory. They are certainly off topic in CLPM. jue -- http://mail.python.org/mailman/listinfo/python-list
Re: Eclipse IDE question
kilnhead wrote: I am trying to use eclipse for python development. Is it possible to run a python script without having to name/setup a configuration? Can eclipse be set up so that run loads the code into the interpreter and goes? I don't want to create a new run config every time I want to run a script. try pydev , a plugin for eclipse -- http://mail.python.org/mailman/listinfo/python-list
Re: array manipulation without for loops
Sheldon [EMAIL PROTECTED] wrote: Alex, I am using Numeric and have created 3 arrays: zero((1215,1215),Float) Two arrays are compared and one is used to hold the mean difference between the two compared arrays. Then I compare 290 or 340 pairs of arrays. I know that memory is a problem and that is why I don't open all of these arrays at the same time. I cannot install Numpy due to my working conditions. Sorry I should have made it clear that is was Numeric I was working with. It's OK, even if the hard-core numeric-python people are all evangelizing for migration to numpy (for reasons that are of course quite defensible!), I think it's quite OK to stick with good old Numeric for the moment (and that's exactly what I do for my own personal use!). So, anyway, I'll assume you mean your 1215 x 1215 arrays were created by calling Numeric.zeros, not zero (with no trailing s) which is a name that does not exists in Numeric. Looking back to your original post, let's say that you have two such arrays, a and b, both 1215x1215 and of Numeric.Float type, and the entries of each array are all worth 1, 2, or 255 (that's how I read your original post; if that's not the case, please specify). We want to write a function that alters both a and b, specifically setting to 255 all entries in each array whose corresponding entries are 255 in the other array. Now that's pretty easy -- for example: import Numeric def equalize(a, b, v=255): Numeric.putmask(a, b==v, v) Numeric.putmask(b, a==v, v) if __name__ == '__main__': a = Numeric.zeros((5,5), Numeric.Float) b = Numeric.zeros((5,5), Numeric.Float) a[1,2]=a[2,1]=b[3,4]=b[0,2]=255 a[3,0]=a[0,0]=1 b[0,3]=b[4,4]=2 print Before: print a print b equalize(a, b) print After: print a print b brain:~/pynut alex$ python ab.py Before: [[ 1.0.0.0.0.] [ 0.0. 255.0.0.] [ 0. 255.0.0.0.] [ 1.0.0.0.0.] [ 0.0.0.0.0.]] [[ 0.0. 255.2.0.] [ 0.0.0.0.0.] [ 0.0.0.0.0.] [ 0.0.0.0. 255.] [ 0.0.0.0.2.]] After: [[ 1.0. 255.0.0.] [ 0.0. 255.0.0.] [ 0. 255.0.0.0.] [ 1.0.0.0. 255.] [ 0.0.0.0.0.]] [[ 0.0. 255.2.0.] [ 0.0. 255.0.0.] [ 0. 255.0.0.0.] [ 0.0.0.0. 255.] [ 0.0.0.0.2.]] brain:~/pynut alex$ Of course I'm using tiny arrays here, for speed of running and ease of display and eyeball-checking, but everything should work just as well in your case. Care to check and let us know? Numeric has pretty good documentation (numpy's is probably even better, but it is not available for free, so I don't know!), and if you don't find that documentation sufficient you might want to have a look to my book Python in a Nutshell which devotes a chapter to Numeric (it also is not available for free, but you can get a subscription to O'Reilly's Safari online-books repository, which is free for the first two weeks, and lets you look at many books including Python in a Nutshell -- if you don't want to pay monthly subscription fees, make sure you cancel your trial subscription before two weeks have passed!!!). I strongly recommend that, in some way or other, you DO get a taste of the huge amount of functionality that Numeric provides for you -- with the size of computational tasks you're talking about, an investment of 2-3 hours spent becoming deeply familiar with everything Numeric offers may well repay itself in savings of ten times as much execution time, and what other investments offer such ROI as 1000%?-) Alex -- http://mail.python.org/mailman/listinfo/python-list
Re: array manipulation without for loops
Tim Chase [EMAIL PROTECTED] wrote:
...
all = [(x==255 or y==255) and (255, 255) or (x,y) for (x,y)
in itertools.izip(a1,a2)]
b1 = [x[0] for x in all]
b2 = [x[1] for x in all]
a1, a2 = b1, b2 # if you want them to replace the originals
Seems to do what I understand that you're describing using no
loops (other than those implied by list comprehension).
