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• I need to speed up a function. Should I use cython, ctypes, or something else?

  - by Peter Stewart

  I'm having a lot of fun learning Python by writing a genetic programming type of application. I've had some great advice from Torsten Marek, Paul Hankin and Alex Martelli on this site. The program has 4 main functions: generate (randomly) an expression tree. evaluate the fitness of the tree crossbreed mutate As all of generate, crossbreed and mutate call 'evaluate the fitness'. it is the busiest function and is the primary bottleneck speedwise. As is the nature of genetic algorithms, it has to search an immense solution space so the faster the better. I want to speed up each of these functions. I'll start with the fitness evaluator. My question is what is the best way to do this. I've been looking into cython, ctypes and 'linking and embedding'. They are all new to me and quite beyond me at the moment but I look forward to learning one and eventually all of them. The 'fitness function' needs to compare the value of the expression tree to the value of the target expression. So it will consist of a postfix evaluator which will read the tree in a postfix order. I have all the code in python. I need advice on which I should learn and use now: cython, ctypes or linking and embedding. Thank you.

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• How do I tell nant to only call csc when there are cs files in to compile?

  - by rob_g

  In my NAnt script I have a compile target that calls csc. Currently it fails because no inputs are specified: <target name="compile"> <csc target="library" output="${umbraco.bin.dir}\Mammoth.${project::get-name()}.dll"> <sources> <include name="project/*.cs" /> </sources> <references> </references> </csc> </target> How do I tell NAnt to not execute the csc task if there are no CS files? I read about the 'if' attribute but am unsure what expression to use with it, as ${file::exists('*.cs')} does not work. The build script is a template for Umbraco (a CMS) projects and may or may not ever have .cs source files in the project. Ideally I would like to not have developers need to remember to modify the NAnt script to include the compile task when .cs files are added to the project (or exclude it when all .cs files are removed).

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• C++: is it safe to work with std::vectors as if they were arrays?

  - by peoro

  I need to have a fixed-size array of elements and to call on them functions that require to know about how they're placed in memory, in particular: functions like glVertexPointer, that needs to know where the vertices are, how distant they are one from the other and so on. In my case vertices would be members of the elements to store. to get the index of an element within this array, I'd prefer to avoid having an index field within my elements, but would rather play with pointers arithmetic (ie: index of Element *x will be x - & array[0]) -- btw, this sounds dirty to me: is it good practice or should I do something else? Is it safe to use std::vector for this? Something makes me think that an std::array would be more appropriate but: Constructor and destructor for my structure will be rarely called: I don't mind about such overhead. I'm going to set the std::vector capacity to size I need (the size that would use for an std::array, thus won't take any overhead due to sporadic reallocation. I don't mind a little space overhead for std::vector's internal structure. I could use the ability to resize the vector (or better: to have a size chosen during setup), and I think there's no way to do this with std::array, since its size is a template parameter (that's too bad: I could do that even with an old C-like array, just dynamically allocating it on the heap). If std::vector is fine for my purpose I'd like to know into details if it will have some runtime overhead with respect to std::array (or to a plain C array): I know that it'll call the default constructor for any element once I increase its size (but I guess this won't cost anything if my data has got an empty default constructor?), same for destructor. Anything else?

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• A good solution for displaying galleries with lytebox and php

  - by Johann

  Hello I have thought for a while over an issue with the loading of images on a website-solution that I have programmed (For fun and the experience) The programming language used is PHP with MYSQL as the database language It also uses javascript, but not extensively I have recently realized that the engine I programmed, while it has it's smart solutions also carry a lot of flaws and redundant code. I have therefore decided to make a new one, now incorporating what I know, but didn't when I started the previous project. For the new system, there will be an option to add galleries to a site, and upload images to it. I have used the javascript image viewer Lytebox before. The screen goes dark and an image appears with a "Previous" and "next" button to view the other images. The problem is that I used groups with lytebox and the images themselves, resized as thumbs. This causes lytebox to work only when all the images have loaded. If you click a link before that, the image is shown as if you right click and choose "Show image" Information about these images is parsed from a database using a while statement with a counter that goes from 0 to sizeof() I'm thinking it probably isn't a good idea to have the images as the thumbs, even if you restrict the upload size. Likewise, adding thumbs at upload also seems like a hassle. It would be practical if the thumbs didn't show up before they were fully loaded. Has anyone got any good tips. Any help would be appreciated. Johann

