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• Python - How can I make this code asynchronous?

  - by dave

  Here's some code that illustrates my problem: def blocking1(): while True: yield 'first blocking function example' def blocking2(): while True: yield 'second blocking function example' for i in blocking1(): print 'this will be shown' for i in blocking2(): print 'this will not be shown' I have two functions which contain while True loops. These will yield data which I will then log somewhere (most likely, to an sqlite database). I've been playing around with threading and have gotten it working. However, I don't really like it... What I would like to do is make my blocking functions asynchronous. Something like: def blocking1(callback): while True: callback('first blocking function example') def blocking2(callback): while True: callback('second blocking function example') def log(data): print data blocking1(log) blocking2(log) How can I achieve this in Python? I've seen the standard library comes with asyncore and the big name in this game is Twisted but both of these seem to be used for socket IO. How can I async my non-socket related, blocking functions?

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• How to get better at solving Dynamic programming problems

  - by newbie

  I recently came across this question: "You are given a boolean expression consisting of a string of the symbols 'true', 'false', 'and', 'or', and 'xor'. Count the number of ways to parenthesize the expression such that it will evaluate to true. For example, there is only 1 way to parenthesize 'true and false xor true' such that it evaluates to true." I knew it is a dynamic programming problem so i tried to come up with a solution on my own which is as follows. Suppose we have a expression as A.B.C.....D where '.' represents any of the operations and, or, xor and the capital letters represent true or false. Lets say the number of ways for this expression of size K to produce a true is N. when a new boolean value E is added to this expression there are 2 ways to parenthesize this new expression 1. ((A.B.C.....D).E) ie. with all possible parenthesizations of A.B.C.....D we add E at the end. 2. (A.B.C.(D.E)) ie. evaluate D.E first and then find the number of ways this expression of size K can produce true. suppose T[K] is the number of ways the expression with size K produces true then T[k]=val1+val2+val3 where val1,val2,val3 are calculated as follows. 1)when E is grouped with D. i)It does not change the value of D ii)it inverses the value of D in the first case val1=T[K]=N.( As this reduces to the initial A.B.C....D expression ). In the second case re-evaluate dp[K] with value of D reversed and that is val1. 2)when E is grouped with the whole expression. //val2 contains the number of 'true' E will produce with expressions which gave 'true' among all parenthesized instances of A.B.C.......D i) if true.E = true then val2 = N ii) if true.E = false then val2 = 0 //val3 contains the number of 'true' E will produce with expressions which gave 'false' among all parenthesized instances of A.B.C.......D iii) if false.E=true then val3=( 2^(K-2) - N ) = M ie. number of ways the expression with size K produces a false [ 2^(K-2) is the number of ways to parenthesize an expression of size K ]. iv) if false.E=false then val3 = 0 This is the basic idea i had in mind but when i checked for its solution http://people.csail.mit.edu/bdean/6.046/dp/dp_9.swf the approach there was completely different. Can someone tell me what am I doing wrong and how can i get better at solving DP so that I can come up with solutions like the one given above myself. Thanks in advance.

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• Learning by doing (and programming by trial and error)

  - by AlexBottoni

  How do you learn a new platform/toolkit while producing working code and keeping your codebase clean? When I know what I can do with the underlying platform and toolkit, I usually do this: I create a new branch (with GIT, in my case) I write a few unit tests (with JUnit, for example) I write my code until it passes my tests So far, so good. The problem is that very often I do not know what I can do with the toolkit because it is brand new to me. I work as a consulant so I cannot have my preferred language/platform/toolkit. I have to cope with whatever the customer uses for the task at hand. Most often, I have to deal (often in a hurry) with a large toolkit that I know very little so I'm forced to "learn by doing" (actually, programming by "trial and error") and this makes me anxious. Please note that, at some point in the learning process, usually I already have: read one or more five-stars books followed one or more web tutorials (writing working code a line at a time) created a couple of small experimental projects with my IDE (IntelliJ IDEA, at the moment. I use Eclipse, Netbeans and others, as well.) Despite all my efforts, at this point usually I can just have a coarse understanding of the platform/toolkit I have to use. I cannot yet grasp each and every detail. This means that each and every new feature that involves some data preparation and some non-trivial algorithm is a pain to implement and requires a lot of trial-and-error. Unfortunately, working by trial-and-error is neither safe nor easy. Actually, this is the phase that makes me most anxious: experimenting with a new toolkit while producing working code and keeping my codebase clean. Usually, at this stage I cannot use the Eclipse Scrapbook because the code I have to write is already too large and complex for this small tool. In the same way, I cannot use any more an indipendent small project for my experiments because I need to try the new code in place. I can just write my code in place and rely on GIT for a safe bail-out. This makes me anxious because this kind of intertwined, half-ripe code can rapidly become incredibly hard to manage. How do you face this phase of the development process? How do you learn-by-doing without making a mess of your codebase? Any tips&tricks, best practice or something like that?

