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• Good real-world uses of metaclasses (e.g. in Python)

  - by Carles Barrobés

  I'm learning about metaclasses in Python. I think it is a very powerful technique, and I'm looking for good uses for them. I'd like some feedback of good useful real-world examples of using metaclasses. I'm not looking for example code on how to write a metaclass (there are plenty examples of useless metaclasses out there), but real examples where you have applied the technique and it was really the appropriate solution. The rule is: no theoretical possibilities, but metaclasses at work in a real application. I'll start with the one example I know: Django models, for declarative programming, where the base class Model uses a metaclass to fill the model objects of useful ORM functionality from the attribute definitions. Looking forward to your contributions.

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• Drawing unfilled rectangle shape in c++ openGL

  - by Bahaa

  I want to draw unfilled rectangle shape in openGL using c++ programming language but when I used the glBegin(GL_QUADS) or glBegin(GL_POLYGON), the resulted shape is filled but I want to be unfilled. How I can draw unfilled rectangle. void draweRect(void) { glClear(GL_COLOR_BUFFER_BIT); glColor3f(0.0,0.0,1.0); glLineWidth(30); glBegin(GL_POLYGON); glVertex2i(50,90); glVertex2i(100,90); glVertex2i(100,150); glVertex2i(50,150); glEnd(); glFlush(); }

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• How can I declare a pointer structure using {}?

  - by Y_Y

  This probably is one of the easiest question ever in C programming language... I have the following code: typedef struct node { int data; struct node * after; struct node * before; }node; struct node head = {10,&head,&head}; Is there a way I can make head to be *head [make it a pointer] and still have the availability to use '{ }' [{10,&head,&head}] to declare an instance of head and still leave it out in the global scope? For example: //not legal!!! struct node *head = {10,&head,&head};

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• How compiling circular dependencies works?

  - by Fabio F.

  I've made the example in Java but I think (not tested) that it works in other (all?) languages. You have 2 files M.java that says public class MType{ XType x; MType(){ x = null;} } and another file XType.java (in the same directory) public class XType{ MType m; public XType(MType m){ this.m=m;} } Ok it's BAD programming , but.. if you run javac XType it compiles: compiles even MTypes because XType needs it. But.. MType needs XType.. how it works? How does the compiler know what is happening? Probably is a stupid question, but I would like to know how the compiler (javac or other compilers if you know.) manages that situation, not how to avoid it. I'm asking because i'm writing a precompiler and I would like to manage that situation.. Thank you

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• What is an instance of a field called?

  - by waxwing

  This might be an odd question, but it has actually caused me some headache. In Object oriented programming, there are accepted names for key concepts. In our model, we have classes with methods and fields. Now, going to the data world: An instance of a class is called an object. An instance of a field is called... what? A value? Isn't the term value a little broad for this? I have been offered "property" as well, but isn't property also part of the model and not the data? (This is not purely academic, I am actually coding these concepts.)

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• C++ code generation for repeted task

  - by sateesh

  Hi, I have something like below which will get repeated many times based on the function that get called for e.g acceptfunction() { inserter["quantity"] = sdd.getfloat(quantity); inserter["prodtype"] = sdd.getstring(prodtype); : : so on } Like accept above there are 20 more functions(reject,cancel etc) which will do the similar thing.But the parameteres they insert can differ based on function called. How can I automate this kind of code.So that I dont need to write new function from scratch.Basically what I need is if i provide parametres like ("quantity",prodtype) through some text file or xml, it should generate the required function with the input parametres. Is this task can be handled through C++ tempalte Meta programming or someother code generation tool will help me to do this?

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• How can I get the domain name for a user logged into a Mac via Active Directory

  - by Lawrence Johnston

  In my Cocoa app how can I get the current user's domain when they're logged in via Active Directory? I need to determine two things: 1. If the current user is logged on to an Active Directory domain (only need to handle Active Directory). 2. If 1, the domain of the user. I've found references to Directory Services and the Open Directory Programming Guide but the latter is 10.6 only (I must support 10.5+) and I could not find any examples for the former that gave me an idea of what I needed to do.

