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• [iPhone] UIScrollView notifications

  - by ryyst

  Hi, I'm coding an app that works much like Apple's Weather.app: There's a UIPageControl at the bottom and a UIScrollView in the middle of the screen. In my code, I implemented the - (void)scrollViewDidEndDecelerating:(UIScrollView *)scrollView method to figure out when the user did move to a new page. If they move to a new page, I load the adjacent pages' data, as to make further page-switching faster. (In one of Apple's examples, the - (void)scrollViewDidScroll:(UIScrollView *)sender is used, but that causes my app to shortly hang when loading a new page, so it's not suitable.) That code works very well. I'm using scrollRectToVisible:: to programmatically scroll inside the scrollview when the user clicks the UIPageControl. The problem is that the scrollRectToVisible: doesn't post a notification to the UIScrollViewDelegate when it's done scrolling - so the code responsible for loading adjacent pages never get's called when using the UIPageControl. Is there any way to make the UIScrollView notify its delegate when it gets called by the scrollRectToVisible: method? Or will I have to use threads in order to prevent my app from freezing? Thanks! -- Ry

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• How do I make software that preserves database integrity and correctness?

  - by user287745

  I have made an application project in Visual Studio 2008 C#, SQL Server from Visual Studio 2008. The database has like 20 tables and many fields in each. I have made an interface for adding deleting editing and retrieving data according to predefined needs of the users. Now I have to Make to project into software which I can deliver to my professor. That is, he can just double click the icon and the software simply starts. No Visual Studio 2008 needed to start the debugging. The database will be on one powerful computer (dual core latest everything Windows XP) and the user will access it from another computer connected using LAN. I am able to change the connection string to the shared database using Visual Studio 2008/ debugger whenever the server changes but how am I supposed to do that when it's software? There will by many clients. Am I supposed to give the same software to every one, so they all can connect to the database? How will the integrity and correctness of the database be maintained? I mean the db.mdf file will be in a folder which will be shared with read and write access. So it's not necessary that only one user will write at a time. So is there any coding for this or?

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• Fast Lightweight Image Comparisson Metric Algorithm

  - by gav

  Hi All, I am developing an application for the Android platform which contains 1000+ image filters that have been 'evolved'. When a user selects a photo I want to present the most relevant filters first. This 'relevance' should be dependent on previous use cases. I have already developed tools that register when a filtered image is saved; this combination of filter and image can be seen as the training data for my system. The issue is that the comparison must occur between selecting an image and the next screen coming up. From a UI point of view I need the whole process to take less that 4 seconds; select an image- obtain a metric to use for similarity - check against use cases - return 6 closest matches. I figure with 4 seconds I can use animations and progress dialogs to keep the user happy. Due to platform contraints I am fairly limited in the computational expense of the algorithm. I have implemented a technique adapted from various online tutorials for running C code on the G1 and hence this language is available Specific Constraints; Qualcomm® MSM7201A™, 528 MHz Processor 320 x 480 Pixel bitmap in 32 bit ARGB ~ 2 seconds computational time for the native method to get the metric ~ 2 seconds to compare the metric of the current image with training data This is an academic project so all ideas are welcome, anything you can think of or have heard about would be of interest to me. My ideas; I want to keep the complexity down (O(n*m)?) by using pixel data only rather than a neighbourhood function I was looking at using the Colour historgram/Greyscale histogram/Texture/Entropy of the image, combining them to make the measure. There will be an obvious loss of information but I need the resultant metric to be substantially smaller than the memory footprint of the image (~0.512 MB) As I said, any ideas to direct my research would be fantastic. Kind regards, Gavin

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• Why does the Java Collections Framework offer two different ways to sort?

