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• Anyone Know a Great Sparse One Dimensional Array Library in Python?

  - by TheJacobTaylor

  I am working on an algorithm in Python that uses arrays heavily. The arrays are typically sparse and are read from and written to constantly. I am currently using relatively large native arrays and the performance is good but the memory usage is high (as expected). I would like to be able to have the array implementation not waste space for values that are not used and allow an index offset other than zero. As an example, if my numbers start at 1,000,000 I would like to be able to index my array starting at 1,000,000 and not be required to waste memory with a million unused values. Array reads and writes needs to be fast. Expanding into new territory can be a small delay but reads and writes should be O(1) if possible. Does anybody know of a library that can do it? Thanks!

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• Writing custom Django form fields and widgets

  - by hekevintran

  Django has very good documentation that describes how to write custom database fields and custom template tags and filters. I cannot find the document that describes how to write custom form fields and widgets. Does this document exist? The way I've been able to write custom form fields and widgets is by reading the Django source code and imitating what I see there. I know that there are still things about implementing fields and widgets that I do not completely understand because I have not read any high level document that describes their interfaces.

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• iPhone - Drawing 2D with OpenGL ES, fast and simple.

  - by Johannes Jensen

  I'm going to make a game for the iPhone, and I'm mostly going to be using images. I've read that using Quartz only is slow for actual games with high frame rates, so I was wondering if you guys had any good ideas for using OpenGL for rendering a game scene? I'm going to be using a lot of images, and I want to be able to freely rotate them. I've looked at Apple's examples GLSprite and GLPaint, but I don't really see anything I could use. All I want to do is be able to render images at specific positions, and want to be able to rotate them. I'm a noob at OpenGL, but I know Quartz.

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• How can I avoid "Your system is running low on virtual memory" pop-up?

  - by Xavier Nodet

  Our application sometimes uses a lot of memory, and this is expected. But when we test it under high load on Windows XP, we usually get the very annoying "Your system is running low on virtual memory" popup, and this prevents our automated, unattended, tests to run through... Is it possible to prevent this popup to appear, and just have the allocation fail? The app will handle it gracefully, and tests will go on... We are using Windows XP, but if a solution only exists on later versions, I'd be happy to know anyway.

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• VitrtualStringTree. How to Drag'n'Drop to ROOT level?

  - by Alexandr

  A have a tree: ROOT - VirtualStringTree(You don't see it, TVirtualStringTree.RootNode) - My Root Node 1 - My Root Node 2 - - Second node 1 - - Second node 2 - - Second node 3 - My Root Node 3 I can Drag'n'Drop "My Root Node 3" to any visible node, but I can't return it to defaut position, to the root level of tree. I try that: //Part of code from OnDragDrop Event of VirtualStringTree if (Sender.DropTargetNode = Sender.RootNode) then begin for i := 0 to high(Nodes) do begin LinksTree.MoveTo(Nodes[i], Sender.DropTargetNode, Attachmode, False); end; end; I places mouse to nowhere, but nothing happens. In DragOver I accepted drop to root if DropTarget is VST.RootNode. Anybody knows, how to drop node to VST.RootNode if I drag mouse to empty space of component?

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• In a virtual machine monitor such as VMware's ESXi Server, how are shadow page tables implemented?

  - by ali01

  My understanding is that VMMs such as VMware's ESXi Server maintain shadow page tables to map virtual page addresses of guest operating systems directly to machine (hardware) addresses. I've been told that shadow page tables are then used directly by the processor's paging hardware to allow memory access in the VM to execute without translation overhead. I would like to understand a bit more about how the shadow page table mechanism works in a VMM. Is my high level understanding above correct? What kind of data structures are used in the implementation of shadow page tables? What is the flow of control from the guest operating system all the way to the hardware? How are memory access translations made for a guest operating system before its shadow page table is populated? How is page sharing supported? Short of straight up reading the source code of an open source VMM, what resources can I look into to learn more about hardware virtualization?

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• What is the best method of assessment for computer science students?

  - by Gavimoss

  This question is a bit more philosophical so feel free to remove if you like but it's been bugging me for the last 4 years! As a final year student I find that exams can be often be passed with a couple of days of cramming, without necessarily retaining or understanding the content i.e. a regurgitation of lecture notes is often enough to gain high marks. A friend of mine is about to graduate with an honours degree whose final year evaluation was based solely on practical work (a project, assignment marks and the creation of a poster) yet all of this work could have been completed by a third party. Personally I don't think either of these methods of assessment is sufficient as I am currently on track for a 1st class honours in artificial intelligence and computer science and believe this is mostly due to my skill in passing exams not my skill as a programmer or my vast in depth knowledge of any of the subjects I have "studied". Surely there is a better way to assess our skills - isn't there?