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• Change Powerpoint chart data with .NET

  - by mc6688

  I have a Powerpoint template that contains 1 slide and on that slide is a chart. I'd like to be able to manipulate that charts data using .NET. So far I have code that... unzips the Powerpoint file. unzips the embedded excel file (ppt\embeddings\Microsoft_Office_Excel_Worksheet1.xlsx) It successfully manipulates the data in the excel sheet and zips it back up. Opens and manipulates ppt\charts\chart1.xml Powerpoint is then zipped up and delivered to the user The result of this is a Powerpoint file that shows a blank chart. But when I click on the chart and go to edit data it updates the data and shows the correct chart. I believe my problem is with the chart1.xml that I am generating. I have compared my generated version with a version created by Powerpoint and they are almost identical. The only differences are in the values for <c:crossAx> and <c:axId>. There are also some rounding difference in the data. But I do not feel like that would result in an blank chart. Is there another file that I need to edit? Does anyone have any ideas as to what else I should try to get this working?

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• How to make placeholder varablies in jquery validate 1.7?

  - by chobo2

  Hi I am using jquery 1.4.2 and jquery validate 1.7(http://bassistance.de/jquery-plugins/jquery-plugin-validation/) Say I have this example that I just grabbed off some random site(http://www.webreference.com/programming/javascript/jquery/form_validation/) 8 <script type="text/javascript"> 9 $(document).ready(function() { 10 $("#form1").validate({ 11 rules: { 12 name: "required",// simple rule, converted to {required:true} 13 email: {// compound rule 14 required: true, 15 email: true 16 }, 17 url: { 18 url: true 19 }, 20 comment: { 21 required: true 22 } 23 }, 24 messages: { 25 comment: "Please enter a comment." 26 } 27 }); 28 }); 29 </script> now is it possible to do something like this 10 $("#form1").validate({ var NameHolder = "name" 11 rules: { 12 NameHolder: "required",// simple rule, converted to {required:true} 13 email: {// compound rule 14 required: true, 15 email: true So basically I want to make sort of a global variable to hold theses rule names( what correspond to the names on that html control). My concern is the names of html controls can change and it kinda sucks that I will have to go around and change it in many places of my code to make it work again. So basically I am wondering is there away to make a global variable to store this name. So if I need to change the name I only have to change it in one spot in my javascript file sort of the way stopping magic numbers ?

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• UTF-8 HTML and CSS files with BOM (and how to remove the BOM with Python)

  - by Cameron

  First, some background: I'm developing a web application using Python. All of my (text) files are currently stored in UTF-8 with the BOM. This includes all my HTML templates and CSS files. These resources are stored as binary data (BOM and all) in my DB. When I retrieve the templates from the DB, I decode them using template.decode('utf-8'). When the HTML arrives in the browser, the BOM is present at the beginning of the HTTP response body. This generates a very interesting error in Chrome: Extra <html> encountered. Migrating attributes back to the original <html> element and ignoring the tag. Chrome seems to generate an <html> tag automatically when it sees the BOM and mistakes it for content, making the real <html> tag an error. So, using Python, what is the best way to remove the BOM from my UTF-8 encoded templates (if it exists -- I can't guarantee this in the future)? For other text-based files like CSS, will major browsers correctly interpret (or ignore) the BOM? They are being sent as plain binary data without .decode('utf-8'). Note: I am using Python 2.5. Thanks!