  - by dvanaria

  If I have a list of elements I would like to sort, Java offers two ways to go about this. For example, lets say I have a list of Movie objects and I’d like to sort them by title. One way I could do this is by calling the one-argument version of the static java.util.Collections.sort( ) method with my movie list as the single argument. So I would call Collections.sort(myMovieList). In order for this to work, the Movie class would have to be declared to implement the java.lang.Comparable interface, and the required method compareTo( ) would have to be implemented inside this class. Another way to sort is by calling the two-argument version of the static java.util.Collections.sort( ) method with the movie list and a java.util.Comparator object as it’s arguments. I would call Collections.sort(myMovieList, titleComparator). In this case, the Movie class wouldn’t implement the Comparable interface. Instead, inside the main class that builds and maintains the movie list itself, I would create an inner class that implements the java.util.Comparator interface, and implement the one required method compare( ). Then I'd create an instance of this class and call the two-argument version of sort( ). The benefit of this second method is you can create an unlimited number of these inner class Comparators, so you can sort a list of objects in different ways. In the example above, you could have another Comparator to sort by the year a movie was made, for example. My question is, why bother to learn both ways to sort in Java, when the two-argument version of Collections.sort( ) does everything the first one-argument version does, but with the added benefit of being able to sort the list’s elements based on several different criteria? It would be one less thing to have to keep in your mind while coding. You’d have one basic mechanism of sorting lists in Java to know.

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• Matlab Simulation: Point (symbol) Moving from start point to end point and back

  - by niko

  Hi, I would like to create an animation to demonstrate LDPC coding which is based on Sum-Product Algorithm So far I have created a graph which shows the connections between symbol nodes (left) and parity nodes (right) and would like to animate points travelling from symbol to parity nodes and back. The figure is drawn by executing the following method: function drawVertices(H) hold on; nodesCount = size(H); parityNodesCount = nodesCount(1); symbolNodesCount = nodesCount(2); symbolPoints = zeros(symbolNodesCount, 2); symbolPoints(:, 1) = 0; for i = 0 : symbolNodesCount - 1 ji = symbolNodesCount - i; scatter(0, ji) symbolPoints(i + 1, 2) = ji; end; parityPoints = zeros(parityNodesCount, 2); parityPoints(:, 1) = 10; for i = 0 : parityNodesCount - 1 ji = parityNodesCount - i; y0 = symbolNodesCount/2 - parityNodesCount/2; scatter(10, y0 + ji) parityPoints(i + 1, 2) = y0 + ji; end; axis([-1 11 -1 symbolNodesCount + 2]); axis off %connect vertices d = size(H); for i = 1 : d(1) for j = 1 : d(2) if(H(i, j) == 1) plot([parityPoints(i, 1) symbolPoints(j, 1)], [parityPoints(i, 2) symbolPoints(j, 2)]); end; end; end; So what I would like to do here is to add another method which takes start point (x and y) and end point as arguments and animates a travelling circle (dot) from start to end and back along the displayed lines. I would appreciate if anyone of you could show the solution or suggest any useful tutorial about matlab simulations. Thank you!

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• Really simple JSON serialization in .NET

  - by Evgeny

  I have some simple .NET objects I'd like to serialize to JSON and back again. The set of objects to be serialized is quite small and I control the implementation, so I don't need a generic solution that will work for everything. Since my assembly will be distributed as a library I'd really like to avoid a dependency on some third-party DLL: I just want to give users one assembly that they can reference. I've read the other questions I could find on converting to and from JSON in .NET. The recommended solution of JSON.NET does work, of course, but it requires distributing an extra DLL. I don't need any of the fancy features of JSON.NET. I just need to handle a simple object (or even dictionary) that contains strings, integers, DateTimes and arrays of strings and bytes. On deserializing I'm happy to get back a dictionary - it doesn't need to create the object again. Is there some really simple code out there that I could compile into my assembly to do this simple job? I've also tried System.Web.Script.Serialization.JavaScriptSerializer, but where it falls down is the byte array: I want to base64-encode it and even registering a converter doesn't let me easily accomplish that due to the way that API works (it doesn't pass in the name of the field).