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• How to check if EditText has a value in Android / Java

  - by Allen Gingrich

  This should be simple, but I have tried if statements checking for null values and also ones checking the .length of it: EditText marketValLow = (EditText) findViewById(R.id.marketValLow); EditText marketValHigh = (EditText) findViewById(R.id.marketValHigh); if (marketValLow.getText().length() != 0 && marketValHigh.getText().length() != 0) { Intent intent = new Intent(); intent.setClass(v.getContext(), CurrentlyOwe.class); startActivity(intent); } else { Toast.makeText(CurrentMarketValue.this, "You need to enter a high AND low.", Toast.LENGTH_SHORT); } But it doesn't detect nothing was entered. Any ideas? Thanks!

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• Question about varrying top margin when using custom Fonts on the iPhone.

  - by user170030

  I am using FontLabel to display varying lengths of texts in a custom font. I size the FontLabel using the following : CGSize size = [myString sizeWithFont:[UIFont systemFontOfSize:[[[UIApplication sharedApplication] delegate] getFontSize]] constrainedToSize:CGSizeMake(290, 4000) lineBreakMode:UILineBreakModeWordWrap]; For some reason, this always presents a Fontlabel where the text starts at a different space from the top. Sometimes the text begins at the correct location. Other times, it appears either too high or too low. Would appreciate some help in how to solve this issue.

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• Sorting and aligning the contents of a text file in Python

  - by Emily Price

  In my program I have a text file that I read from and write to. However, I would like to display the contents of the text file in an aligned and sorted manner. The contents currently read: name, score name, score This is my code where the text file in read and printed: elif userCommand == 'V': print "High Scores:" scoresFile = open("scores1.txt", 'r') scores = scoresFile.read().split("\n") for score in scores: print score scoresFile.close() Would I have to convert this information into lists in order to be able to do this? If so, how do I go about doing this? Thank you

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• Best way to code a webservice in weblogic?

  - by John

  I am new to Weblogic and J2ee. I need to build a webservice that simply runs a query on the backend database (DB2 zOS) and returns the results. Being new to this I have a few questions. 1) What is the best way to build the webservice? 2) How do I connect to the database with weblogic. 3) Is there a way to cache the data returned so that the next request for the same data is pulled from cache? If googled for this but there seems to be many way to handle this. I am looking for the best way that can handle a high volume of requests. Any links to sample code would be helpful. - Thanks

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• Ways to make your WCF services compatible with non-.NET consumers

  - by Mayo

  I'm working on adding a WCF services layer to my existing .NET application. This layer will be hosted in IIS and will be consumed by a variety of UIs, at least one of which will not use Microsoft technologies. I can make a Web service in WCF that is consumed by my .NET application. However, I'm concerned about things that work in the .NET world but not with other technologies. For example, simply throwing an exception from my WCF service works fine in .NET. But according to this article, one should approach exception handling with fault contracts to ensure compatibility with non-.NET consumers. The author labels this lack of foresight as The Fallacy of the .NET-Only World. Does anyone have any high level suggestions or links to articles that cover interoperability between WCF and non-.NET consumers? I realize I'm potentially working against the YAGNI principle. I'm only really looking to avoid things that will be incredibly difficult to overcome later when the developers of the non-.NET consumer report problems to me.

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• How do I keep JTextFields in a Java Swing BoxLayout from expanding?

  - by Matthew

  I have a JPanel that looks something like this: JPanel panel = new JPanel(); panel.setLayout(new BoxLayout(panel, BoxLayout.Y_AXIS)); ... panel.add (jTextField1); panel.add (Box.createVerticalStrut(10)); panel.add (jButton1); panel.add (Box.createVerticalStrut(30)); panel.add (jTextField2); panel.add (Box.createVerticalStrut(10)); panel.add (jButton2); ... //etc. My problem is that the JTextFields become huge vertically. I want them to only be high enough for a single line, since that is all that the user can type in them. The buttons are fine (they don't expand vertically). Is there any way to keep the JTextFields from expanding? I'm pretty new to Swing, so let me know if I'm doing everything horribly wrong.

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• Are there any good books on writing commercial quality software?