Yep, but the performance cost of the for-loops in the comprehension is
essentially the same as for such loops written normally.
There may be some nice pythonic way to unzip a list of tuples
created by zip() but I couldn't scare up such a method, and
Perhaps what you have in mind is:
a=zip('feep','grol')
a
[('f', 'g'), ('e', 'r'), ('e', 'o'), ('p', 'l')]
zip(*a)
[('f', 'e', 'e', 'p'), ('g', 'r', 'o', 'l')]
But this wouldn't help the OP all that much with his performance
problems with large 2-D arrays (though it required some guessing to
gauge that it _was_ Numeric arrays that he was dealing with;-),
Alex
--
http://mail.python.org/mailman/listinfo/python-list
Re: Saying latently-typed language is making a category mistake
Chris Uppal wrote: It seems to me that most (all ? by definition ??) kinds of reasoning where we want to invoke the word type tend to have a form where we reduce values (and other things we want to reason about) to equivalence classes[*] w.r.t the judgements we wish to make, and (usually) enrich that structure with more-or-less stereotypical rules about which classes are substitutable for which other ones. So that once we know what type something is, we can short-circuit a load of reasoning based on the language semantics, by translating into type-land where we already have a much simpler calculus to guide us to the same answer. (Or representative symbols, or... The point is just that we throw away the details which don't affect the judgements.) One question: is this more specific than simply saying that we use predicate logic? A predicate divides a set into two subsets: those elements for which the predicate is true, and those for which it is false. If we then apply axioms or theorems of the form P(x) - Q(x), then we are reasoning from an equivalence class, throwing away the details we don't care about (anything that's irrelevant to the predicate), and applying stereotypical rules (the theorem or axiom). I don't quite understand what you mean by substituting classes. -- Chris Smith - Lead Software Developer / Technical Trainer MindIQ Corporation -- http://mail.python.org/mailman/listinfo/python-list
Re: What is Expressiveness in a Computer Language
Chris Smith schrieb: Joachim Durchholz [EMAIL PROTECTED] wrote: Sorry, I have to insist that it's not me who's stretching terms here. All textbook definitions that I have seen define a type as the set/operations/axioms triple I mentioned above. No mention of immutability, at least not in the definitions. The immutability comes from the fact (perhaps implicit in these textbooks, or perhaps they are not really texts on formal type theory) that types are assigned to expressions, That doesn't *define* what's a type or what isn't! If it's impossible to assign types to all expressions of a program in a language, that does mean that there's no useful type theory for the program, but it most definitely does not mean that there are no types in the program. I can still sensibly talk about sets of values, sets of allowable operations over each value, and about relationships between inputs and outputs of these operations. So programs have types, even if they don't have a static type system. Q.E.D. Regards, Jo -- http://mail.python.org/mailman/listinfo/python-list
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Re: array manipulation without for loops
Hi Alex, I will code this in a little while and get back to you. Terrific! I saw this function but I skipped over it without realizing what it could do. The Numeric doc is not very good and I am just getting into Python so your book sounds great especially since it covers Numeric. I will look into it when I get back to work tomorrow. Bye for now, Sheldon Alex Martelli wrote: Sheldon [EMAIL PROTECTED] wrote: Alex, I am using Numeric and have created 3 arrays: zero((1215,1215),Float) Two arrays are compared and one is used to hold the mean difference between the two compared arrays. Then I compare 290 or 340 pairs of arrays. I know that memory is a problem and that is why I don't open all of these arrays at the same time. I cannot install Numpy due to my working conditions. Sorry I should have made it clear that is was Numeric I was working with. It's OK, even if the hard-core numeric-python people are all evangelizing for migration to numpy (for reasons that are of course quite defensible!), I think it's quite OK to stick with good old Numeric for the moment (and that's exactly what I do for my own personal use!). So, anyway, I'll assume you mean your 1215 x 1215 arrays were created by calling Numeric.zeros, not zero (with no trailing s) which is a name that does not exists in Numeric. Looking back to your original post, let's say that you have two such arrays, a and b, both 1215x1215 and of Numeric.Float type, and the entries of each array are all worth 1, 2, or 255 (that's how I read your original post; if that's not the case, please specify). We want to write a function that alters both a and b, specifically setting to 255 all entries in each array whose corresponding entries are 255 in the other array. Now that's pretty easy -- for example: import Numeric def equalize(a, b, v=255): Numeric.putmask(a, b==v, v) Numeric.putmask(b, a==v, v) if __name__ == '__main__': a = Numeric.zeros((5,5), Numeric.Float) b = Numeric.zeros((5,5), Numeric.Float) a[1,2]=a[2,1]=b[3,4]=b[0,2]=255 a[3,0]=a[0,0]=1 b[0,3]=b[4,4]=2 print Before: print a print b equalize(a, b) print After: print a print b brain:~/pynut alex$ python ab.py Before: [[ 1.0.0.0.0.] [ 0.0. 