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• [EF 4 POCO] Problem with INSERT...

  - by Darmak

  Hi all, I'm so frustrated because of this problem, you have no idea... I have 2 classes: Post and Comment. I use EF 4 POCO support, I don't have foreign key columns in my .edmx model (Comment class doesn't have PostID property, but has Post property) class Comment { public Post post { get; set; } // ... } class Post { public virtual ICollection<Comment> Comments { get; set; } // ... } Can someone tell me why the code below doesn't work? I want to create a new comment for a post: Comment comm = context.CreateObject<Comment>(); Post post = context.Posts.Where(p => p.Slug == "something").SingleOrDefault(); // post != null, so don't worry, be happy // here I set all other comm properties and... comm.Post = post; context.AddObject("Comments", comm); // Exception here context.SaveChanges(); The Exception is: Cannot insert the value NULL into column 'PostID', table 'Blog.Comments'; column does not allow nulls. INSERT fails. ... this 'PostID' column is of course a foreign key to the Posts table. Any help will be appreciated!

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• N-son tabbed/JsScrollbar, trying to force gif play from click of link using jquery

  - by user314286

  Hello everyone, Let me start off by stating the obvious; I am new here. That said I hope I am not violating some standard I missed by posting this. xD For several days now I've been trying to update a rather old site of mine, to which I wont link to given that the update is so drastic that the current product on which I seek your help for doesn't resemble the old site in any other way then appearance. Anywho! I am using the tabbed div and JsScrollbar created by N-son (http://www.downloadjavascripts.com/list/javasitek60/Details.aspx) and so far have only used jquery to dynamically center content on the page. My problem however is this...I have a gif on the page that acts as a background (it's not tiled) and I'd like to be able to have it so that when you click on one of the links used in n-sons tabs (EX: news) it also causes the gif to load and play through itself once. So far all my attempts at accomplishing this myself have failed and break wither the scrollbar or prevent the content from switching when you click the tabs. (Except for one failed attempt where it all worked fine except the handle for the scrollbar would vanish upon switching tabs) I hope I've been clear in this and that someone is able to help. I know it may seem like a silly question but we're all new at some point. :P If need be I'll upload what coding I have but it is not pretty. Thank you in advance.

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• jquery ajax html response change 1.3.2 vs 1.4.2 (aka where is my script tag?)

  - by cmroanirgo

  I've been using jquery 1.3.2 to pull snippets of html (including script) from a server. A typical response might be: <div id="content"<div id="inner"... <script type=... alert("hello world");</script <pHello World</p </div</div I've been using the query .get function: $.get($(this).attr("href"), function(response) { $("#inner").replaceWith($("#inner", response)); }); And everything is fine and works as expected: the returned html snippets get loaded into the DOM and the scripts run. When I use 1.4.2 however, I notice that the script tags have been removed and no longer run. Stepping into the newer jquery codebase yields the lines of code (line 4498) : ret.splice.apply( ret, [i + 1, 0].concat(jQuery.makeArray(ret[i].getElementsByTagName("script"))) ); which seems to be the culprit 'removing' the script from its happy resting place as part of the selector process. But it doesn't help me in injecting exactly what i want into the DOM. Any idea why jquery is doing this? More importantly, how can I go about fixing this so that my scripts run?

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• How do I write a J2EE/EJB Singleton?