  - by Andy

  Hey, My background has been generally new technology demonstrators, which, well... demonstrate the latest technology and how it can be of use to a clients company. They use it for internal demos etc. Now my career has shiffed course a bit more into actual products, in particular software which runs in locations like museums as interactive pieces. Clearly, although the technology demonstrators had to be well coded etc, there wasn't as much emphasis as there is on my current work, which has to work, be highly configurable, probably multi-ligual and run constantly, without restarts. So my question is, now that I'm trying to up my coding quality and write more commercial applications, are there any books which discuss issues surrounding high quality commercial software? I currently have a copy of Code Complete 2nd Edition, which is excellent, but just wondering if there's any better, possibly more focused titles out there? Thanks a lot! Andy.

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• What strategies are efficient to handle concurrent reads on heterogeneous multi-core architectures?

  - by fabrizioM

  I am tackling the challenge of using both the capabilities of a 8 core machine and a high-end GPU (Tesla 10). I have one big input file, one thread for each core, and one for the the GPU handling. The Gpu thread, to be efficient, needs a big number of lines from the input, while the Cpu thread needs only one line to proceed (storing multiple lines in a temp buffer was slower). The file doesn't need to be read sequentially. I am using boost. My strategy is to have a mutex on the input stream and each thread locks - unlocks it. This is not optimal because the gpu thread should have a higher precedence when locking the mutex, being the fastest and the most demanding one. I can come up with different solutions but before rush into implementation I would like to have some guidelines. What approach do you use / recommend ?

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• SQL Function for On Balance Volume (Financial Query)

  - by CraigJSte

  I would like to create a function for On Balance Volume (SQL Function). This is too complex of a calculation for met to figure out but here is the outline of the User Defined Table Function. If someone could help me to fill in the blanks I would appreciate it. Craig CREATE FUNCTION [dbo].[GetStdDev3] (@TKR VARCHAR(10)) RETURNS @results TABLE ( dayno SMALLINT IDENTITY(1,1) PRIMARY KEY , [date] DATETIME , [obv] FLOAT ) AS BEGIN DECLARE @rowcount SMALLINT INSERT @results ([date], [obv]) // CREATE A FUNCTION FOR ON BALANCE VOLUME // On Balance Volume is the Summ of Volume for Total Periods // OBV = 1000 at Period = 0 // OBV = OBV Previous + Previous Volume if Close Previous Close // OBV = OBV Previous - Previous Volume if Close < Previous Close // OBV = OBV Previous if Close = Previous Close // The actual Value of OBV is not important so to keep the ratio low we reduce the // Total Value of Tickers by 1/10th or 1/100th // For Value of Volume = Volume * .01 if Volume < 999 // For Value of Volume = Volume * .001 If Volume = 999 FROM Tickers RETURN END This is the Tickers table [dbo].[Tickers]( [ticker] [varchar](10) NULL, [date] [datetime] NULL, [high] [float] NULL, [low] [float] NULL, [open] [float] NULL, [close] [float] NULL, [volume] [float] NULL, [time] [datetime] NULL, [change] [float] NULL )

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• Add widgets to custom WordPress sidebars on theme activation?

  - by McGirl

  I'm working on a WordPress 3.0 multi-site installation. Each new blog will use the same theme with slight modifications (a custom Thesis install, if it matters). I'm trying to automate the set-up process for each new blog as much as possible. To that end, I'd like to automatically add widgets to my custom sidebars and widget-enabled footers. It'd be even better if the widgets could have pre-set parameters/content, that I or the blog owner could then go into the Widgets panel and edit. I've searched high and low and haven't been able to figure out a way to make this work. Any and all suggestions are welcome. Thanks so much!

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• Waiting for a background operation to complete

  - by JohnHenry

  I have been suffering from the all too common 'Waiting for a background operation to complete...' message in Visual Studio 2012 (Professional) for a while now but it has been fairly sporadic. Lately though, I am really struggling to use Visual Studio as pretty much whenever i try and do anything with any Razor views (mostly clicking to move the cursor) visual studio hangs and the above message appears for about a minute at a time. (If when its finished doing stuff i then click in the view again, the process repeats, and repeats, and repeats.....) I have searched high and low, and read loads of articles regarding this and peoples suggestions and tried changing indentation settings, resetting settings, etc but none have worked. Has anyone come across something else that may work as this is seriously impeding my ability to use visual studio and sadly provoking much cursing.

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• Can I tell Borland C++ Builder to copy a file somewhere else after it is built?