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• MS Word opens documents hosted on WebDav share read-only on Windows Vista and 7 but only if no other

  - by rjmunro

  We have a WebDav server with some Word documents on it. (We are using PHP's HTTP_WebDAV_Server but get the same issue on tests with Apache mod_dav - both use digest authentication, basic auth doesn't work on Vista or later) We have a web page that opens the word documents using javascript like: Doc = new ActiveXObject("Sharepoint.OpenDocuments.3"); Doc.EditDocument(url, 'Word.Document'); which causes word to connect to the webdav server and open the document, bypassing IE and most of windows built in WebDav client. On Windows XP, this works perfectly, and (after prompting you to log in) allows you to edit the word document and save it back to the server. On Windows 7 and Windows Vista, this usually opens the document read only, but not in all cases. After quite a bit of trial and error, we found that it worked (i.e. opened read/write) if Explorer happened to be already connected to a WebDav server. Note that this works with any Webdav server, not neccesarily the one with the document that you are trying to edit. So other than telling our users to change settings on their machine, is there anything we can do in the javascript sharepoint call, or on the WebDav server that will fix this issue. Ps. We have the same problem when launching Word from an HTA file version of our system, with javascript like: wordApp = new ActiveXObject("Word.application"); wordApp = new ActiveXObject("Word.application"); wordApp.Visible = true; doc = wordApp.Documents.Open(url); Pps. Sorry if you think this question should be on Serverfault (or even SuperUser). I couldn't decide, but because we are programming the WebDav server ourself (in PHP) and I have more rep on this site than the others, I decided to post it here :-)

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• Boost binding a function taking a reference

  - by Jamie Cook

  Hi all, I am having problems compiling the following snippet int temp; vector<int> origins; vector<string> originTokens = OTUtils::tokenize(buffer, ","); // buffer is a char[] array // original loop BOOST_FOREACH(string s, originTokens) { from_string(temp, s); origins.push_back(temp); } // I'd like to use this to replace the above loop std::transform(originTokens.begin(), originTokens.end(), origins.begin(), boost::bind<int>(&FromString<int>, boost::ref(temp), _1)); where the function in question is // the third parameter should be one of std::hex, std::dec or std::oct template <class T> bool FromString(T& t, const std::string& s, std::ios_base& (*f)(std::ios_base&) = std::dec) { std::istringstream iss(s); return !(iss >> f >> t).fail(); } the error I get is 1>Compiling with Intel(R) C++ 11.0.074 [IA-32]... (Intel C++ Environment) 1>C:\projects\svn\bdk\Source\deps\boost_1_42_0\boost/bind/bind.hpp(303): internal error: assertion failed: copy_default_arg_expr: rout NULL, no error (shared/edgcpfe/il.c, line 13919) 1> 1> return unwrapper<F>::unwrap(f, 0)(a[base_type::a1_], a[base_type::a2_]); 1> ^ 1> 1>icl: error #10298: problem during post processing of parallel object compilation Google is being unusually unhelpful so I hope that some one here can provide some insights.

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• Creating a simple command line interface (CLI) using a python server (TCP sock) and few scripts

  - by VN44CA

  I have a Linux box and I want to be able to telnet into it (port 77557) and run few required commands without having to access to the whole Linux box. So, I have a server listening on that port, and echos the entered command on the screen. (for now) Telnet 192.168.1.100 77557 Trying 192.168.1.100... Connected to 192.168.1.100. Escape character is '^]'. hello<br /> You typed: "hello"<br /> NOW: I want to create lot of commands that each take some args and have error codes. Anyone has done this before? It would be great if I can have the server upon initialization go through each directory and execute the init.py file and in turn, the init.py file of each command call into a main template lib API (e.g. RegisterMe()) and register themselves with the server as function call backs. At least this is how I would do it in C/C++. But I want the best Pythonic way of doing this. /cmd/ /cmd/myreboot/ /cmd/myreboot/ini.py (note underscore don't show for some reason) /cmd/mylist/ /cmd/mylist/init.py ... etc IN: /cmd/myreboot/_ini_.py: from myMainCommand import RegisterMe RegisterMe(name="reboot",args=Arglist, usage="Use this to reboot the box", desc="blabla") So, repeating this creates a list of commands and when you enter the command in the telnet session, then the server goes through the list, matches the command and passed the args to that command and the command does the job and print the success or failure to stdout. Thx

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• Are function-local typedefs visible inside C++0x lambdas?