  - by Bears will eat you

  A day ago my application was one EAR, containing one WAR, one EJB JAR, and a couple of utility JAR files. I had a POJO singleton class in one of those utility files, it worked, and all was well with the world: EAR |--- WAR |--- EJB JAR |--- Util 1 JAR |--- Util 2 JAR |--- etc. Then I created a second WAR and found out (the hard way) that each WAR has its own ClassLoader, so each WAR sees a different singleton, and things break down from there. This is not so good. EAR |--- WAR 1 |--- WAR 2 |--- EJB JAR |--- Util 1 JAR |--- Util 2 JAR |--- etc. So, I'm looking for a way to create a Java singleton object that will work across WARs (across ClassLoaders?). The @Singleton EJB annotation seemed pretty promising until I found that JBoss 5.1 doesn't seem to support that annotation (which was added as part of EJB 3.1). Did I miss something - can I use @Singleton with JBoss 5.1? Upgrading to JBoss AS 6 is not an option right now. Alternately, I'd be just as happy to not have to use EJB to implement my singleton. What else can I do to solve this problem? Basically, I need a semi-application-wide* hook into a whole bunch of other objects, like various cached data, and app config info. As a last resort, I've already considered merging my two WARs into one, but that would be pretty hellish. *Meaning: available basically anywhere above a certain layer; for now, mostly in my WARs - the View and Controller (in a loose sense).

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• Benefits of migrating my work to a new web development framework?

  - by John

  When I first started programming with PHP, I was ignorant of other php frameworks (like code igniter, cake php, etc...). So I fell into the trap of re-inventing wheels, which had the benefit of being "fun" and "educational". Overtime, I discovered other open source products that I found useful, like smarty templating engine, jquery library, tcpdf library, fdf etc...so I started bundling these technologies along with things I've built over the years into a LAMP development framework to make life easier for myself. This pass year, I've been having fun developing on the code igniter framework. It does many of the things I do in my framework. Coding in CI feels natural because the MVC and ORM feels similar to the MVC and ORM of my framework. So now I'm contemplating migrating a lot of the plugins in my framework over to CI. The pros and cons I can think of for such a project are: Pros: benefit from the vast community of CI developers lots of other developers will be familiar with it better documentation Cons: I've built a lot of useful plugins against my own framework, and it will take a lot of time to move even just the essential ones at the moment, I still, work faster against my own framework than CI, just because I'm more familiar with it even if I did migrate to CI, there will always be newer and better frameworks in the near future, and i'll be contemplating this scenario again So my question is the following: perhaps I should leave my old framework as is, and for each new project I receive, I make a decision on whether the requirements are best served by developing with CI or my own framework. Is this the right approach?

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• Is a "factory" method the right pattern?

  - by jdt141

  Hey all - So I'm working to improve an existing implementation. I have a number of polymorphic classes that are all composed into a higher level container class. The problem I'm dealing with at the moment is that the higher level container class, well, sucks. It looks something like this, which I really don't have a problem with (as the polymorphic classes in the container should be public). My real issue is the constructor... /* * class1 and class 2 derive from the same superclass */ class Container { public: boost::shared_ptr<ComposedClass1> class1; boost::shared_ptr<ComposedClass2> class2; private: ... } /* * Constructor - builds the objects that we need in this container. */ Container::Container(some params) { class1.reset(new ComposedClass1(...)); class2.reset(new ComposedClass2(...)); } What I really need is to make this container class more re-usable. By hard-coding up the member objects and instantiating them, it basically isn't and can only be used once. A factory is one way to build what I need (potentially by supplying a list of objects and their specific types to be created?) Other ways to get around this problem? Seems like someone should have solved it before... Thanks!

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• What is a good programming language/environment for Linux database applications?

  - by Dkellygb

  I could use some advice on my move from the Windows world to Linux. For my business, I have used VB6 and Microsoft Access with both Access databases and SQL server in the past. The easy to use forms, report writers and programming language were perfect for CRUD apps and analysis for our small hotel/restaurant business. After using Linux at home for some time I would like to convert our small business. Our server is already a Linux box using Samba. I am happy with the OpenOffice.org applications instead of Microsoft Office. The only thing which is holding me back is a desktop database application where I can develop the forms and reports we require. Base does not seem to be up to the job yet from my experience. I would like something like VB.Net with visual studio (express) but I would like to avoid Mono – I just don’t see the point of it. (You can correct me if I’m wrong.) But a good collection of forms, controls and a good report writer would be ideal. I have looked at web based stuff like Ruby on Rails, but I think a webserver for our 5 pc network is overkill. I don’t mind running a proper database on our Ubuntu 9.10 server. I may have exposed a few prejudices above but my mind is open. Any thoughts?