255.0.0.] [ 0. 255.0.0.0.] [ 1.0.0.0.0.] [ 0.0.0.0.0.]] [[ 0.0. 255.2.0.] [ 0.0.0.0.0.] [ 0.0.0.0.0.] [ 0.0.0.0. 255.] [ 0.0.0.0.2.]] After: [[ 1.0. 255.0.0.] [ 0.0. 255.0.0.] [ 0. 255.0.0.0.] [ 1.0.0.0. 255.] [ 0.0.0.0.0.]] [[ 0.0. 255.2.0.] [ 0.0. 255.0.0.] [ 0. 255.0.0.0.] [ 0.0.0.0. 255.] [ 0.0.0.0.2.]] brain:~/pynut alex$ Of course I'm using tiny arrays here, for speed of running and ease of display and eyeball-checking, but everything should work just as well in your case. Care to check and let us know? Numeric has pretty good documentation (numpy's is probably even better, but it is not available for free, so I don't know!), and if you don't find that documentation sufficient you might want to have a look to my book Python in a Nutshell which devotes a chapter to Numeric (it also is not available for free, but you can get a subscription to O'Reilly's Safari online-books repository, which is free for the first two weeks, and lets you look at many books including Python in a Nutshell -- if you don't want to pay monthly subscription fees, make sure you cancel your trial subscription before two weeks have passed!!!). I strongly recommend that, in some way or other, you DO get a taste of the huge amount of functionality that Numeric provides for you -- with the size of computational tasks you're talking about, an investment of 2-3 hours spent becoming deeply familiar with everything Numeric offers may well repay itself in savings of ten times as much execution time, and what other investments offer such ROI as 1000%?-) Alex -- http://mail.python.org/mailman/listinfo/python-list
Re: What is Expressiveness in a Computer Language
Gabriel Dos Reis wrote: [EMAIL PROTECTED] writes: | Gabriel Dos Reis wrote: | | | | (Unfortunately, you can hardly write interesting programs in any safe | | subset of C.) | | Fortunately, some people do, as living job. | | I don't think so. Maybe the question is what a safe subset consists | of. In my book, it excludes all features that are potentially unsafe. if you equate unsafe with potentially unsafe, then you have changed gear and redefined things on the fly, and things that could be given sense before ceases to have meaning. I decline following such an uncertain, extreme, path. An unsafe *feature* is one that can potentially exhibit unsafe behaviour. How else would you define it, if I may ask? A safe *program* may or may not use unsafe features, but that is not the point when we talk about safe *language subsets*. I would suggest you give more thoughts to the claims made in http://www.seas.upenn.edu/~sweirich/types/archive/1999-2003/msg00298.html Thanks, I am aware of it. Taking into account the hypothetical nature of the argument, and all the caveats listed with respect to C, I do not think that it is too relevant for the discussion at hand. Moreover, Harper talks about a relative concept of C-safety. I assume that everybody here understands that by safe in this discussion we mean something else (in particular, memory safety). Or are you trying to suggest that we should indeed consider C safe for the purpose of this discussion? - Andreas -- http://mail.python.org/mailman/listinfo/python-list
Re: sum fonction in gadfly
jean-jeanot wrote: Thank you for your help. You're welcome. It could be useful for me to change of DB ? Which one ? Postgresql or another ? Well, if gadfly is serving you well, you might as well stay with it. Python 2.5 comes with sqlite3, which might well be a nice small step. I find Postgresql to be a real solid DB, and a company I've been talking with likes MySQL -- which finally has transactions (one of my personal requirements before I'll call a DBMS real). Really, you should decide what you want the DBMS to do, and try to get those requirements out; you'll get better advice. --Scott David Daniels [EMAIL PROTECTED] -- http://mail.python.org/mailman/listinfo/python-list
Re: What is Expressiveness in a Computer Language
