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• Searches (and general querying) with HBase and/or Cassandra (best practices?)

  - by alexeypro

  I have User model object with quite few fields (properties, if you wish) in it. Say "firstname", "lastname", "city" and "year-of-birth". Each user also gets "unique id". I want to be able to search by them. How do I do that properly? How to do that at all? My understanding (will work for pretty much any key-value storage -- first goes key, then value) u:123456789 = serialized_json_object ("u" as a simple prefix for user's keys, 123456789 is "unique id"). Now, thinking that I want to be able to search by firstname and lastname, I can save in: f:Steve = u:384734807,u:2398248764,u:23276263 f:Alex = u:12324355,u:121324334 so key is "f" - which is prefix for firstnames, and "Steve" is actual firstname. For "u:Steve" we save as value all user id's who are "Steve's". That makes every search very-very easy. Querying by few fields (properties) -- say by firstname (i.e. "Steve") and lastname (i.e. "l:Anything") is still easy - first get list of user ids from "f:Steve", then list from "l:Anything", find crossing user ids, an here you go. Problems (and there are quite a few): Saving, updating, deleting user is a pain. It has to be atomic and consistent operation. Also, if we have size of value limited to some value - then we are in (potential) trouble. And really not of an answer here. Only zipping the list of user ids? Not too cool, though. What id we want to add new field to search by. Eventually. Say by "city". We certainly can do the same way "c:Los Angeles" = ..., "c:Chicago" = ..., but if we didn't foresee all those "search choices" from the very beginning, then we will have to be able to create some night job or something to go by all existing User records and update those "c:CITY" for them... Quite a big job! Problems with locking. User "u:123" updates his name "Alex", and user "u:456" updates his name "Alex". They both have to update "f:Alex" with their id's. That means either we get into overwriting problem, or one update will wait for another (and imaging if there are many of them?!). What's the best way of doing that? Keeping in mind that I want to search by many fields? P.S. Please, the question is about HBase/Cassandra/NoSQL/Key-Value storages. Please please - no advices to use MySQL and "read about" SELECTs; and worry about scaling problems "later". There is a reason why I asked MY question exactly the way I did. :-)

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• Creating a music catalog in C# and extracting first 30 seconds as soon as the first words are sung

  - by Rad

  I already read a question: Separation of singing voice from music. I don’t need this complex audio processing. I only need some detection mechanism that would detect that there is some voice/vocal playing while the music is playing (or not playing) I need to extract first 30 seconds when a vocalist starts singing along with full band music. See question 2 below. I want to create a music catalog using ASP.NET MVC 2 and Silverlight clients and C#.NET 4.0 programming language that would be front store. On the backend I would also like to create a desktop WPF/Windows application to create the music catalog from already existing music files, most of which have metadata in them ID3v1, ID3v2.3, ID3v2.4, iTunes MP4, WMA, Vorbis Comments and APE Tags etc. I would possibly like to create a web service that would allow catalog contributors to upload a zipped album and trigger metadata extraction of music data and extraction of music segments as described below. I would be happy if I achieve no. 1 below. Let's say I have 1000ths of songs in mp3 (or other formats) grouped in subfolders using some classification (Genre, Artists, Albums, Composers or other groupings). I want to create tables in DB that would organize songs so they can be searched based on different criteria (year, length, above classification or by song title, description etc) like what iTune store allows to their customers. I want to extract metadata from various formats (I will try to get songs in mp3 format, but there may be other popular formats) and allow music Catalog manager person to add missing data from either desktop or web applications. He or other contributors can upload zipped music via an HTML or Silverlight upload or WPF. Can anybody suggest open source libraries, articles, code snippets that can do that in an automatic way using .NET and possibly SQL Server DB? My main questions are these. This is an audio processing challenge. I want to extract 2 segments of music (questions 1 and 2): 1. How to extract a music segment: 1-2 seconds before a vocal starts singing and up to 30 seconds from that point in time and 2. Much more challenging is to find repeating segments (One would usually find or recognize the names of the songs and songs are usually known by these refrains. How would I go about creating a list of songs that go great together like what Genius from iTune does? Is there any characteristics of music that can be used to match songs? The goal is for people quickly scan and recognize songs i.e. associate melody, words with a title/album so they can make intelligent decisions like buying a song, create similar mood songs. Thanks, Rad