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• Intercepting hyperlinks in an embedded Word document

  - by Ryan

  Hello, I'm working on an app which uses embedded Word documents. We have a feature which allows them to insert a small clickable image into the doc - when the user clicks on it, we want the app to open another window based on some data specified by the user when the image was added. What the application does now is: When the image is inserted, the app creates a hyperlink for it and the data is used as the link destination The user ctrl+clicks on the image and the Word document the WindowSelectionChange event The app handles the WindowSelectionChange event and goes to open the specified window This approach worked fine with previous versions, when we had the 11.0 / Word 2003 interop dll's. We upgraded to 12.0/Word 2007 for the upcoming release, and in many cases the event is not firing when I click on the image - sometimes it does, sometimes it doesn't, and I'm descending into the cargo-cult world trying to figure out why - sometimes saving and re-opening the document works, sometimes killing the Word process and starting a new one fixes (or breaks) the feature. My guess is there's something going wrong with the WinSelChg event, but I'm not sure what. The usual process we have for applying the event handler is: try //remove the old one if any { ((Document)myAXFramerControl.ActiveDocument).Application.WindowSelectionChange -= new ApplicationEvents4_WindowSelectionChangeEventHandler(WSC_eventhandlerfunction); } catch{} ((Document)myAXFramerControl.ActiveDocument).Application.WindowSelectionChange += new ApplicationEvents4_WindowSelectionChangeEventHandler(WSC_eventhandlerfunction); Sometimes one or both of these will throw exceptions - usually a NullReferenceException when removing the handler. Adding the handler sometimes throws the "com object that has been separated from its underlying rcw cannot be used" exception, which I don't understand at all - my impression was that this only occurs when you, say, store a reference to the Word application or document and try to use it later. As it stands the WSC event handler is frequently never run; while I'm happy to fiddle with the app until it works once I can't really expect the same of the users who have been happily using this feature for a while now. Any ideas?

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• Gracefully handling screen orientation change during activity start

  - by Steve H

  I'm trying to find a way to properly handle setting up an activity where its orientation is determined from data in the intent that launched it. This is for a game where the user can choose levels, some of which are int portrait orientation and some are landscape orientation. The problem I'm facing is that setRequestedOrientation(ActivityInfo.SCREEN_ORIENTATION_LANDSCAPE) doesn't take effect until the activity is fully loaded. This is a problem for me because I do some loading and image processing during startup, which I'd like to only have to do once. Currently, if the user chose a landscape level: the activity starts onCreate(), defaulting to portrait discovers from analysing its launching Intent that it should be in landscape orientation continues regardless all the way to onResume(), loading information and performing other setup tasks at this point setRequestedOrientation kicks in so the application runs through onPause() to onDestroy() it then again starts up from onCreate() and runs to onResume() repeating the setup from earlier Is there a way to avoid that and have it not perform the loading twice? For example, ideally, the activity would know before even onCreate was called whether it should be landscape or portrait depending on some property of the launching intent, but unless I've missed something that isn't possible. I've managed to hack together a way to avoid repeating the loading by checking a boolean before the time-consuming loading steps, but that doesn't seem like the right way of doing it. I imagine I could override onSaveInstanceState, but that would require a lot of additional coding. Is there a simple way to do this? Thanks!