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• HTML5 game programming style

  - by fnx

  I am currently trying learn javascript in form of HTML5 games. Stuff that I've done so far isn't too fancy since I'm still a beginner. My biggest concern so far has been that I don't really know what is the best way to code since I don't know the pros and cons of different methods, nor I've found any good explanations about them. So far I've been using the worst (and propably easiest) method of all (I think) since I'm just starting out, for example like this: var canvas = document.getElementById("canvas"); var ctx = canvas.getContext("2d"); var width = 640; var height = 480; var player = new Player("pic.png", 100, 100, ...); also some other global vars... function Player(imgSrc, x, y, ...) { this.sprite = new Image(); this.sprite.src = imgSrc; this.x = x; this.y = y; ... } Player.prototype.update = function() { // blah blah... } Player.prototype.draw = function() { // yada yada... } function GameLoop() { player.update(); player.draw(); setTimeout(GameLoop, 1000/60); } However, I've seen a few examples on the internet that look interesting, but I don't know how to properly code in these styles, nor do I know if there are names for them. These might not be the best examples but hopefully you'll get the point: 1: Game = { variables: { width: 640, height: 480, stuff: value }, init: function(args) { // some stuff here }, update: function(args) { // some stuff here }, draw: function(args) { // some stuff here }, }; // from http://codeincomplete.com/posts/2011/5/14/javascript_pong/ 2: function Game() { this.Initialize = function () { } this.LoadContent = function () { this.GameLoop = setInterval(this.RunGameLoop, this.DrawInterval); } this.RunGameLoop = function (game) { this.Update(); this.Draw(); } this.Update = function () { // update } this.Draw = function () { // draw game frame } } // from http://www.felinesoft.com/blog/index.php/2010/09/accelerated-game-programming-with-html5-and-canvas/ 3: var engine = {}; engine.canvas = document.getElementById('canvas'); engine.ctx = engine.canvas.getContext('2d'); engine.map = {}; engine.map.draw = function() { // draw map } engine.player = {}; engine.player.draw = function() { // draw player } // from http://that-guy.net/articles/ So I guess my questions are: Which is most CPU efficient, is there any difference between these styles at runtime? Which one allows for easy expandability? Which one is the most safe, or at least harder to hack? Are there any good websites where stuff like this is explained? or... Does it all come to just personal preferance? :)

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• Multiple asynchronous method calls to method while in a loop

  - by ranabra

  I have spent a whole day trying various ways using 'AddOnPreRenderCompleteAsync' and 'RegisterAsyncTask' but no success so far. I succeeded making the call to the DB asynchronous using 'BeginExecuteReader' and 'EndExecuteReader' but that is missing the point. The asynch handling should not be the call to the DB which in my case is fast, it should be afterwards, during the 'while' loop, while calling an external web-service. I think the simplified pseudo code will explain best: (Note: the connection string is using 'MultipleActiveResultSets') "Select ID, UserName from MyTable" 'Open connection to DB ExecuteReader(); if (DR.HasRows) {     while (DR.Read())     {         'Call external web-service         'and get current Temperature of each UserName - DR["UserName"].ToString()         'Update my local DB         Update MyTable set Temperature = ValueFromWebService where UserName =                                       DR["UserName"]         CmdUpdate.ExecuteNonQuery();     }     'Close connection etc } Accessing the DB is fast. Getting the returned result from the external web-service is slow and that at least should be handled Asynchnously. If each call to the web service takes just 1 second, assuming I have only 100 users it will take minimum 100 seconds for the DB update to complete, which obviously is not an option. There eventually should be thousands of users (currently only 2). Currently everything works, just very synchnously :) Thoughts to myself: Maybe my way of approaching this is wrong? Maybe the entire process should be called Asynchnously Many thanx

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• Dealing with asynchronous control structures (Fluent Interface?)