  - by GMan - Save the Unicorns

  I've run into a strange problem. The following simplified code reproduces the problem in MSVC 2010 Beta 2: template <typename T> struct dummy { static T foo(void) { return T(); } }; int main(void) { typedef dummy<bool> dummy_type; auto x = [](void){ bool b = dummy_type::foo(); }; // auto x = [](void){ bool b = dummy<bool>::foo(); }; // works } The typedef I created locally in the function doesn't seem to be visible in the lambda. If I replace the typedef with the actual type, it works as expected. Here are some other test cases: // crashes the compiler, credit to Tarydon int main(void) { struct dummy {}; auto x = [](void){ dummy d; }; } // works as expected int main(void) { typedef int integer; auto x = [](void){ integer i = 0; }; } I don't have g++ 4.5 available to test it, right now. Is this some strange rule in C++0x, or just a bug in the compiler? From the results above, I'm leaning towards bug. Though the crash is definitely a bug. For now, I have filed two bug reports. All code snippets above should compile. The error has to do with using the scope resolution on locally defined scopes. (Spotted by dvide.) And the crash bug has to do with... who knows. :) Update According to the bug reports, they have both been fixed for the next release of Visual Studio 2010.

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• Uploading a file fails under WordPress

  - by Ash

  I'm using WordPress and I'm following W3's guide for uploading a file: HTML code: <html> <body> <form action="upload_file.php" method="post" enctype="multipart/form-data"> <label for="file">Filename:</label> <input type="file" name="file" id="file" /> <br /> <input type="submit" name="submit" value="Submit" /> </form> </body> </html> PHP code (upload_file.php): <?php if ($_FILES["file"]["error"] > 0) { echo "Error: " . $_FILES["file"]["error"] . "<br />"; } else { echo "Upload: " . $_FILES["file"]["name"] . "<br />"; echo "Type: " . $_FILES["file"]["type"] . "<br />"; echo "Size: " . ($_FILES["file"]["size"] / 1024) . " Kb<br />"; echo "Stored in: " . $_FILES["file"]["tmp_name"]; } ?> The HTML code is pasted in a PHP page template and the PHP file under the WP installation directory under www. The problem is when I submit the file I get Error: 1. If I remark the "if" part of the PHP code and leave the "else" part I get: Upload: IMG_4258.JPG Type: Size: 0 Kb Stored in: So at least I know the PHP code is running. But what's causing it to fail? Is there a problem with the code or is WordPress meddling with the process?

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• PHP Socket Server vs node.js: Web Chat

  - by Eliasdx

  I want to program a HTTP WebChat using long-held HTTP requests (Comet), ajax and websockets (depending on the browser used). Userdatabase is in mysql. Chat is written in PHP except maybe the chat stream itself which could also be written in javascript (node.js): I don't want to start a php process per user as there is no good way to send the chat messages between these php childs. So I thought about writing an own socket server in either PHP or node.js which should be able to handle more then 1000 connections (chat users). As a purely web developer (php) I'm not much familiar with sockets as I usually let web server care about connections. The chat messages won't be saved on disk nor in mysql but in RAM as an array or object for best speed. As far as I know there is no way to handle multiple connections at the same time in a single php process (socket server), however you can accept a great amount of socket connections and process them successive in a loop (read and write; incoming message - write to all socket connections). The problem is that there will most-likely be a lag with ~1000 users and mysql operations could slow the whole thing down which will then affect all users. My question is: Can node.js handle a socket server with better performance? Node.js is event-based but I'm not sure if it can process multiple events at the same time (wouldn't that need multi-threading?) or if there is just an event queue. With an event queue it would be just like php: process user after user. I could also spawn a php process per chat room (much less users) but afaik there are singlethreaded IRC servers which are also capable to handle thousands of users. (written in c++ or whatever) so maybe it's also possible in php. I would prefer PHP over Node.js because then the project would be php-only and not a mixture of programming languages. However if Node can process connections simultaneously I'd probably choose it.