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• C++ : Avoid lot of boolean variable for multiple verification conditions in trading app

  - by Naveen

  Hi i am a junior dev in trading app... we have a order refresh verification unit. It has to verify order confirmation from exchange. We send a bunch of different request in bulk ( NEW, MODIFY, CANCEL ) to exchange... Verification has to happen for max N times with each T intervals for all orders. if verification successful for all the order before N retry then fine.. otherwise we need to indicate as verification unsuccessfull. i hv done a basic coding done in very urgent like below for( N times ) { for_each ( sent_request_order ) // SENT { 1) get all the refreshed order from DB or shared mem i.e REFRESHED 2) find current sent order in REFRESHED if( not_found ) not refreshed from exchange, continue to next order if( found ) case NEW : //check for new status, mark verification done case MODIFY : //check for modified status.. //if not mark pending, go to next order, //revisit the same after T time case CANCEL : //check for cancelled status.. //if not mark pending, go to next order, //revisit the same after T time } if( all_verified ) exit from verification. wait ( T sec ) } order_verification_pending, order_verification_done, order_visited, order_not_visited, all_verified, all_not_verified ... lot of boolean flags used for indication.. is there any better approach for doing this.... splitting responsibilities across the classes......???? i know this is not a general question.... but still flags are making me tidious to handle...

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• How to prevent linq-to-sql designer undo my changing

  - by anonim.developer

  Dear All, Thanks for your attention in advance, I’ve met an issue with LINQ-2-SQL designer in VS 2008 SP1 which has made me CRAZY. I use Linq2sql as my DAL. It seems Linq2sql speeds up coding in the first step but lots of issues arise in feature specifically with table or object inheritance. In this case I have a class Entity that all other entity classes generated by Linq2sql designer inherit from. public abstract class Entity { public virtual Guid ID { get; protected set; } } public partial class User : monius.Data.Entity { } And the following generated by L2S designer (DataModel.designer.cs) [Column(Storage = "_ID", AutoSync = AutoSync.OnInsert, DbType = "UniqueIdentifier NOT NULL", IsPrimaryKey = true, IsDbGenerated = true, UpdateCheck = UpdateCheck.Never)] [DataMember(Order = 1)] public System.Guid ID { get { return this._ID; } set { if ((this._ID != value)) { this.OnIDChanging(value); this.SendPropertyChanging(); this._ID = value; this.SendPropertyChanged("ID"); this.OnIDChanged(); } } } When I compile the code VS warns me that Warning 1 'User.ID' hides inherited member 'Entity.ID'. To make the current member override that mplementation, add the override keyword. Otherwise add the new keyword. That warning is obvious and I have to change the code generated by L2S designer (DataModel.designer.cs) to […] public override System.Guid ID { … protected set … } And the code compiled with no error or warning and everyone is happy. But that is not the end of story. As soon as I made changes to entities of the diagram (dbml) or even I open dbml file to view it, any change manually I made to designer has been vanished and POOF! Redo AGAIN. That is a painful job. Now I wonder if there is a way to force L2S designer not changing portions of auto-generated code. I’ll be appreciated if someone kindly helps me with this issue.

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• PDCurses TUI with C++ Win32 console application

  - by Bach

  I have downloaded pdcurses source and was able to successfully include curses.h in my project, linked the pre-compiled library and all good. After few hours of trying out the library, I saw the tuidemo.c in the demos folder, compiled it into an executable and brilliant! exactly what I needed for my project. Now the problem is that it's a C code, and I am working on a C++ project in VS c++ 2008. The files I need are tui.c and tui.h How can I include that C file in my C++ code? I saw few suggestions here but the compiler was not too happy with 100's of warnings and errors. How can I go on including/using that TUI pdcurses includes!? Thanks EDIT: I added extern "C" statement, so my test looks like this now, but I'm getting some other type of error #include <stdio.h> #include <stdlib.h> using namespace std; extern "C" { #include <tui.h> } void sub0(void) { //do nothing } void sub1(void) { //do nothing } int main (int argc, char * const argv[]) { menu MainMenu[] = { { "Asub", sub0, "Go inside first submenu" }, { "Bsub", sub1, "Go inside second submenu" }, { "", (FUNC)0, "" } /* always add this as the last item! */ }; startmenu(MainMenu, "TUI - 'textual user interface' demonstration program"); return 0; } Although it is compiling successfully, it is throwing an Error at runtime: 0xC0000005: Access violation reading location 0x021c52f9 at line startmenu(MainMenu, "TUI - 'textual user interface' demonstration program"); Not sure where to go from here. thanks again.