[EMAIL PROTECTED] schrieb: Joachim Durchholz write: Another observation: type safeness is more of a spectrum than a clearcut distinction. Even ML and Pascal have ways to circumvent the type system, No. I'm not sure about Pascal, You'd have to use an untagged union type. It's the standard maneuver in Pascal to get unchecked bitwise reinterpretation. Since it's an undefined behavior, you're essentially on your own, but in practice, any compilers that implemented a different semantics were hammered with bug reports until they complied with the standard - in this case, an unwritten (and very unofficial) one, but a rather effective one. but (Standard) ML surely has none. NLFFI? Same with Haskell as defined by its spec. Um... I'm not 100% sure, but I dimly (mis?)remember having read that UnsafePerformIO also offered some ways to circumvent the type system. (Not that this would be an important point anyway.) OCaml has a couple of clearly marked unsafe library functions, but no unsafe feature in the language semantics itself. If there's a library with not-typesafe semantics, then at least that language implementation is not 100% typesafe. If all implementations of a language are not 100% typesafe, then I cannot consider the language itself 100% typesafe. Still, even Pascal is quite a lot more typesafe than, say, C. and even C is typesafe unless you use unsafe constructs. Tautology. Every language is safe unless you use unsafe constructs. No tautology - the unsafe constructs aren't just typewise unsafe ;-p That's exactly why I replaced Luca Cardelli's safe/unsafe typesafe/not typesafe. There was no definition to the original terms attached, and this discussion is about typing anyway. (Unfortunately, you can hardly write interesting programs in any safe subset of C.) Now that's a bold claim that I'd like to see substantiated. IOW from a type-theoretic point of view, there is no real difference between their typesafe and not typesafe languages in the statically typed column; the difference is in the amount of unsafe construct usage in practial programs. Huh? There is a huge, fundamental difference: namely whether a type system is sound or not. I think you're overstating the case. In type theory, of course, there's no such things as an almost typesafe language - it's typesafe or it isn't. In practice, I find no implementation where type mismatches cannot occur, if only when interfacing with the external world (except if you cheat by treating everything external as a byte sequence, which is like saying that all languages have at least a universal ANY type and are hence statically-typed). And in those languages that do have type holes, these holes may be more or less relevant - and it's a *very* broad spectrum here. And from that perspective, if ML indeed has no type hole at all, then it's certainly an interesting extremal point, but I still have a relevant spectrum down to assembly language. Regards, Jo -- http://mail.python.org/mailman/listinfo/python-list
Re: What is Expressiveness in a Computer Language
Scott David Daniels wrote: [EMAIL PROTECTED] wrote: Huh? There is a huge, fundamental difference: namely whether a type system is sound or not. A soundness proof is obligatory for any serious type theory, and failure to establish it simply is a bug in the theory. So you claim Java and Objective C are simply bugs in the theory. You're misquoting me. What I said is that lack of soundness of a particular type theory (i.e. a language plus type system) is a bug in that theory. But anyway, Java in fact is frequently characterised as having a bogus type system (e.g. with respect to array subtyping). Of course, in a hybrid language like Java with its dynamic checks it can be argued either way. Naturally, the type system of Objective-C is as broken as the one of plain C. - Andreas -- http://mail.python.org/mailman/listinfo/python-list
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Re: What is Expressiveness in a Computer Language
[EMAIL PROTECTED] schrieb: Gabriel Dos Reis wrote: | | (Unfortunately, you can hardly write interesting programs in any safe | subset of C.) Fortunately, some people do, as living job. I don't think so. Maybe the question is what a safe subset consists of. In my book, it excludes all features that are potentially unsafe. Unless you define safe, *any* program is unsafe. Somebody could read the program listing, which could trigger a traumatic childhood experiece. (Yes, I'm being silly. But the point is very serious. Even with less silly examples, whether a language or subset is safe entirely depends on what you define to be safe, and these definitions tend to vary vastly across language communities.) Regards, Jo -- http://mail.python.org/mailman/listinfo/python-list
Re: What is Expressiveness in a Computer Language
Pascal Costanza schrieb: Another observation: type safeness is more of a spectrum than a clearcut distinction. Even ML and Pascal have ways to circumvent the type system, and even C is typesafe unless you use unsafe constructs. IOW from a type-theoretic point of view, there is no real difference between their typesafe and not typesafe languages in the statically typed column; the difference is in the amount of unsafe construct usage in practial programs. It's also relevant how straightforward it is to distinguish between safe and unsafe code, how explicit you have to be when you use unsafe code, how likely it is that you accidentally use unsafe code without being aware of it, what the generally accepted conventions in a language community are, etc. pp. Fully agreed. -- http://mail.python.org/mailman/listinfo/python-list