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• python: find and replace numbers < 1 in text file

  - by hjp

  I'm pretty new to Python programming and would appreciate some help to a problem I have... Basically I have multiple text files which contain velocity values as such: 0.259515E+03 0.235095E+03 0.208262E+03 0.230223E+03 0.267333E+03 0.217889E+03 0.156233E+03 0.144876E+03 0.136187E+03 0.137865E+00 etc for many lines... What I need to do is convert all the values in the text file that are less than 1 (e.g. 0.137865E+00 above) to an arbitrary value of 0.100000E+01. While it seems pretty simple to replace specific values with the 'replace()' method and a while loop, how do you do this if you want to replace a range? thanks

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• Printing python tkinter output

  - by Eric

  I am trying to print the contents of a python tkinter canvas. I have tried using the postscript method of canvas to create a postscript file, but I get a blank page. I know this is because I have embedded widgets, and these do not get rendered by the postscript method. Before I rewrite my program to create a more printer-friendly layout, can someone suggest a way to approach this problem? All of the programming books I have ever read approach the problem of sending output to a printer with a bit of hand-waving, something along the lines of: "It's a difficult problem that depends on interacting with the operating system." I also have a hard time finding resources about this because of all the pages related to printing to the screen. I am using Python 2.6, on Ubuntu 9.04.

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• Consolidating separate Loan, Purchase & Sales tables into one transaction table.

  - by Frank Computer

  INFORMIX-SE with ISQL 7.3: I have separate tables for Loan, Purchase & Sales transactions. Each tables rows are joined to their respective customer rows by: customer.id [serial] = loan.foreign_id [integer]; = purchase.foreign_id [integer]; = sale.foreign_id [integer]; I would like to consolidate the three tables into one table called "transaction", where a column "transaction.trx_type" [char(1)] {L=Loan, P=Purchase, S=Sale} identifies the transaction type. Is this a good idea or is it better to keep them in separate tables? Storage space is not a concern, I think it would be easier programming & user=wise to have all types of transactions under one table.

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• Writing an OS for Motorola 68K processor. Can I emulate it? And can I test-drive OS development?

  - by ulver

  Next term, I'll need to write a basic operating system for Motorola 68K processor as part of a course lab material. Is there a Linux emulator of a basic hardware setup with that processor? So my partners and I can debug quicker on our computers instead of physically restarting the board and stuff. Is it possible to apply test-driven development technique to OS development? Code will be mostly assembly and C. What will be the main difficulties with trying to test-drive this? Any advice on how to do it?

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• Is there a server side API for Team Foundaion Server

  - by Ralph Shillington

  It would seem there is precious little documentation on programming against a TFS 2010 instance. What bits I have found, have next to nothing in the case of documentation beyond barebones listing of client access classes and their members, most likely autogenerated from the code comments. As I'm interested in building a silverlight client against TFS, I will need access to server side API (ideally the silverlight app will talk to my server (mainly for work items) and my server will in turn talk to the TFS server for the goods. Where is the doumentation (if any) for this kind of TFS integration?

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• Crossplatform development for iPhone & Android

  - by LeonixSolutions

  As far as I can see there doesn't seem to any mature environment for crossplatform development for iPhone & Android slate (but feel free to correct me). I don't know Ipad, I must admit. Any reason why plain Java wouldn't cut it? (maybe underlying things like database (I am not too concerned with hardware)) I am thinking to try to make everything browser based, although that won't get around the d/b & h/w issues, unless there is JS framework that does so. Any advice?

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• Are `return` and `break` useless inside a Ruby block when used as a callback?