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• How to manage multiple python versions ?

  - by Gyom

  short version: how can I get rid of the multiple-versions-of-python nightmare ? long version: over the years, I've used several versions of python, and what is worse, several extensions to python (e.g. pygame, pylab, wxPython...). Each time it was on a different setup, with different OSes, sometimes different architectures (like my old PowerPC mac). Nowadays I'm using a mac (OSX 10.6 on x86-64) and it's a dependency nightmare each time I want to revive script older than a few months. Python itself already comes in three different flavours in /usr/bin (2.5, 2.6, 3.1), but I had to install 2.4 from macports for pygame, something else (cannot remember what) forced me to install all three others from macports as well, so at the end of the day I'm the happy owner of seven (!) instances of python on my system. But that's not the problem, the problem is, none of them has the right (i.e. same set of) libraries installed, some of them are 32bits, some 64bits, and now I'm pretty much lost. For example right now I'm trying to run a three-year-old script (not written by me) which used to use matplotlib/numpy to draw a real-time plot within a rectangle of a wxwidgets window. But I'm failing miserably: py26-wxpython from macports won't install, stock python has wxwidgets included but also has some conflict between 32 bits and 64 bits, and it doesn't have numpy... what a mess ! Obviously, I'm doing things the wrong way. How do you usally cope with all that chaos ?e

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• Should I persist images on EBS or S3?

  - by javanes

  I am migrating my Java,Tomcat, Mysql server to AWS EC2. I have already attached EBS volume for storing MySql data. In my web application people may upload images. So I should persist them. There are 2 alternatives in my mind: Save uploaded images to EBS volume. Use the S3 service. The followings are my notes, please be skeptic about them, as my expertise is not on servers, but software development. EBS plus: S3 storage is more expensive. (0.15 $/Gb 0.1$/Gb) S3 plus: Serving statics from EBS may influence my web server's performance negatively. Is this true? Does Serving images affect server performance notably? For S3 my server will not be responsible for serving statics. S3 plus: Serving statics from EBS may result I/O cost, probably it will be minor. EBS plus: People say EBS is faster. S3 plus: People say S3 is more safe for persistence. EBS plus: No need to learn API, it is straight forward to save the images to EBS volume. Namely I can not decide, will be happy if you guide. Thanks

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• Cheapest way to to determine if a MySQL connection is still alive

  - by MtnViewMark

  I have a pool of MySQL connections for a web-based data service. When it starts to service a request, it takes a connection from the pool to use. The problem is that if there has been a significant pause since that particular connection has been used, the server may have timed it out and closed its end. I'd like to be able to detect this in the pool management code. The trick is this: The environment in which I'm coding gives me only a very abstact API into the connection. I can basically only execute SQL statements. I don't have access to the actual socket or direct access to the MySQL client API. So, the question is: What is the cheapest MySQL statement I can execute on the connection to determine if it is working. For example SELECT 1; should work, but I'm wondering if there is something even cheaper? Perhaps something that doesn't even got across the wire, but is handled in the MySQL client lib and effectively answers the same question?

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• Automatic tracking algorithm

  - by nico

  Hi everyone, I'm trying to write a simple tracking routine to track some points on a movie. Essentially I have a series of 100-frames-long movies, showing some bright spots on dark background. I have ~100-150 spots per frame, and they move over the course of the movie. I would like to track them, so I'm looking for some efficient (but possibly not overkilling to implement) routine to do that. A few more infos: the spots are a few (es. 5x5) pixels in size the movement are not big. A spot generally does not move more than 5-10 pixels from its original position. The movements are generally smooth. the "shape" of these spots is generally fixed, they don't grow or shrink BUT they become less bright as the movie progresses. the spots don't move in a particular direction. They can move right and then left and then right again the user will select a region around each spot and then this region will be tracked, so I do not need to automatically find the points. As the videos are b/w, I though I should rely on brigthness. For instance I thought I could move around the region and calculate the correlation of the region's area in the previous frame with that in the various positions in the next frame. I understand that this is a quite naïve solution, but do you think it may work? Does anyone know specific algorithms that do this? It doesn't need to be superfast, as long as it is accurate I'm happy. Thank you nico