  - by Christophe Herreman

  The initialization code of our Flex application is doing a series of asynchronous calls to check user credentials, load external data, connecting to a JMS topic, etc. Depending on the context the application runs in, some of these calls are not executed or executed with different parameters. Since all of these calls happen asynchronously, the code controlling them is hard to read, understand, maintain and test. For each call, we need to have some callback mechanism in which we decide what call to execute next. I was wondering if anyone had experimented with wrapping these calls in executable units and having a Fluent Interface (FI) that would connect and control them. From the top of my head, the code might look something like: var asyncChain:AsyncChain = execute(LoadSystemSettings) .execute(LoadAppContext) .if(IsAutologin) .execute(AutoLogin) .else() .execute(ShowLoginScreen) .etc; asyncChain.execute(); The AsyncChain would be an execution tree, build with the FI (and we could of course also build one without a FI). This might be an interesting idea for environments that run in a single threaded model like the Flash Player, Silverlight, JavaFX?, ... Before I dive into the code to try things out, I was hoping to get some feedback.

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• Asynchronous background processes in Python?

  - by Geuis

  I have been using this as a reference, but not able to accomplish exactly what I need: http://stackoverflow.com/questions/89228/how-to-call-external-command-in-python/92395#92395 I also was reading this: http://www.python.org/dev/peps/pep-3145/ For our project, we have 5 svn checkouts that need to update before we can deploy our application. In my dev environment, where speedy deployments are a bit more important for productivity than a production deployment, I have been working on speeding up the process. I have a bash script that has been working decently but has some limitations. I fire up multiple 'svn updates' with the following bash command: (svn update /repo1) & (svn update /repo2) & (svn update /repo3) & These all run in parallel and it works pretty well. I also use this pattern in the rest of the build script for firing off each ant build, then moving the wars to Tomcat. However, I have no control over stopping deployment if one of the updates or a build fails. I'm re-writing my bash script with Python so I have more control over branches and the deployment process. I am using subprocess.call() to fire off the 'svn update /repo' commands, but each one is acting sequentially. I try '(svn update /repo) &' and those all fire off, but the result code returns immediately. So I have no way to determine if a particular command fails or not in the asynchronous mode. import subprocess subprocess.call( 'svn update /repo1', shell=True ) subprocess.call( 'svn update /repo2', shell=True ) subprocess.call( 'svn update /repo3', shell=True ) I'd love to find a way to have Python fire off each Unix command, and if any of the calls fails at any time the entire script stops.

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• Asynchronous event loop design and issues.

  - by Artyom

  Hello, I'm designing event loop for asynchronous socket IO using epoll/devpoll/kqueue/poll/select (including windows-select). I have two options of performing, IO operation: Non-blocking mode, poll on EAGAIN Set socket to non-blocking mode. Read/Write to socket. If operation succeeds, post completion notification to event loop. If I get EAGAIN, add socket to "select list" and poll socket. Polling mode: poll and then execute Add socket to select list and poll it. Wait for notification that it is readable writable read/write Post completion notification to event loop of sucseeds To me it looks like first would require less system calls when using in normal mode, especially for writing to socket (buffers are quite big). Also it looks like that it would be possible to reduce the overhead over number of "select" executions, especially it is nice when you do not have something that scales well as epoll/devpoll/kqueue. Questions: Are there any advantages of the second approach? Are there any portability issues with non-blocking operations on sockets/file descriptors over numerous operating systems: Linux, FreeBSD, Solaris, MacOSX, Windows. Notes: Please do not suggest using existing event-loop/socket-api implementations

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• Blackberry Asynchronous HTTP Requests - How?