  - by Skilldrick

  In Rails, blocks can be used as callbacks, e.g.: class User < ActiveRecord::Base validates_presence_of :login, :email before_create {|user| user.name = user.login.capitalize if user.name.blank?} end When a block is used like this, is there any use for break and return? I'm asking because normally in a block, break will break out of the loop, and return will return from the enclosing method. But in a callback context, I can't get my head round what that means. The Ruby Programming Language suggests that return could cause a LocalJumpError but I haven't been able to reproduce this in a Rails callback. Edit: with the following code I'd expect a LocalJumpError, but all the return does is stop the rest of the callback executing. class User < ActiveRecord::Base validates_presence_of :login, :email before_create do |user| return user.name = user.login.capitalize end

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• Magento quantity field doesn't work

  - by madmax

  Hi, i simply can't find a solution to my problem! The quantity field worked as it should. After a few months of programming on the whole shop, i wanted to test the quantity field and recognized that it doesn't function. I only can add one product to the cart although i typed “3” in the quantity field. I didn’t change anything in product/view.phtml and addtocart.phtml. Don't know where i have to search for this error. Maybe someone can give me a tip... greets max

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• Is It Worth Using Bitwise Operators In Methods?

  - by user1626141

  I am very new to Java (and programming in general, my previous experience is with ActionScript 2.0 and some simple JavaScript), and I am working my way slowly and methodically through Java: A Beginner's Guide by Herbert Schildt. It is an incredible book. For one thing, I finally understand more-or-less what bitwise operators (which I first encountered in ActionScript 2.0) do, and that they are more efficient than other methods for certain sums. My question is, is it more efficient to use a method that uses, say, a shift right, to perform all your divisions/2 (or divisions/even) for you in a large program with many calculations (in this case, a sprawling RPG), or is it more efficient to simply use standard mathematical operations because the compiler will optimise it all for you? Or, am I asking the wrong question entirely?

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• Django: common template subsections

  - by Parand

  What's a good way to handle commonly occurring subsections of templates? For example, there is a sub-header section that's used across 4 different pages. The pages are different enough to not work well with template inheritance (ie. "extends" doesn't fit well). Is "include" the recommended method here? It feels a bit heavyweight, requiring each subsection or snippet to be in its own file. Are there any performance issues in using include or is it smart about forming template from the subsections (ie. if I make extensive use of it, do I pay any penalties)? I think what I'm looking for is something like template tags, but without the programming - a simple way to create a library of html template tags I can sprinkle in other templates.

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• How does lock(syncRoot) make sense on a static method?

  - by Rising Star

  The following code is excerpted from the (Windows Identity Foundation SDK) template that MS uses to create a new Security Token Service Web Site. public static CustomSecurityTokenServiceConfiguration Current { get { HttpApplicationState httpAppState = HttpContext.Current.Application; CustomSecurityTokenServiceConfiguration customConfiguration = httpAppState.Get( CustomSecurityTokenServiceConfigurationKey ) as CustomSecurityTokenServiceConfiguration; if ( customConfiguration == null ) { lock ( syncRoot ) { customConfiguration = httpAppState.Get( CustomSecurityTokenServiceConfigurationKey ) as CustomSecurityTokenServiceConfiguration; if ( customConfiguration == null ) { customConfiguration = new CustomSecurityTokenServiceConfiguration(); httpAppState.Add( CustomSecurityTokenServiceConfigurationKey, customConfiguration ); } } } return customConfiguration; } } I'm relatively new to multi-threaded programming. I assume that the reason for the lock statement is to make this code thread-safe in the event that two web requests arrive at the web site at the same time. However, I would have thought that using lock (syncRoot) would not make sense because syncRoot refers to the current instance that this method is operating on... but this is a static method? How does this make sense?

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• Sharepoint Web performance optimization

  - by hertzel

  We are running on SSL on following server topology: 1 ISA (SSL Terminate/cache/proxy+AD authentication) 1 Sharepoint 1 IBM DB2 Database as enterprise/corporate DB 1 MS SQL Server as local DB We have recently optimized the caching, compression, minification, and other ASP.net best practices such as viewstate and cookie sizes, minimizing round trips, parallel connections/domain sharding and a lot more.... Now we are not convinced that the we are in an optimized position as the network resources i.e. bandwidth and especially latency are out of our control!! The client/browser to server/sharepoint is trans-Atlantic i.e. (ASIA, USA, EUROPE). As of my understanding the only ways to improve the network (latency) are: - TCP/SSL optimization - hardware/software? - CDNs - cloud or our own ? Your opinion and insights would be much appreciated Best regards Hertzel

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• Aside from performance concerns, is Java still chosen over Groovy/JRuby etc.?