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• Python, Ruby, and C#: Use cases?

  - by thaorius

  Hi everyone. For as long as I can remember, I've always had a "favorite" language, which I use for most projects, until, for some particular reason, there is no way/point on using it for project XYZ. At that point, I find myself rusty (and sometimes outdated) on other languages+libraries+toolchains. So I decided, I would just use some languages/libs/tools for some things, and some for other, effectively keeping them fresh (there would obviously be exceptions, I'm not looking for an arbitrary rule set, but some guidelines). I wanted an opinion on what would be your standard use cases (new projects) for Python, Ruby, and C# (Mono). At the moment, I have time like this:Languages: C#: Mid-Large Sized Projects (mainly server-side daemons) High Performance (I hardly ever need C's performance, but Python just doesn't cut it) Relatively Low Footprint (vs the JVM, for example) Ruby: Web Applications Python: General Use Scripts (automation, system config, etc) Small-Mid Sized Projects Prototyping Web Applications About Ruby, I have no idea what to use it for that I can't use Python for (specially considering Python is more easily found installed by default). And I like both languages (though I'm really new to Ruby), which makes things even worse. As for C#, I have not used a Windows powered computer in a few years, I don't make things for Windows computers, and I don't mind waiting for Mono to implement some new features. That being said, I haven't found many people on the internet using it for server-sided *nix programming (not web related). I would appreciate some insight on this too. Thanks for your time.

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• Python: Access dictionary value inside of tuple and sort quickly by dict value

  - by Aquat33nfan

  I know that wasn't clear. Here's what I'm doing specifically. I have my list of dictionaries here: dict = [{int=0, value=A}, {int=1, value=B}, ... n] and I want to take them in combinations, so I used itertools and it gave me a tuple (Well, okay it gave me a memory object that I then used enumerate on so I could loop over it and enumerate gave ma tuple): for (index, tuple) in enumerate(combinations(dict, 2)): and this is where I have my problem. I want to identify which of the two items in the combination has the bigger 'int' value and which has the smaller value and assign them to variables (I'm actually using more than 2 in the combination so I can't just say if tuple[0]['int'] tuple[1]['int'] and do the assignment because I'd have to list this out a bunch of times and that's hard to manage). I was going to assign each 'int' value to a variable, sort it in a list, index the 'int' value in the list by 1, 2, 3, 4, 5 ... etc., then go back and access the dictionary I wanted by the int value and then assign the dictionary to a variable so I knew which was bigger. But I have a big list and lists and variable assignments are resource intensive and this is taking a long time (I had only a little bit of that written and it was taking forever to run). So I was hoping someone knew a fast way to do this. I actually could list out every possible combination of assignmnets using the if/thens but it's just like 5 pages of if/thens and assignments and is hard to read and manage when I want to change it. You've probably gathered this, but I"m new at programming. thx

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• .NET: Control Invoke() in Reflector