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• SaaS Architecture Question from Newbie

  - by user226767

  I have developed a number of departmental client-server applications, and am now ready to begin working on moving one of these applications to a SaaS model. I have done some basic web development, but I'm a newbie when it comes to SaaS architectures. One of the first questions that comes to mind as I try to design the architecture is the question of single vs. multi tenancy. The pros and cons of each vary significantly depending on the type of application and scale required, so I'd like to describe my application and scale needs below, and hope others can comment on how I should get started with the architecture. The client-server application currently consists of a Firebird database and a Windows application. The database contains about 20 tables containing a few thousand records in 4 primary tables, and a few hundred records in various lookup and related tables. Although the number of records is small, the size can get large, as the database can contain large BLOBS. Each customer sets up their own database and has a handful of users within the organization connected to it. When I update the db schema, a new windows application is released, and it checks the db schema and then applies the updates as needed. For the SaaS application, I am designing for 100's (not 1000's or millions) of new customers per year. My first thought was to go with a multi tenancy model to make updates easy (shut down apply the updates to one database, and then start up). On the other hand, a single tenancy model would provide a means to roll updates out to a group of customers at a time, and spread the risk of data corruption - i.e. if something goes wrong with a database, it will impact one customer instead of all customers. With this idea, I was thinking of having a single web front-end which would connect to a single customer database upon login. Thus, when a new customer creates an account, a new database would be created (each customer would have their own db with multiple users as needed for the customer). In this model, a db update would require either a process to go through each db to apply schema changes, or a trigger upon logging in to initiate a schema update similar to the client-server model currently in use. Can anyone point me to information for similar applications which have been ported from client-server to SaaS? Or provide any pointers to consider? Basically I'm looking for architecture examples of taking a departmental application and making it available as a self service website for multiple customers. Thanks for any suggestions, resources, etc.

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• Update time descriptions every minute using jquery/javascript

  - by Amy Neville

  I have created the following code to update the text contents of all spans like this every minute. There are numerous of these spans on the page which all need to be updated every minute: <span unix="1372263005" class="time_ago">4 minutes ago</span> The code is as follows: window.setInterval(function(){ var unix = $(".time_ago").text(); var now = new Date().getTime(); var amount = 0; var difference = 0; difference = now - parseInt(unix); if (difference < 60) { $(".time_ago").text('<span unix="' + unix + '" class="time_ago">a few seconds ago</span>'); } else if (difference < 120) { $(".time_ago").text('<span unix="' + unix + '" class="time_ago">a minute ago</span>'); } else if (difference < 3600) { amount = floor(difference / 60); $(".time_ago").text('<span unix="' + unix + '" class="time_ago">' + amount + ' minutes ago</span>'); } else if (difference < 7200) { $(".time_ago").text('<span unix="' + unix + '" class="time_ago">an hour ago</span>'); } else if (difference < 86400) { amount = floor(difference / 3600); $(".time_ago").text('<span unix="' + unix + '" class="time_ago">' + amount + ' hours ago</span>'); } else if (difference < 172800) { $(".time_ago").text('<span unix="' + unix + '" class="time_ago">a day ago</span>'); } else if (difference < 2635200) { amount = floor(difference / 86400); $(".time_ago").text('<span unix="' + unix + '" class="time_ago">' + amount + ' days ago</span>'); } else if (difference < 5270400) { $(".time_ago").text('<span unix="' + unix + '" class="time_ago">a month ago</span>'); } else if (difference < 31622400) { amount = floor(difference / 2635200); $(".time_ago").text('<span unix="' + unix + '" class="time_ago">' + amount + ' months ago</span>'); } else if (difference < 63244800) { $(".time_ago").text('<span unix="' + unix + '" class="time_ago">a year ago</span>'); } else (difference >= 63244800) { amount = floor(difference / 31622400); $(".time_ago").text('<span unix="' + unix + '" class="time_ago">' + amount + ' years ago</span>'); } return false; }, 60); EDIT) Ok, now I have made some changes on your advice but it's changing the span texts to 43351 years. Any ideas why it is doing that?