  - by MrVimes

  I have two computers. One is intended to be left 'free' for high-performance activities (such as playing games) The other is my 'all purpose' computer where I install all the apps I use for creating things, and so on. On the second computer I use Codegear C++ Builder to work on an app that I use on the first computer. If I have BCB compile to comp 1 it is hopeless. It becomes unresponsive. It compiles locally very quickly. So what I do is compile locally and then copy the exe to the other machine. Well, I'm all for streamlining processes, so I want a way to compile on PC2 and use on PC1 without any intermediate steps. So is it possible to have BCB do the compiling on PC2 and create a local exe file, then copy the file to PC 1?

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• How to change password hashing algorithm when using spring security?

  - by harry

  I'm working on a legacy Spring MVC based web Application which is using a - by current standards - inappropriate hashing algorithm. Now I want to gradually migrate all hashes to bcrypt. My high level strategy is: New hashes are generated with bcrypt by default When a user successfully logs in and has still a legacy hash, the app replaces the old hash with a new bcrypt hash. What is the most idiomatic way of implementing this strategy with Spring Security? Should I use a custom Filter or my on AccessDecisionManager or …?

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• cross domain gwt ?

  - by jlo

  is there a way to run gwt on a proxy loaded web page ? ex) using proxy script on myexamplesite.com that loads finance.google.com, and running GWT on the newly loaded page. I've been doing the above before I found about GWT, using LAMP stack + Jquery (UI), which quickly turned out to be crap and inefficient. All this trouble to bypass browser's default Single Origin Policy. So, right now, is it possible to overcome this problem with GWT ? Is it possible to some how, run javascript on a html page from finance.google.com loaded into myexamplesite.com's frame with GWT or other solution? I am not looking to do JSON or RSS related topics. What I need is high lighted in bold. Is GWT + Gears what I should be using ? Thank you.

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• Switching from C++ (with a lot of STL use) to C for interpreter building

  - by wndsr

  I'm switching from C++ to C because I'm rebuilding my toy interpreter. I was used to vectors for dynamic allocation of objects like tokens or instructions of my programs, stacks and mainly strings with all their aspects. Now, in C I'm not going to have all these anymore. I know that I will have to use a lot of memory management, too. I'm completely new to C, I only know the high-level easy-life data structures from the STL, how can I get started with strings and dynamic memory allocation?

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• Hibernate / MySQL Bulk insert problem

  - by Marty Pitt

  I'm having trouble getting Hibernate to perform a bulk insert on MySQL. I'm using Hibernate 3.3 and MySQL 5.1 At a high level, this is what's happening: @Transactional public Set<Long> doUpdate(Project project, IRepository externalSource) { List<IEntity> entities = externalSource.loadEntites(); buildEntities(entities, project); persistEntities(project); } public void persistEntities(Project project) { projectDAO.update(project); } This results in n log entries (1 for every row) as follows: Hibernate: insert into ProjectEntity (name, parent_id, path, project_id, state, type) values (?, ?, ?, ?, ?, ?) I'd like to see this get batched, so the update is more performant. It's possible that this routine could result in tens-of-thousands of rows generated, and a db trip per row is a killer. Why isn't this getting batched? (It's my understanding that batch inserts are supposed to be default where appropriate by hibernate).

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• Best and safest Java Profiler for production use?

  - by Pete

  I'm looking for a Java Profiler for use in a very high demand production environment, either commercial or free, that meets all of the following requirements: Lightweight integration with code (no recompile with special options, no code hooks, etc). Dropping some profiler specific .jars alongside the application code is ok. Should be able to connect/disconnect to the JVM without restarting the application. When profiling is not active, no impact to performance When profiling is active, negligible impact to performance. Very slight degradation is acceptable. Must do all the 'expected' stuff a profiler does - time spent in each method to find hotspots, object allocation/memory profiling, etc. Essentially I need something that can sit dormant in production when everything is fine without anyone knowing or caring that it is there, but then be able to connect to it hassle (and performance degradation) free to pinpoint the hard to find problems like hotspots and synchronization issues.

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• Faster way to compare two sets of points in N-dimensional space?

  - by Amit

  List1 contains a high number (~7^10) of N-dimensional points (N <=10), List2 contains the same or fewer number of N-dimensional points (N <=10). My task is this: I want to check which point in List2 is closest (euclidean distance) to a point in List1 for every point in List1 and subsequently perform some operation on it. I have been doing it the simple- the nested loop way when I didn't have more than 50 points in List1, but with 7^10 points, this obviously takes up a lot of time. What is the fastest way to do this? Any concepts from Computational Geometry might help?

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