  - by sheepsimulator

  So, I was getting back into some .NET programming, and through a new feature in VS.NET 2010, it detected a case where I was trying to modify a control from a thread that didn't create that control, and pointed me to an article on MSDN about how you do this correctly... ' HOW TO WRITE TO A FORM CONTROL FROM A THREAD THAT DIDN'T CREATE THE CONTROL ' =========================================================================== ' Say you need to write to a UI text box that logs stuff... Delegate Sub WriteLogDelegate(ByVal [text] As String) Private Sub WriteLog(ByVal [text] As String) If Me.rtfLog.InvokeRequired Then ' We are not in the same thread! ' Create new WriteLogDelegate and invoke it on the same thread Dim d As New WriteLogDelegate(AddressOf WriteLog) Me.rtfLog.Invoke(d, New Object() {[text]}) Else ' We are totally in the same thread... ' Call AppendText like normal! Me.rtfLog.AppendText([text]) End If End Sub AND I WAS SO EXCITED BECAUSE I HAVE BEEN PUZZLED BY HOW TO DO THIS FOR LIKE 5 YEARS BECAUSE PREVIOUS VERSIONS OF VS.NET DIDN'T FLAG THIS SINCE I WAS AN UNDERGRAD ON A PROJECT AND... Umm... Sorry bout that. Composure regained. Anyway, now that I know this bit of .NET-fu, I'd like to learn more about what's going on and how it works. Where can I find the code for Invoke() in .NET Reflector?

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• Using boost asio for pub/sub style tcp in a game loop

  - by unohoo

  I have been reading through the boost asio documentation for a couple of hours now, and while I think the documentation is really great, I am still left a bit confused on how to implement the system that I need. I have to stream info, from a game engine, to a list of computers over tcp. One snag is that, unlike traditional pub/sub, the computer that does the distribution of info is actually the computer that has to connect to the subscribers as well (instead of the subscribers registering with the publisher). This is done via a config file - a list of ip's/ports along with the data that they each require. The subscribers listen, but do not know the ip of the publisher. (As a side note, I'm quite new to network programming, so maybe I'm missing something .. but it's strange that I do not find much information regarding this style of "inverted" client-server model..) I am looking for suggestions for the implementation of such a system using boost asio. Of course I have to integrate the networking into an already existing engine, so with regards to that: What would be a good way to handle messages being sent to multiple computers every frame? Use async_write, call io_service.run and then reset every frame? Would having io_service.run have its own thread be better? Or should I just use threads and use blocking writes?

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• Looking for a very simple file-based CMS

  - by nfm

  I'm building a site for a friend for free, and am trying to work out a good way for her to be able to easily make updates. I haven't used any CMSs before. I was browsing the web today looking at some, and they all seem way too complicated for what I'm after. Basically, all I want is a really simple CMS that pulls together HTML snippets in particular subdirectories, and wraps them in header/footer HTML and inserts them into a template page in the appropriate section. I'm imagining a site layout something like this: / /index.php /blog_template.php /news_template.php /blog/ /blog/header.php /blog/footer.php /blog/my-first-blog.html /blog/blogs-rule.html /blog/... Say index.php contains div#blog. PHP would wrap each /blog/*.html file in /blog/header.php and blog/footer.php, and insert them into the div#blog as div#blog([0-9]*). I haven't been able to find anything this basic, and am one step away from throwing something together myself, but I'm a bit short on time at the moment and figured I'd post here first. Has anyone come across something like this? I don't want any DB, extensions, user accounts, installation, config, updates... just a simple file based solution. Thanks :) Forgot to mention - needs to be FOSS and run on Linux!

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• Difference in BackgroundWorker thread access in VS2010 / .NET 4.0?

  - by Jonners

  Here's an interesting one - in VS2005 / VS2008 running against .NET 2.0 / .NET 3.0 / .NET 3.5, a BackgroundWorker thread may not directly update controls on a WinForms form that initiated that thread - you'll get a System.InvalidOperationException out of the BackgroundWorker stating "Cross-thread operation not valid: Control 'thecontrol' accessed from a thread other than the thread it was created on". I remember hitting this back in 2004 or so when I first started writing .NET WinForms apps with background threads. There are several ways around the problem - this is not a question asking for that answer. I've been told recently that this kind of operation is now allowed when written in VS2010 / .NET 4.0. This seems unlikely to me, since this kind of object access restriction has always been a fairly fundamental part of thread-safe programming. Allowing a BackgroundWorker thread direct access to objects owned not by itself but by its parent UI form seems contrary to that principle. A trawl through the .NET 4.0 docs hasn't revealed any obvious changes that could account for this behaviour. I don't have VS2010 / .NET 4.0 to test this out - does anyone who has access to that toolset know for sure whether the model has changed to allow that kind of thread interaction? I'd like to either take advantage of it in future, or deploy the cluestick. ;)

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• How to generate lots of redundant ajax elements like checkboxes and pulldowns in Django?