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• Need help with implementing collision detection using the Separating Axis Theorem

  - by Eddie Ringle

  So, after hours of Googling and reading, I've found that the basic process of detecting a collision using SAT is: for each edge of poly A project A and B onto the normal for this edge if intervals do not overlap, return false end for for each edge of poly B project A and B onto the normal for this edge if intervals do not overlap, return false end for However, as many ways as I try to implement this in code, I just cannot get it to detect the collision. My current code is as follows: for (unsigned int i = 0; i < asteroids.size(); i++) { if (asteroids.valid(i)) { asteroids[i]->Update(); // Player-Asteroid collision detection bool collision = true; SDL_Rect asteroidBox = asteroids[i]->boundingBox; // Bullet-Asteroid collision detection for (unsigned int j = 0; j < player.bullets.size(); j++) { if (player.bullets.valid(j)) { Bullet b = player.bullets[j]; collision = true; if (b.x + (b.w / 2.0f) < asteroidBox.x - (asteroidBox.w / 2.0f)) collision = false; if (b.x - (b.w / 2.0f) > asteroidBox.x + (asteroidBox.w / 2.0f)) collision = false; if (b.y - (b.h / 2.0f) > asteroidBox.y + (asteroidBox.h / 2.0f)) collision = false; if (b.y + (b.h / 2.0f) < asteroidBox.y - (asteroidBox.h / 2.0f)) collision = false; if (collision) { bool realCollision = false; float min1, max1, min2, max2; // Create a list of vertices for the bullet CrissCross::Data::LList<Vector2D *> bullVerts; bullVerts.insert(new Vector2D(b.x - b.w / 2.0f, b.y + b.h / 2.0f)); bullVerts.insert(new Vector2D(b.x - b.w / 2.0f, b.y - b.h / 2.0f)); bullVerts.insert(new Vector2D(b.x + b.w / 2.0f, b.y - b.h / 2.0f)); bullVerts.insert(new Vector2D(b.x + b.w / 2.0f, b.y + b.h / 2.0f)); // Create a list of vectors of the edges of the bullet and the asteroid CrissCross::Data::LList<Vector2D *> bullEdges; CrissCross::Data::LList<Vector2D *> asteroidEdges; for (int k = 0; k < 4; k++) { int n = (k == 3) ? 0 : k + 1; bullEdges.insert(new Vector2D(bullVerts[k]->x - bullVerts[n]->x, bullVerts[k]->y - bullVerts[n]->y)); asteroidEdges.insert(new Vector2D(asteroids[i]->vertices[k]->x - asteroids[i]->vertices[n]->x, asteroids[i]->vertices[k]->y - asteroids[i]->vertices[n]->y)); } for (unsigned int k = 0; k < asteroidEdges.size(); k++) { Vector2D *axis = asteroidEdges[k]->getPerpendicular(); min1 = max1 = axis->dotProduct(asteroids[i]->vertices[0]); for (unsigned int l = 1; l < asteroids[i]->vertices.size(); l++) { float test = axis->dotProduct(asteroids[i]->vertices[l]); min1 = (test < min1) ? test : min1; max1 = (test > max1) ? test : max1; } min2 = max2 = axis->dotProduct(bullVerts[0]); for (unsigned int l = 1; l < bullVerts.size(); l++) { float test = axis->dotProduct(bullVerts[l]); min2 = (test < min2) ? test : min2; max2 = (test > max2) ? test : max2; } delete axis; axis = NULL; if ( (min1 - max2) > 0 || (min2 - max1) > 0 ) { realCollision = false; break; } else { realCollision = true; } } if (realCollision == false) { for (unsigned int k = 0; k < bullEdges.size(); k++) { Vector2D *axis = bullEdges[k]->getPerpendicular(); min1 = max1 = axis->dotProduct(asteroids[i]->vertices[0]); for (unsigned int l = 1; l < asteroids[i]->vertices.size(); l++) { float test = axis->dotProduct(asteroids[i]->vertices[l]); min1 = (test < min1) ? test : min1; max1 = (test > max1) ? test : max1; } min2 = max2 = axis->dotProduct(bullVerts[0]); for (unsigned int l = 1; l < bullVerts.size(); l++) { float test = axis->dotProduct(bullVerts[l]); min2 = (test < min2) ? test : min2; max2 = (test > max2) ? test : max2; } delete axis; axis = NULL; if ( (min1 - max2) > 0 || (min2 - max1) > 0 ) { realCollision = false; break; } else { realCollision = true; } } } if (realCollision) { player.bullets.remove(j); int numAsteroids; float newDegree; srand ( j + asteroidBox.x ); if ( asteroids[i]->degree == 90.0f ) { if ( rand() % 2 == 1 ) { numAsteroids = 3; newDegree = 30.0f; } else { numAsteroids = 2; newDegree = 45.0f; } for ( int k = 0; k < numAsteroids; k++) asteroids.insert(new Asteroid(asteroidBox.x + (10 * k), asteroidBox.y + (10 * k), newDegree)); } delete asteroids[i]; asteroids.remove(i); } while (bullVerts.size()) { delete bullVerts[0]; bullVerts.remove(0); } while (bullEdges.size()) { delete bullEdges[0]; bullEdges.remove(0); } while (asteroidEdges.size()) { delete asteroidEdges[0]; asteroidEdges.remove(0); } } } } } } bullEdges is a list of vectors of the edges of a bullet, asteroidEdges is similar, and bullVerts and asteroids[i].vertices are, obviously, lists of vectors of each vertex for the respective bullet or asteroid. Honestly, I'm not looking for code corrections, just a fresh set of eyes.