  - by Kai

  The app I'm working on has a self contained database. The only time I need HTTP request is when the user first loads the app. I do this by calling a class that verifies whether or not a local DB exists and, if not, create one with the following request: HttpRequest data = new HttpRequest("http://www.somedomain.com/xml", "GET", this); data.start(); This xml returns a list of content, all of which have images that I want to fetch AFTER the original request is complete and stored. So something like this won't work: HttpRequest data = new HttpRequest("http://www.somedomain.com/xml", "GET", this); data.start(); HttpRequest images = new HttpRequest("http://www.somedomain.com/xmlImages", "GET", this); images.start(); Since it will not treat this like an asynchronous request. I have not found much information on adding callbacks to httpRequest, or any other method I could use to ensure operation 2 does not execute until operation 1 is complete. Any help would be appreciated. Thanks

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• Sequential access to asynchronous sockets

  - by Lars A. Brekken

  I have a server that has several clients C1...Cn to each of which there is a TCP connection established. There are less than 10,000 clients. The message protocol is request/response based, where the server sends a request to a client and then the client sends a response. The server has several threads, T1...Tm, and each of these may send requests to any of the clients. I want to make sure that only one of these threads can send a request to a specific client at any one time, while the other threads wanting to send a request to the same client will have to wait. I do not want to block threads from sending requests to different clients at the same time. E.g. If T1 is sending a request to C3, another thread T2 should not be able to send anything to C3 until T1 has received its response. I was thinking of using a simple lock statement on the socket: lock (c3Socket) { // Send request to C3 // Get response from C3 } I am using asynchronous sockets, so I may have to use Monitor instead: Monitor.Enter(c3Socket); // Before calling .BeginReceive() And Monitor.Exit(c3Socket); // In .EndReceive I am worried about stuff going wrong and not letting go of the monitor and therefore blocking all access to a client. I'm thinking that my heartbeat thread could use Monitor.TryEnter() with a timeout and throw out sockets that it cannot get the monitor for. Would it make sense for me to make the Begin and End calls synchronous in order to be able to use the lock() statement? I know that I would be sacrificing concurrency for simplicity in this case, but it may be worth it. Am I overlooking anything here? Any input appreciated.

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• how to use q.js promises to work with multiple asynchronous operations

  - by kimsia

  Note: This question is also cross-posted in Q.js mailing list over here. i had a situation with multiple asynchronous operations and the answer I accepted pointed out that using Promises using a library such as q.js would be more beneficial. I am convinced to refactor my code to use Promises but because the code is pretty long, i have trimmed the irrelevant portions and exported the crucial parts into a separate repo. The repo is here and the most important file is this. The requirement is that I want pageSizes to be non-empty after traversing all the dragged'n dropped files. The problem is that the FileAPI operations inside getSizeSettingsFromPage function causes getSizeSettingsFromPage to be async. So I cannot place checkWhenReady(); like this. function traverseFiles() { for (var i=0, l=pages.length; i<l; i++) { getSizeSettingsFromPage(pages[i], calculateRatio); } checkWhenReady(); // this always returns 0. } This works, but it is not ideal. I prefer to call checkWhenReady just ONCE after all the pages have undergone this function calculateRatio successfully. function calculateRatio(width, height, filename) { // .... code pageSizes.add(filename, object); checkWhenReady(); // this works but it is not ideal. I prefer to call this method AFTER all the `pages` have undergone calculateRatio // ..... more code... } How do I refactor the code to make use of Promises in Q.js?

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• Asynchronous callback for network in Objective-C Iphone