  - by iJames

  Hello folks. I've been getting lots of answers from stackoverflow now that I'm in Django just be searching. Now I hope my question will also create some value for everybody. In choosing Django, I was hoping there was some similar mechanism to the way you can do partials in ROR. This was going to help me in two ways. One was in generating repeating indexed forms or form elements, and also in rendering only a piece of the page on the round trip. I've done a little bit of that by using taconite with a simple URL click but now I'm trying to get more advanced. This will focus on the form issue which boils down to how to iterate over a secondary object. If I have a list of photo instances, each of which has a couple of parameters, let's say a size and a quantity. I want to generate form elements for each photo instance separately. But then I have two lists I want to iterate on at the same time. Context: photos : Photo.objects.all() and forms = {} for photo in photos: forms[photo.id] = PhotoForm() In other words we've got a list of photo objects and a dict of forms based on the photo.id. Here's an abstraction of the template: {% for photo in photos %} {% include "photoview.html" %} {% comment %} So here I want to use the photo.id as an index to get the correct form. So that each photo has its own form. I would want to have a different action and each form field would be unique. Is that possible? How can I iterate on that? Thanks! {% endcomment %} Quantity: {{ oi.quantity }} {{ form.quantity }} Dimensions: {{ oi.size }} {{ form.size }} {% endfor %} What can I do about this simple case. And how can I make it where every control is automatically updating the server instead of using a form at all? Thanks! James

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• Fastest inline-assembly spinlock

  - by sigvardsen

  I'm writing a multithreaded application in c++, where performance is critical. I need to use a lot of locking while copying small structures between threads, for this I have chosen to use spinlocks. I have done some research and speed testing on this and I found that most implementations are roughly equally fast: Microsofts CRITICAL_SECTION, with SpinCount set to 1000, scores about 140 time units Implementing this algorithm with Microsofts InterlockedCompareExchange scores about 95 time units Ive also tried to use some inline assembly with __asm {} using something like this code and it scores about 70 time units, but I am not sure that a proper memory barrier has been created. Edit: The times given here are the time it takes for 2 threads to lock and unlock the spinlock 1,000,000 times. I know this isn't a lot of difference but as a spinlock is a heavily used object, one would think that programmers would have agreed on the fastest possible way to make a spinlock. Googling it leads to many different approaches however. I would think this aforementioned method would be the fastest if implemented using inline assembly and using the instruction CMPXCHG8B instead of comparing 32bit registers. Furthermore memory barriers must be taken into account, this could be done by LOCK CMPXHG8B (I think?), which guarantees "exclusive rights" to the shared memory between cores. At last [some suggests] that for busy waits should be accompanied by NOP:REP that would enable Hyper-threading processors to switch to another thread, but I am not sure whether this is true or not? From my performance-test of different spinlocks, it is seen that there is not much difference, but for purely academic purpose I would like to know which one is fastest. However as I have extremely limited experience in the assembly-language and with memory barriers, I would be happy if someone could write the assembly code for the last example I provided with LOCK CMPXCHG8B and proper memory barriers in the following template: __asm { spin_lock: ;locking code. spin_unlock: ;unlocking code. }

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• C++ iterators, default initialization and what to use as an uninitialized sentinel.