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• Alright, I'm still stuck on this homework problem. C++

  - by Josh

  Okay, the past few days I have been trying to get some input on my programs. Well I decided to scrap them for the most part and try again. So once again, I'm in need of help. For the first program I'm trying to fix, it needs to show the sum of SEVEN numbers. Well, I'm trying to change is so that I don't need the mem[##] = ####. I just want the user to be able to input the numbers and the program run from there and go through my switch loop. And have some kind of display..saying like the sum is?.. Here's my code so far. #include <iostream> #include <iomanip> #include <ios> using namespace std; int main() { const int READ = 10; const int WRITE = 11; const int LOAD = 20; const int STORE = 21; const int ADD = 30; const int SUBTRACT = 31; const int DIVIDE = 32; const int MULTIPLY = 33; const int BRANCH = 40; const int BRANCHNEG = 41; const int BRANCHZERO = 42; const int HALT = 43; int mem[100] = {0}; //Making it 100, since simpletron contains a 100 word mem. int operation; //taking the rest of these variables straight out of the book seeing as how they were italisized. int operand; int accum = 0; // the special register is starting at 0 int counter; for ( counter=0; counter < 100; counter++) mem[counter] = 0; // This is for part a, it will take in positive variables in //a sent-controlled loop and compute + print their sum. Variables from example in text. mem[0] = 1009; mem[1] = 1109; mem[2] = 2010; mem[3] = 2111; mem[4] = 2011; mem[5] = 3100; mem[6] = 2113; mem[7] = 1113; mem[8] = 4300; counter = 0; //Makes the variable counter start at 0. while(true) { operand = mem[ counter ]%100; // Finds the op codes from the limit on the mem (100) operation = mem[ counter ]/100; //using a switch loop to set up the loops for the cases switch ( operation ){ case READ: //reads a variable into a word from loc. Enter in -1 to exit cout <<"\n Input a positive variable: "; cin >> mem[ operand ]; counter++; break; case WRITE: // takes a word from location cout << "\n\nThe content at location " << operand << " is " << mem[operand]; counter++; break; case LOAD:// loads accum = mem[ operand ];counter++; break; case STORE: //stores mem[ operand ] = accum;counter++; break; case ADD: //adds accum += mem[operand];counter++; break; case SUBTRACT: // subtracts accum-= mem[ operand ];counter++; break; case DIVIDE: //divides accum /=(mem[ operand ]);counter++; break; case MULTIPLY: // multiplies accum*= mem [ operand ];counter++; break; case BRANCH: // Branches to location counter = operand; break; case BRANCHNEG: //branches if acc. is < 0 if (accum < 0) counter = operand; else counter++; break; case BRANCHZERO: //branches if acc = 0 if (accum == 0) counter = operand; else counter++; break; case HALT: // Program ends break; } } return 0; } part B int main() { const int READ = 10; const int WRITE = 11; const int LOAD = 20; const int STORE = 21; const int ADD = 30; const int SUBTRACT = 31; const int DIVIDE = 32; const int MULTIPLY = 33; const int BRANCH = 40; const int BRANCHNEG = 41; const int BRANCHZERO = 41; const int HALT = 43; int mem[100] = {0}; int operation; int operand; int accum = 0; int pos = 0; int j; mem[22] = 7; // loop 7 times mem[25] = 1; // increment by 1 mem[00] = 4306; mem[01] = 2303; mem[02] = 3402; mem[03] = 6410; mem[04] = 3412; mem[05] = 2111; mem[06] = 2002; mem[07] = 2312; mem[08] = 4210; mem[09] = 2109; mem[10] = 4001; mem[11] = 2015; mem[12] = 3212; mem[13] = 2116; mem[14] = 1101; mem[15] = 1116; mem[16] = 4300; j = 0; while ( true ) { operand = memory[ j ]%100; // Finds the op codes from the limit on the memory (100) operation = memory[ j ]/100; //using a switch loop to set up the loops for the cases switch ( operation ){ case 1: //reads a variable into a word from loc. Enter in -1 to exit cout <<"\n enter #: "; cin >> memory[ operand ]; break; case 2: // takes a word from location cout << "\n\nThe content at location " << operand << "is " << memory[operand]; break; case 3:// loads accum = memory[ operand ]; break; case 4: //stores memory[ operand ] = accum; break; case 5: //adds accum += mem[operand];; break; case 6: // subtracts accum-= memory[ operand ]; break; case 7: //divides accum /=(memory[ operand ]); break; case 8: // multiplies accum*= memory [ operand ]; break; case 9: // Branches to location j = operand; break; case 10: //branches if acc. is < 0 break; case 11: //branches if acc = 0 if (accum == 0) j = operand; break; case 12: // Program ends exit(0); break; } j++; } return 0; }