Re: What is Expressiveness in a Computer Language
[EMAIL PROTECTED] wrote: In this context, the term latently-typed language refers to the language that a programmer experiences, not to the subset of that language which is all that we're typically able to formally define. That language is not a subset, if at all, it's the other way round, but I'd say they are rather incomparable. That is, they are different languages. The subset characterization is not important for what I'm saying. The fact that they are different languages is what's important. If you agree about that, then you can at least understand which language I'm referring to when I say latently-typed language. Besides, many dynamically-typed languages have no formal models, in which case the untyped formal model I've referred to is just a speculative construct. The language I'm referring to with latently-typed language is the language that programmers are familiar with, and work with. That is starting to get a bit too mystical for my tastes. I have to agree. \sarcasm One step further, and somebody starts calling C a latently memory-safe language, because a real programmer knows that his code is in a safe subset... And where he is wrong, dynamic memory page protection checks will guide him. That's a pretty apt comparison, and it probably explains how it is that the software we all use, which relies so heavily on C, works as well as it does. But the comparison critiques the practice of operating without static guarantees, it's not a critique of the terminology. Anton -- http://mail.python.org/mailman/listinfo/python-list
Re: What is Expressiveness in a Computer Language
Joachim Durchholz [EMAIL PROTECTED] wrote: The immutability comes from the fact (perhaps implicit in these textbooks, or perhaps they are not really texts on formal type theory) that types are assigned to expressions, That doesn't *define* what's a type or what isn't! I'm sorry if you don't like it, but that's all there is. That's the point that's being missed here. It's not as if there's this thing called a type, and then we can consider how it is used by formal type systems. A type, in formal type theory, is ANY label that is assigned to expressions of a program for the purpose of making a formal type system work. If you wish to claim a different use of the word and then try to define what is or is not a type, then be my guest. However, formal type theory will still not adopt whatever restrictions you come up with, and will continue to use the word type as the field has been using the word for a good part of a century now. The first step toward considering the similarities and differences between the different uses of type in dynamic type systems and formal type theory is to avoid confusing aspects of one field with the other. -- Chris Smith - Lead Software Developer / Technical Trainer MindIQ Corporation -- http://mail.python.org/mailman/listinfo/python-list
Re: What is Expressiveness in a Computer Language
Joachim Durchholz wrote: Chris Smith schrieb: Joachim Durchholz [EMAIL PROTECTED] wrote: Sorry, I have to insist that it's not me who's stretching terms here. All textbook definitions that I have seen define a type as the set/operations/axioms triple I mentioned above. No mention of immutability, at least not in the definitions. The immutability comes from the fact (perhaps implicit in these textbooks, or perhaps they are not really texts on formal type theory) that types are assigned to expressions, That doesn't *define* what's a type or what isn't! If it's impossible to assign types to all expressions of a program in a language, that does mean that there's no useful type theory for the program, but it most definitely does not mean that there are no types in the program. I can still sensibly talk about sets of values, sets of allowable operations over each value, and about relationships between inputs and outputs of these operations. So programs have types, even if they don't have a static type system. Q.E.D. Of course not. Otherwise programs using dynamically typed systems wouldnt exist. Regards, Jo I haven't read all of this thread, I wonder, is the problem to do with Class being mistaken for Type? (which is usually the issue) -- http://mail.python.org/mailman/listinfo/python-list
Re: What is Expressiveness in a Computer Language