  - by vodkhang

  I am working with network request - response in Objective-C. There is something with asynchronous model that I don't understand. In summary, I have a view that will show my statuses from 2 social networks: Twitter and Facebook. When I clicked refresh, it will call a model manager. That model manager will call 2 service helpers to request for latest items. When 2 service helpers receive data, it will pass back to model manager and this model will add all data into a sorted array. What I don't understand here is that : when response from social networks come back, how many threads will handle the response. From my understanding about multithreading and networking (in Java), there must have 2 threads handle 2 responses and those 2 threads will execute the code to add the responses to the array. So, it can have race condition and the program can go wrong right? Is it the correct working model of iphone objective-C? Or they do it in a different way that it will never have race condition and we don't have to care about locking, synchronize? Here is my example code: ModelManager.m - (void)updateMyItems:(NSArray *)items { self.helpers = [self authenticatedHelpersForAction:NCHelperActionGetMyItems]; for (id<NCHelper> helper in self.helpers) { [helper updateMyItems:items]; // NETWORK request here } } - (void)helper:(id <NCHelper>)helper didReturnItems:(NSArray *)items { [self helperDidFinishGettingMyItems:items callback:@selector(model:didGetMyItems:)]; break; } } // some private attributes int *_currentSocialNetworkItemsCount = 0; // to count the number of items of a social network - (void)helperDidFinishGettingMyItems:(NSArray *)items { for (Item *item in items) { _currentSocialNetworkItemsCount ++; } NSLog(@"count: %d", _currentSocialNetworkItemsCount); _currentSocialNetworkItemsCount = 0; } I want to ask if there is a case that the method helperDidFinishGettingMyItems is called concurrently. That means, for example, faceboook returns 10 items, twitter returns 10 items, will the output of count will ever be larger than 10? And if there is only one single thread, how can the thread finishes parsing 1 response and jump to the other response because, IMO, thread is only executed sequently, block of code by block of code

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• STL algorithms and concurrent programming

  - by Andrew

  Hello everyone, Can any of STL algorithms/container operations like std::fill, std::transform be executed in parallel if I enable OpenMP for my compiler? I am working with MSVC 2008 at the moment. Or maybe there are other ways to make it concurrent? Thanks.

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• Asynchronous subprocess on Windows

  - by Stigma

  First of all, the overall problem I am solving is a bit more complicated than I am showing here, so please do not tell me 'use threads with blocking' as it would not solve my actual situation without a fair, FAIR bit of rewriting and refactoring. I have several applications which are not mine to modify, which take data from stdin and poop it out on stdout after doing their magic. My task is to chain several of these programs. Problem is, sometimes they choke, and as such I need to track their progress which is outputted on STDERR. pA = subprocess.Popen(CommandA, shell=False, stdout=subprocess.PIPE, stderr=subprocess.PIPE) # ... some more processes make up the chain, but that is irrelevant to the problem pB = subprocess.Popen(CommandB, shell=False, stdout=subprocess.PIPE, stderr=subprocess.PIPE, stdin=pA.stdout ) Now, reading directly through pA.stdout.readline() and pB.stdout.readline(), or the plain read() functions, is a blocking matter. Since different applications output in different paces and different formats, blocking is not an option. (And as I wrote above, threading is not an option unless at a last, last resort.) pA.communicate() is deadlock safe, but since I need the information live, that is not an option either. Thus google brought me to this asynchronous subprocess snippet on ActiveState. All good at first, until I implement it. Comparing the cmd.exe output of pA.exe | pB.exe, ignoring the fact both output to the same window making for a mess, I see very instantaneous updates. However, I implement the same thing using the above snippet and the read_some() function declared there, and it takes over 10 seconds to notify updates of a single pipe. But when it does, it has updates leading all the way upto 40% progress, for example. Thus I do some more research, and see numerous subjects concerning PeekNamedPipe, anonymous handles, and returning 0 bytes available even though there is information available in the pipe. As the subject has proven quite a bit beyond my expertise to fix or code around, I come to Stack Overflow to look for guidance. :) My platform is W7 64-bit with Python 2.6, the applications are 32-bit in case it matters, and compatibility with Unix is not a concern. I can even deal with a full ctypes or pywin32 solution that subverts subprocess entirely if it is the only solution, as long as I can read from every stderr pipe asynchronously with immediate performance and no deadlocks. :)

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• Languages and Tools for Web programming

  - by Mark Szymanski

  I am wanting to start Web Development and I was wondering what languages I would want to learn and what (if at all possible) free tools I would want to use.

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• Are we in a functional programming fad?