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• How are you using IronPython?

  - by Will Dean

  I'm keen to drink some modern dynamic language koolaid, so I've believed all the stuff on Michael Foord's blog and podcasts, I've bought his book (and read some of it), and I added an embedded IPy runtime to a large existing app a year or so ago (though that was for someone else and I didn't really use it myself). Now I need to do some fairly simple code generation stuff, where I'm going to call a few methods on a few .net objects (custom, C#-authored objects), create a few strings, write some files, etc. The experience of trying this leaves me feeling like the little boy who thinks he's the only one who can see that The Emperor has no clothes on. If you're using IronPython, I'd really appreciate knowing how you deal with the following aspects of it: Code editing - do you use the .NET framework without Intellisense? Refactoring - I know a load of 'refactoring' is about working around language-related busywork, so if Python is sufficiently lightweight then we won't need that, But things like renames seem to me to be essential to iteratively developing quality code regardless of language. Crippling startup time - One of the things which is supposed to be good about interpreted languages is the lack of compile time leading to fast interactive development. Unfortunately I can compile a C# application and launch it quicker than IPy can start up. Interactive hacking - the IPy console/repl is supposed to be good for this, but I haven't found a good way to take the code you've interactively arrived at and persist it into a file - cut and paste from the console is fairly miserable. And the console seems to hold references to .NET assemblies you've imported, so you have to quit it and restart it if you're working on the C# stuff as well. Hacking on C# in something like LinqPad seems a much faster and easier way to try things out (and has proper Intellisense). Do you use the console? Debugging - what's the story here? I know someone on the IPy team is working on a command-line hobby-project, but let's just say I'm not immediately attracted to a command line debugger. I don't really need a debugger from little Python scripts, but I would if I were to use IPy for scripting unit tests, for example. Unit testing - I can see that dynamic languages could be great for this, but is there any IDE test-runner integration (like for Resharper, etc). The Foord book has a chapter about this, which I'll admit I have not yet read properly, but it does seem to involve driving a console-mode test-runner from the command prompt, which feels to be an enormous step back from using an integrated test runner like TestDriven.net or Resharper. I really want to believe in this stuff, so I am still working on the assumption that I've missed something. I would really like to know how other people are dealing with IPy, particularly if they're doing it in a way which doesn't feel like we've just lost 15 years'-worth of tool development.