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• Hibernate database integrity with multiple java applications

  - by Austen

  We have 2 java web apps both are read/write and 3 standalone java read/write applications (one loads questions via email, one processes an xml feed, one sends email to subscribers) all use hibernate and share a common code base. The problem we have recently come across is that questions loaded via email sometimes overwrite questions created in one of the web apps. We originally thought this to be a caching issue. We've tried turning off the second level cache, but this doesn't make a difference. We are not explicitly opening and closing sessions, but rather let hibernate manage them via Util.getSessionFactory().getCurrentSession(), which thinking about it, may actually be the issue. We'd rather not setup a clustered 2nd level cache at this stage as this creates another layer of complexity and we're more than happy with the level of performance we get from the app as a whole. So does implementing a open-session-in-view pattern in the web apps and manually managing the sessions in the standalone apps sound like it would fix this? Or any other suggestions/ideas please? <property name="hibernate.transaction.factory_class">org.hibernate.transaction.JDBCTransactionFactory</property> <property name="hibernate.current_session_context_class">thread</property> <property name="hibernate.cache.use_second_level_cache">false</property>

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• Non-wiki CMS for an online user guide

  - by Russell Leggett

  For a large web application I'm building, I need to create an extensive user guide. The first thought was a wiki, but what I've seen lacks the ease of customization I've seen in CMSs, and has a lot of extra features I don't need. The number of users editing the document is small and closed, but it needs to be editable by non-technical users. The number of pages will likely be between 50-100. It also needs to be searchable. It would also be a plus if it had nice readable urls to link to from our web app. Right now, my best guess is WordPress, but that seems a lot more geared towards blogging with just a handful of pages, than having several pages, and possibly no blogs. There isn't a language requirement, although we have the most experience with Java and PHP. We aren't looking to have to do any major coding other than customizing for visuals, so hopefully the language will not be too important. Again, I'm not looking for the best general purpose CMS, just something that would be easiest for a user guide.

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• How to deal with "partial" dates (2010-00-00) from MySQL in Django?

  - by Etienne

  In one of my Django projects that use MySQL as the database, I need to have a date fields that accept also "partial" dates like only year (YYYY) and year and month (YYYY-MM) plus normal date (YYYY-MM-DD). The date field in MySQL can deal with that by accepting 00 for the month and the day. So 2010-00-00 is valid in MySQL and it represent 2010. Same thing for 2010-05-00 that represent May 2010. So I started to create a PartialDateField to support this feature. But I hit a wall because, by default, and Django use the default, MySQLdb, the python driver to MySQL, return a datetime.date object for a date field AND datetime.date() support only real date. So it's possible to modify the converter for the date field used by MySQLdb and return only a string in this format 'YYYY-MM-DD'. Unfortunately the converter use by MySQLdb is set at the connection level so it's use for all MySQL date fields. But Django DateField rely on the fact that the database return a datetime.date object, so if I change the converter to return a string, Django is not happy at all. Someone have an idea or advice to solve this problem? How to create a PartialDateField in Django ? EDIT Also I should add that I already thought of 2 solutions, create 3 integer fields for year, month and day (as mention by Alison R.) or use a varchar field to keep date as string in this format YYYY-MM-DD. But in both solutions, if I'm not wrong, I will loose the special properties of a date field like doing query of this kind on them: Get all entries after this date. I can probably re-implement this functionality on the client side but that will not be a valid solution in my case because the database can be query from other systems (mysql client, MS Access, etc.)

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