  - by TraumaPony

  I use both functional and imperative languages daily, and it's rather amusing to see the surge of adoption of functional languages from both sides of the fence. It strikes me, however, that it looks rather like a fad. Do you think that it's a fad? I know the reasons for using functional languages at times and imperative languages in others, but do you really think that this trend will continue due to the cliched "many-core" revolution that has been only "18 months from now" since 2004 (sort of like communism's Radiant Future), or do you think that it's only temporary; a fascination of the mainstream developer that will be quickly replaced by the next shiny idea, like Web 3.0 or GPGPU? Note, that I'm not trying to start a flamewar or anything (sorry if it sounds bitter), I'm just curious as to whether people will think functional or functional/imperative languages will become mainstream. Edit: By mainstream, I mean, equal number of programmers to say, Python, Java, C#, etc

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• is this possible in java or any other programming language

  - by drake

  public abstract class Master { public void printForAllMethodsInSubClass() { System.out.println ("Printing before subclass method executes"); } } public class Owner extends Master { public void printSomething () { System.out.println ("This printed from Owner"); } public int returnSomeCals () { return 5+5; } } Without messing with methods of subclass...is it possible to execute printForAllMethodsInSubClass() before the method of a subclass gets executed?

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• Programming Language to manipulate an Access Database

  - by Wayne

  By quote, what is the appropiate language to manipulate an Access database? A Windows user interface to manipulate an existing Access Database. ... and why?

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• Your thoughts on Best Practices for Scientific Computing?

  - by John Smith

  A recent paper by Wilson et al (2014) pointed out 24 Best Practices for scientific programming. It's worth to have a look. I would like to hear opinions about these points from experienced programmers in scientific data analysis. Do you think these advices are helpful and practical? Or are they good only in an ideal world? Wilson G, Aruliah DA, Brown CT, Chue Hong NP, Davis M, Guy RT, Haddock SHD, Huff KD, Mitchell IM, Plumbley MD, Waugh B, White EP, Wilson P (2014) Best Practices for Scientific Computing. PLoS Biol 12:e1001745. http://www.plosbiology.org/article/info%3Adoi%2F10.1371%2Fjournal.pbio.1001745 Box 1. Summary of Best Practices Write programs for people, not computers. (a) A program should not require its readers to hold more than a handful of facts in memory at once. (b) Make names consistent, distinctive, and meaningful. (c) Make code style and formatting consistent. Let the computer do the work. (a) Make the computer repeat tasks. (b) Save recent commands in a file for re-use. (c) Use a build tool to automate workflows. Make incremental changes. (a) Work in small steps with frequent feedback and course correction. (b) Use a version control system. (c) Put everything that has been created manually in version control. Don’t repeat yourself (or others). (a) Every piece of data must have a single authoritative representation in the system. (b) Modularize code rather than copying and pasting. (c) Re-use code instead of rewriting it. Plan for mistakes. (a) Add assertions to programs to check their operation. (b) Use an off-the-shelf unit testing library. (c) Turn bugs into test cases. (d) Use a symbolic debugger. Optimize software only after it works correctly. (a) Use a profiler to identify bottlenecks. (b) Write code in the highest-level language possible. Document design and purpose, not mechanics. (a) Document interfaces and reasons, not implementations. (b) Refactor code in preference to explaining how it works. (c) Embed the documentation for a piece of software in that software. Collaborate. (a) Use pre-merge code reviews. (b) Use pair programming when bringing someone new up to speed and when tackling particularly tricky problems. (c) Use an issue tracking tool. I'm relatively new to serious programming for scientific data analysis. When I tried to write code for pilot analyses of some of my data last year, I encountered tremendous amount of bugs both in my code and data. Bugs and errors had been around me all the time, but this time it was somewhat overwhelming. I managed to crunch the numbers at last, but I thought I couldn't put up with this mess any longer. Some actions must be taken. Without a sophisticated guide like the article above, I started to adopt "defensive style" of programming since then. A book titled "The Art of Readable Code" helped me a lot. I deployed meticulous input validations or assertions for every function, renamed a lot of variables and functions for better readability, and extracted many subroutines as reusable functions. Recently, I introduced Git and SourceTree for version control. At the moment, because my co-workers are much more reluctant about these issues, the collaboration practices (8a,b,c) have not been introduced. Actually, as the authors admitted, because all of these practices take some amount of time and effort to introduce, it may be generally hard to persuade your reluctant collaborators to comply them. I think I'm asking your opinions because I still suffer from many bugs despite all my effort on many of these practices. Bug fix may be, or should be, faster than before, but I couldn't really measure the improvement. Moreover, much of my time has been invested on defence, meaning that I haven't actually done much data analysis (offence) these days. Where is the point I should stop at in terms of productivity? I've already deployed: 1a,b,c, 2a, 3a,b,c, 4b,c, 5a,d, 6a,b, 7a,7b I'm about to have a go at: 5b,c Not yet: 2b,c, 4a, 7c, 8a,b,c (I could not really see the advantage of using GNU make (2c) for my purpose. Could anyone tell me how it helps my work with MATLAB?)