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• Arguments for moving from LINQtoSQL to Nhibernate?

  - by sah302

  Backstory: Hi all, I just spent a lot of time reading many of the LINQ vs Nhibernate threads here and on other sites. I work in a small development team of 4 people and we don't even have really any super experienced developers. We work for a small company that has a lot of technical needs but not enough developers to implement them (and hiring more is out of the question right now). Typically our projects (which individually are fairly small) have been coded separately and weren't really layered in anyway, code wasn't re-used, no class libraries, and we just use the LINQtoSQL .dbml files for our pojects, we really don't even use objects but pass around values and stuff, the only time we use objects is when inserting to a database (heck not even querying since you don't need to assign it to a type and can just bind to gridview). Despite all this as I said our company has a lot of technical needs, no one could come to us for a year and we would have plenty of work to implement requested features. Well I have decided to change that a bit first by creating class libraries and actually adding layers to our applications. I am trying to meet these guys halfway by still using LINQtoSQL as the ORM yet and still use VB as the language. However I am finding it a b***h of a time dealing with so many thing in LINQtoSQL that I found easy in Nhibernate (automatic handling of the session, criteria creation easier than expression trees, generic an dynamic querying easier etc.) So... Question: How can I convince my lead developers and other senior programmers that switching to Nhibernate is a good thing? That being in control of our domain objects is a good thing? That being able to implement interfaces is a good? I've tried exlpaining the advantages of this before but it's not understood by them because they've never programmed in a true OO & layered way. Also one of the counter arguments to this I can see is sqlMetal generates those classes automatically and therefore it saves a lot of time. I can't really counter that other than saying spending more time on infrastructure to make it more scalable and flexible is good, but they can't see how. Again, I know the features and advantages (somewhat enough I believe) of each, but I need arguments applicable to my context, hence why I provided the context. I just am not a very good arguer I guess. (Caveat: For all the LINQtoSQL lovers, I may just not be super proficient as LINQ, but I find it very cumbersome that you are required to download some extra library for dynamic queries which don't by default support guid comparisons, and I also find the way of updating entitites to be cumbersome as well in terms of data context managing, so it could just be that I suck hehe.)

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• Why is cell phone software still so primitive?

  - by Tomislav Nakic-Alfirevic

  I don't do mobile development, but it strikes me as odd that features like this aren't available by default on most phones: full text search: searches all address book contents, messages, anything else being a plus better call management: e.g. a rotating audio call log, meaning you always have the last N calls recorded for your listening pleasure later (your little girl just said her first "da-da" while you were on a business trip, you had a telephone job interview, you received complex instructions to do something etc.) bluetooth remote control (like e.g. anyRemote, but available by default on a bluetooth phone) no multitasking capabilities worth mentioning and in general no e.g. weekly software updates, making the phone much more usable (even if it had to be done over USB, rather than over the network). I'm sure I was dumbfounded by the lack or design of other features as well, but they don't come to mind right now. To clarify, I'm not talking about smartphones here: my plain, 2-year old phone has a CPU an order of magnitude faster than my first PC, about as much storage space and it's ridiculous how bad (slow, unwieldy) the software is and it's not one phone or one manufacturer. What keeps the (to me) obvious software functionality vacuum on a capable hardware platform from being filled up? Edit: I believe a clarification on the multitasking point might be beneficial. I'll use my phone as an example, although the point is much more general. The phone can multitask and in fact does: you can listen to music and do something else at the same time. On the other hand, the way the software has been designed makes multitasking next to useless. (Ditto with the external touch screen: it can take touch commands, but only one application makes use of it, and only with 3 commands.) To take the multitasking example to the extreme, if I plug my phone into my laptop and it registers as an external disk, it doesn't allow any kind of operation: messages, calling, calendar, everything out of reach, although I can receive a call. No "battery life" issue there: it's charging while connected. BTW, another example of design below the current state of the art: I don't see a phone on the horizon which will remember where in an audio or video file you were when you stopped listening/watching it last time (podcasts are a good use case). Simplistic rewind/fast forward functionality only aggravates the problem.