  - by Hassan Syed

  The Context I have a custom template container class put together from a map and vector. The map resolves a string to an ordinal, and the vector resolves an ordinal (only an initial string to ordinal lookup is done, future references are to the vector) to the entry. The entries are modified intrusively to contain a a bool "assigned" and an iterator_type which is a const_iterator to the container class's map. My container class will use RCF's serialization code (which models boost::serialization) to serialize my container classes to nodes in a network. Serializing iterator's is not possible, or a can of worms, and I can easily regenerate them onces the vectors and maps are serialized on the remote site. The Question I need to default initialize, and be able to test that the iterator has not been assigned to (if it is assigned it is valid, if not it is invalid). Since map iterators are not invalidated upon operations performed on it (unless of course items are removed :D) am I to assume that map<x,y>::end() is a valid sentinel (regardless of the state of the map -- i.e., it could be empty) to initialize to ? I will always have access to the parent map, I'm just unsure wheather end() is the same as the map contents change. I don't want to use another level of indirection (--i.e., boost::optional) to achieve my goal, I'd rather forego compiler checks to correct logic, but it would be nice if I didn't need to. Misc This question exists, but most of its content seems non-sense. Assigning a NULL to an iterator is invalid according to g++ and clang++. This is another similar question, but it focuses on the common use-cases of iterators, which generally tends to be using the iterator to iterate, ofcourse in this use-case the state of the container isn't meant to change whilst iteration is going on.

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• How to define a default tooltip style for all Controls

  - by skjagini

  I would like to define a style with a template when there are validation errors and would display the first error message as a tooltip. It works fine when targeting specific control like DatePicker in the following xaml. <Style TargetType="{x:Type ToolKit:DatePicker}"> <Style.Triggers> <Trigger Property="Validation.HasError" Value="true"> <Setter Property="ToolTip" Value="{Binding RelativeSource={RelativeSource Self}, Path=(Validation.Errors)[0].ErrorContent}"/> </Trigger> </Style.Triggers> </Style> I cannot get it to work for Control though, i.e. the following doesn't give any tooltip <Style TargetType="{x:Type ToolKit:Control}"> <Style.Triggers> <Trigger Property="Validation.HasError" Value="true"> <Setter Property="ToolTip" Value="{Binding RelativeSource={RelativeSource Self}, Path=(Validation.Errors)[0].ErrorContent}"/> </Trigger> </Style.Triggers> </Style> Any idea?

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• Alignment in assembly

  - by jena

  Hi, I'm spending some time on assembly programming (Gas, in particular) and recently I learned about the align directive. I think I've understood the very basics, but I would like to gain a deeper understanding of its nature and when to use alignment. For instance, I wondered about the assembly code of a simple C++ switch statement. I know that under certain circumstances switch statements are based on jump tables, as in the following few lines of code: .section .rodata .align 4 .align 4 .L8: .long .L2 .long .L3 .long .L4 .long .L5 ... .align 4 aligns the following data on the next 4-byte boundary which ensures that fetching these memory locations is efficient, right? I think this is done because there might be things happening before the switch statement which caused misalignment. But why are there actually two calls to .align? Are there any rules of thumb when to call .align or should it simply be done whenever a new block of data is stored in memory and something prior to this could have caused misalignment? In case of arrays, it seems that alignment is done on 32-byte boundaries as soon as the array occupies at least 32 byte. Is it more efficient to do it this way or is there another reason for the 32-byte boundary? I'd appreciate any explanation or hint on literature.

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• C++ cin whitespace question

  - by buddyfox

  Programming novice here. I'm trying to allow a user to enter their name, firstName middleName lastName on one line in the console (ex. "John Jane Doe"). I want to make the middleName optional. So if the user enters "John Doe" it only saves the first and last name strings. If the user enters "John Jane Doe" it will save all three. I was going to use this: cin >> firstName >> middleName >> lastName; then I realized that if the user chooses to omit their middle name and enters "John Doe" the console will just wait for the user to enter a third string... I know I could accomplish this with one large string and breaking it up into two or three, but isn't there a simpler way to do it with three strings like above? I feel like I'm missing something simple here... Thanks in advance.

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