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• What Functional features are worth a little OOP confusion for the benefits they bring?

  - by bonomo

  After learning functional programming in Haskell and F#, the OOP paradigm seems ass-backwards with classes, interfaces, objects. Which aspects of FP can I bring to work that my co-workers can understand? Are any FP styles worth talking to my boss about retraining my team so that we can use them? Possible aspects of FP: Immutability Partial Application and Currying First Class Functions (function pointers / Functional Objects / Strategy Pattern) Lazy Evaluation (and Monads) Pure Functions (no side effects) Expressions (vs. Statements - each line of code produces a value instead of, or in addition to causing side effects) Recursion Pattern Matching Is it a free-for-all where we can do whatever the programming language supports to the limit that language supports it? Or is there a better guideline?

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• Software development magazines [closed]

  - by Sebastian

  Ive spent the last hour or so browsing the web for professional development magazines. I am mostly interested in the java platform, agile methods, "programming in general" (tutorials on languages or whatever, "hot new stuff" etc) and software craftmanship. My best finding yet was pragpub and maybe MSDN magazine. I am willing to pay and have a Zinio account if anyone knows a magazine about programming that is distributed by them. Ive already browsed a couple of related threads here on stackexchange. ACM and IEEE does not seem relevant, as Im not interested in research articles. Maybe conferences like OOPSLA as somebody mentioned in another thread. PS. I prefer if they are in pdf or readable on kindle or a tablet. DS. BR Sebastian

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• Should a new programmer nowadays start with C/C++ or OOP language? [closed]

  - by deviDave

  I've been a programmer for 15+ years. In my time, we all started with C or C++ and then moved to C# or Java. At that time it was a usual practice. Now, my brother wants to follow my steps and I am not sure what advice to give him. So, I am asking the community for an opinion. Should nowadays new programmer with zero programming knowledge start with functional languages (C, C++, etc.) or he should start directly with OOP languages (Java, C#, etc.)? The reply should be considered in the context of my brother's future assignments. He will mainly work on Java mobile applications as well as ASP.NET web apps. He will have to touch with desktop apps, low level programming, drivers, etc. This is the reason I am not sure if he should ever need to learn functional languages.

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• Scheme vs Haskell for an Introduction to Functional Programming?

  - by haziz

  I am comfortable with programming in C and C#, and will explore C++ in the future. I may be interested in exploring functional programming as a different programming paradigm. I am doing this for fun, my job does not involve computer programming, and am somewhat inspired by the use of functional programming, taught fairly early, in computer science courses in college. Lambda calculus is certainly beyond my mathematical abilities, but I think I can handle functional programming. Which of Haskell or Scheme would serve as a good intro to functional programming? I use emacs as my text editor and would like to be able to configure it more easily in the future which would entail learning Emacs Lisp. My understanding, however, is that Emacs Lisp is fairly different from Scheme and is also more procedural as opposed to functional. I would likely be using "The Little Schemer" book, which I have already bought, if I pursue Scheme (seems to me a little weird from my limited leafing through it). Or would use the "Learn You a Haskell for Great Good" if I pursue Haskell. I would also watch the Intro to Haskell videos by Dr Erik Meijer on Channel 9. Any suggestions, feedback or input appreciated. Thanks. P.S. BTW I also have access to F# since I have Visual Studio 2010 which I use for C# development, but I don't think that should be my main criteria for selecting a language.