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• Opinion on "loop invariants", and are these frequently used in the industry?

  - by Michael Aaron Safyan

  I was thinking back to my freshman year at college (five years ago) when I took an exam to place-out of intro-level computer science. There was a question about loop invariants, and I was wondering if loop invariants are really necessary in this case or if the question was simply a bad example... the question was to write an iterative definition for a factorial function, and then to prove that the function was correct. The code that I provided for the factorial function was as follows: public static int factorial(int x) { if ( x < 0 ){ throw new IllegalArgumentException("Parameter must be = 0"); }else if ( x == 0 ){ return 1; }else{ int result = 1; for ( int i = 1; i <= x; i++ ){ result*=i; } return result; } } My own proof of correctness was a proof by cases, and in each I asserted that it was correct by definition (x! is undefined for negative values, 0! is 1, and x! is 1*2*3...*x for a positive value of x). The professor wanted me to prove the loop using a loop invariant; however, my argument was that it was correct "by definition", because the definition of "x!" for a positive integer x is "the product of the integers from 1... x", and the for-loop in the else clause is simply a literal translation of this definition. Is a loop invariant really needed as a proof of correctness in this case? How complicated must a loop be before a loop invariant (and proper initialization and termination conditions) become necessary for a proof of correctness? Additionally, I was wondering... how often are such formal proofs used in the industry? I have found that about half of my courses are very theoretical and proof-heavy and about half are very implementation and coding-heavy, without any formal or theoretical material. How much do these overlap in practice? If you do use proofs in the industry, when do you apply them (always, only if it's complicated, rarely, never)?

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• After HTTP GET request, the resulting string is cut-off - content has been consumed

  - by Jayomat

  hi all, I'm making a http get request like this: try { HttpClient client = new DefaultHttpClient(); String getURL = "http://busspur02.aseag.de/bs.exe?SID=5FC39&ScreenX=1440&ScreenY=900&CMD=CR&Karten=true&DatumT="+day+"&DatumM="+month+"&DatumJ="+year+"&ZeitH="+hour+"&ZeitM="+min+"&Intervall=60&Suchen=(S)uchen&GT0=Aachen&T0=H&HT0="+start_from+"&GT1=Aachen&T0=H&HT1="+destination+""; HttpGet get = new HttpGet(getURL); HttpResponse responseGet = client.execute(get); HttpEntity resEntityGet = responseGet.getEntity(); if (resEntityGet != null) { //do something with the response Log.i("GET RESPONSE",EntityUtils.toString(resEntityGet)); } ........ It all works well... the only problem: the output from Log.i is cut-off... It's not the complete html page. If I make the same request in a browser, I get 3x the output in opposition to making the request in the emulator and using the above code.... what's wrong? ERROR: 04-30 14:01:01.287: WARN/System.err(1088): java.lang.IllegalStateException: Content has been consumed 04-30 14:01:01.297: WARN/System.err(1088): at org.apache.http.entity.BasicHttpEntity.getContent(BasicHttpEntity.java:84) 04-30 14:01:01.297: WARN/System.err(1088): at org.apache.http.conn.BasicManagedEntity.getContent(BasicManagedEntity.java:100) 04-30 14:01:01.307: WARN/System.err(1088): at org.apache.http.util.EntityUtils.toString(EntityUtils.java:112) 04-30 14:01:01.307: WARN/System.err(1088): at org.apache.http.util.EntityUtils.toString(EntityUtils.java:146) 04-30 14:01:01.307: WARN/System.err(1088): at mjb.project.AVV.ParseHTML.start(ParseHTML.java:177) 04-30 14:01:01.307: WARN/System.err(1088): at mjb.project.AVV.ParseHTML.onCreate(ParseHTML.java:139) 04-30 14:01:01.307: WARN/System.err(1088): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047) 04-30 14:01:01.327: WARN/System.err(1088): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2459) 04-30 14:01:01.327: WARN/System.err(1088): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2512) 04-30 14:01:01.327: WARN/System.err(1088): at android.app.ActivityThread.access$2200(ActivityThread.java:119) 04-30 14:01:01.347: WARN/System.err(1088): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1863) 04-30 14:01:01.347: WARN/System.err(1088): at android.os.Handler.dispatchMessage(Handler.java:99) 04-30 14:01:01.347: WARN/System.err(1088): at android.os.Looper.loop(Looper.java:123) 04-30 14:01:01.347: WARN/System.err(1088): at android.app.ActivityThread.main(ActivityThread.java:4363) 04-30 14:01:01.347: WARN/System.err(1088): at java.lang.reflect.Method.invokeNative(Native Method) 04-30 14:01:01.357: WARN/System.err(1088): at java.lang.reflect.Method.invoke(Method.java:521) 04-30 14:01:01.357: WARN/System.err(1088): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:860) 04-30 14:01:01.357: WARN/System.err(1088): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:618) 04-30 14:01:01.357: WARN/System.err(1088): at dalvik.system.NativeStart.main(Native Method )