  - by yar

  [This is an empirical question about the state-of-the-art: I am NOT asking if Java is cooler or less cool than the dynamic languages that work in the JVM.] Aside from cases where performance is a main decision factor, do companies/developers still willingly chose Java over Groovy, JRuby or JPython? Personal Note: The reason I am asking is that, while I do some subset of my professional work in Ruby (not JRuby, for now), in my personal projects I use Java. While I have written non-trivial apps in Groovy, I prefer Java, but I wonder if I should just get over it and do everything in Groovy. I like Java because I feel that static typing saves me time and aids refactoring. (No, I am not familiar with Scala.) However, I feel that this very empirical, on-topic programming question may inform my decision.

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• Need help with some C# Counting Code

  - by kaywai

  Hi, I'm trying to code a counter in Ninjatrader which uses C# as its programming language. I would like this counter to commence counting upon the completion of the first counter and once it commences counting to consider only the new condition when counting. So, the first counter commences when Close[0] < Close[4]. The second counter commences ONLY after the first counter has reached 9 and its condition for counting is Close[0] <= Low[2]. I don't know how to write the part of the code where the second counter commences counting and its counts are independent of the first counter reaching 9.

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• What are the difference between Cygwin on windows and real UNIX environment

  - by Tarun

  Hi, I am a C/C++ developer. I have never done C++ programming on UNIX, I have done only on windows. I want to practice C++ on Unix. (Because all big companies ask C++ with Unix). I have a laptop on which i do not want to install any other OS (because i have installed very important software on it and i don't have setups) So, I searched and found CygWin which is Unix emulator for Windows. I am thinking to practice C++ on this. Please help me, how can I practice/learn in more close to the environment(Unix Environment) that is used in Big companies like IBM. What will be the difference between Unix and Cygwin?

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• how to select specific number of child entities instead of all in entity framework 3.5?

  - by Sasha

  Hi all, i am wondering how can i select specific number of child objects instead of taking them all with include? lets say i have object 'Group' and i need to select last ten students that joined the group. When i use '.Include("Students"), EF includes all students. I was trying to use Take(10), but i am pretty new to EF and programming as well, so i couldn't figure it out. Any suggestions? UPDATED: ok, i have Group object already retrieved from db like this: Group group = db.Groups.FirstOrDefault(x=>x.GroupId == id) I know that i can add Include("Students") statement, but that would bring ALL students, and their number could be quite big whether i need only freshest 10 students. Can i do something like this: var groupWithStudents = group.Students.OrderByDescending(//...).Take(10);? The problem with this is that Take< no longer appears in intellisense. Is this clear enough? Thanks for responses

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• Ubuntu Wired network(ethernet does not work)

  - by badnaam

  It was working just fine, until the other day I yanked it out. The wireless works just fine on the same router. If I login to a windows 7 instance on this dual boot laptop then the ehternet works just fine. So it's not a hardware, cable or router issue. The card even gets an ip, but I can't connect to the internet. Here are the details from route, iptables, ifconfig, ping etc. Any ideas? I have been struggling with this for day, none seems to have an answer. http://pastie.org/954816

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• Access static constant variable from multiple threads in C

  - by user325519

  I have some experience with multithread programming under Linux (C/C++ & POSIX threads), however most obvious cases are sometimes very complicated. I have several static constant variables (global and function local) in my code, can I access them simultaneously from multiple threads without using mutexes? Because I don't modify them it should be ok, but it's always better to ask. I have to do heavy speed optimization, so even as fast operations as mutex lock/unlock are quite expensive for me, especially because my application is going to access these variables form long loops.

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