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• Function-Local Static Const variable Initialization semantics.

  - by Hassan Syed

  The questions are in bold, for those that cannot be bothered reading a question in depth. This is a followup to this question. It is to do with the initialization semantics of static variables in functions. Static variables should be initialized once, and their internal state might be altered later - as I (currently) do in the linked question. However, the code in question does not require the feature to change the state of the variable later. Let me clarrify my position, since I don't require the string object's internal state to change. The code is for a trait class for meta programming, and as such would would benifit from a const char * const ptr -- thus Ideally a local cost static const variable is needed. My educated guess is that in this case the string in question will be optimally placed in memory by the link-loader, and that the code is more secure and maps to the intended semantics. This leads to the semantics of such a variable "The C++ Programming language Third Edition -- Stroustrup" does not have anything (that I could find) to say about this matter. All that is said is that the variable is initialized once when the flow of control of the thread first reaches the code. This leads me to ponder if the following code would be sensible, and if not what are the intended semantics ?. #include <iostream> const char * const GetString(const char * x_in) { static const char * const x = x_in; return x; } int main() { const char * const temp = GetString("yahoo"); std::cout << temp << std::endl; const char * const temp2 = GetString("yahoo2"); std::cout << temp2 << std::endl; } The following compiles on GCC and prints "yahoo" twice. Which is what I want -- However it might not be standards compliant (which is why I post this question). It might be more elegant to have two functions, "SetString" and "String" where the latter forwards to the first. If it is standards compliant does someone know of a templates implementation in boost (or elsewhere) ?

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• Asynchronous Silverlight 4 call to the World of Warcraft armoury streaming XML in C#

  - by user348446

  Hello - I have been stuck on this all weekend and failed miserably! Please help me to claw back my sanity!! Your challenge For my first Silverlight application I thought it would be fun to use the World of Warcraft armoury to list the characters in my guild. This involves making an asyncronous from Silverlight (duh!) to the WoW armoury which is XML based. SIMPLE EH? Take a look at this link and open the source. You'll see what I mean: http://eu.wowarmory.com/guild-info.xml?r=Eonar&n=Gifted and Talented Below is code for getting the XML (the call to ShowGuildies will cope with the returned XML - I have tested this locally and I know it works). I have not managed to get the expected returned XML at all. Notes: If the browser is capable of transforming the XML it will do so, otherwise HTML will be provided. I think it examines the UserAgent I am a seasoned asp.net web developer C# so go easy if you start talking about native to Windows Forms / WPF I can't seem to set the UserAgent setting in .net 4.0 - doesn't seem to be a property off the HttpWebRequest object for some reason - i think it used to be available. Silverlight 4.0 (created as 3.0 originally before I updated my installation of Silverlight to 4.0) Created using C# 4.0 Please explain as if you talking to a web developer and not a proper programming lol! Below is the code - it should return the XML from the wow armoury. private void button7_Click(object sender, RoutedEventArgs e) { // URL for armoury lookup string url = @"http://eu.wowarmory.com/guild-info.xml?r=Eonar&n=Gifted and Talented"; // Create the web request HttpWebRequest httpWebRequest = (HttpWebRequest)WebRequest.Create(url); // Set the user agent so we are returned XML and not HTML //httpWebRequest.Headers["User-Agent"] = "Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 6.0)"; // Not sure about this dispatcher thing - it's late so i have started to guess. Dispatcher.BeginInvoke(delegate() { // Call asyncronously IAsyncResult asyncResult = httpWebRequest.BeginGetResponse(ReqCallback, httpWebRequest); // End the response and use the result using (HttpWebResponse httpWebResponse = (HttpWebResponse)httpWebRequest.EndGetResponse(asyncResult)) { // Load an XML document from a stream XDocument x = XDocument.Load(httpWebResponse.GetResponseStream()); // Basic function that will use LINQ to XML to get the list of characters. ShowGuildies(x); } }); } private void ReqCallback(IAsyncResult asynchronousResult) { // Not sure what to do here - maybe update the interface? } Really hope someone out there can help me! Thanks mucho! Dan. PS Yes, I have noticed the irony in the name of the guild :)

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