Chris F Clark wrote: Chris F Clark (I) wrote: I'm particularly interested if something unsound (and perhaps ambiguous) could be called a type system. I definitely consider such things type systems. Marshall [EMAIL PROTECTED] wrote: I don't understand. You are saying you prefer to investigate the unsound over the sound? ... Again, I cannot understand this. In a technical realm, vagueness is the opposite of understanding. At the risk of injecting too much irrelevant philosophy into the discussion, I will with great trepdiation reply. I agree this is OT, but I'm not sure about the source of trepidation. First in the abstrtact: No, understanding is approximating. Agreed. The world is inherently vague. Our understanding of the world is vague. The world itself is not at all vague. We make false symbolic models of the world which are consistent, but at some level they do not reflect reality, Yes... because reality isn't consistent. What?! Only by abtracting away the inherent infinite amout of subtlety present in the real universe can we come to comprehensible models. Sure. (Although I object to infinite.) Those models can be consistent, but they are not the universe. The models in their consistency, prove things which are not true about the real universe. Sure, sure, sure. None of these is a reaon to prefer the unsound over the sound. Now in the concrete: In my work productivity is ultimately important. Therefore, we live by the 80-20 rule in numerous variations. One of ths things we do to achieve productivity is simplify things. In fact, we are more interested in an unsound simplification that is right 80% of the time, but takes only 20% of the effort to compute, than a completely sound (100% right) model which takes 100% of the time to compute (which is 5 times as long). We are playing the probabilities. What you are describing is using a precise mathematical function to approximate a different precise mathematical function. This argues for the value of approximation functions, which I do not dispute. But this does not in any way support the idea of vague trumping precise, informal trumping formal, or unsoundness as an end in itself. It's not that we don't respect the sound underpining, the model which is consistent and establishes certain truths. However, what we want is the rule of thumb which is far simpler and approximates the sound model with reasonable accuracy. In particular, we accept two types of unsoundness in the model. One, we accept a model which gives wrong answers which are detectable. We code tests to catch those cases, and use a different model to get the right answer. Two, we accept a model which gets the right answer only when over-provisioned. for example, if we know a loop will occassionaly not converge in the n-steps that it theoretically should, we will run the loop for n+m steps until the approximation also converges--even if that requires allocating m extra copies of some small element than are theoretically necessary. A small waste of a small resource, is ok if it saves a waste of a more critical resource--the most critical resource of all being our project timeliness. Υes, I'm quite familiar with modelling, abstraction, approximation, etc. However nothing about those endevours suggests to me that unsoundness is any kind of goal. Marshall's last point: I flipped a coin to see who would win the election; it came up Bush. Therefore I *knew* who was going to win the election before it happened. See the probem? Flipping one coin to determine an election is not playing the probabilities correctly. You need a plausible explanation for why the coin should predict the right answer and a track record of it being correct. If you had a coin that had correctly predicted the previous 42 presidencies and you had an explanation why the coin was right, then it would be credible and I would be willing to wager that it could also predict that the coin could tell us who the 44th president would be. One flip and no explanation is not sufficient. (And to the abstract point, to me that is all knowledge is, some convincing amount of examples and a plausible explanation--anyone who thinks they have more is appealing to a knowledge of the universe that I don't accept.) I used a coin toss; I could also have used a psycic hotline. There is an explanation for why those things work, but the explanation is unsound. Look at where that got Russell and Whitehead. Universal acclaim, such that their names will be praised for centuries to come? I'm just trying to be honest about that fact and find ways to compensate for my own failures. Limitation != failure. Marshal -- http://mail.python.org/mailman/listinfo/python-list
What technologies should I use for my application manager?
Hello! I've just finished working on my first Python app (a Tkinter-based program that displays the content of our application log files in graphical format). It was a great experience that's had a very positive response from my colleagues. So I'd like to try something different for my second Python application. It's a simple server that can launch and monitor the state of our program, to help our software developers. In my mind I have a vision of: * a web server * allows the user to launch our product (choosing from a set of different launch scripts) * allow user to stop a launched product * report state by retrieving data from the RDBMS against which the product runs (Oracle or SQL Server) There seem to be a lot of web server related Python libraries around, and I've no experience in web servers at all. So I'd really appreciate some advice on what Python technologies you think I should base my application on. Thank you in advance! John -- http://mail.python.org/mailman/listinfo/python-list