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• Advice on software / database design to avoid using cursors when updating database

  - by Remnant

  I have a database that logs when an employee has attended a course and when they are next due to attend the course (courses tend to be annual). As an example, the following employee attended course '1' on 1st Jan 2010 and, as the course is annual, is due to attend next on the 1st Jan 2011. As today is 20th May 2010 the course status reads as 'Complete' i.e. they have done the course and do not need to do it again until next year: EmployeeID CourseID AttendanceDate DueDate Status 123456 1 01/01/2010 01/01/2011 Complete In terms of the DueDate I calculate this in SQL when I update the employee's record e.g. DueDate = AttendanceDate + CourseFrequency (I pull course frequency this from a separate table). In my web based app (asp.net mvc) I pull back this data for all employees and display it in a grid like format for HR managers to review. This allows HR to work out who needs to go on courses. The issue I have is as follows. Taking the example above, suppose today is 2nd Jan 2011. In this case, employee 123456 is now overdue for the course and I would like to set the Status to Incomplete so that the HR manager can see that they need to action this i.e. get employee on the course. I could build a trigger in the database to run overnight to update the Status field for all employees based on the current date. From what I have read I would need to use cursors to loop over each row to amend the status and this is considered bad practice / inefficient or at least something to avoid if you can??? Alternatively, I could compute the Status in my C# code after I have pulled back the data from the database and before I display it on screen. The issue with this is that the Status in the database would not necessarily match what is shown on screen which just feels plain wrong to me. Does anybody have any advice on the best practice approach to such an issue? It helps, if I did use a cursor I doubt I would be looping over more than 1000 records at any given time. Maybe this is such small volume that using cursors is okay?

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• A shortest path problem with superheroes and intergalactic journeys

  - by Dman

  You are a super-hero in the year 2222 and you are faced with this great challenge: starting from your home planet Ilop you must try to reach Acinhet or else your planet will be destroyed by evil green little monsters. To do this you are given a map of the universe: there are N planets and M inter-planetary connections ( bidirectional ) that bind these planets. Each connection requires a certain time and a certain amount of fuel in order for you to cover the connection from one planet to another. The total time spent going from one planet to another is obtained by multiplying the time past to cover each connection between all the planets you go through. There are some "key planets", that allow you to refuel if you arrive on those certain "key planets". A "key planet" is the planet with the property that if it disappears the road between at least two planets would be lost.(In the example posted below with the input/output files such a "key planet" is 2 because without it the road to 7 would be lost) When you start your mission you are given the possibility of choosing between K ships each with its own maximum fuel capacity. The goal is to find the SHORTEST TIME CONSUMING path but also choose the ship with the minimum fuel capacity that can cover that shortest path(this means that if more ships can cover the shortest path you choose the one with the minimum fuel capacity). Because the minimum time can be a rather large number (over long long int) you are asked to provide only the last 6 digits of the number. For a better understanding of the task, here is an example of input/output files: INPUT: mission.in 7 8 6 1 4 6 5 9 8 7 10 1 2 7 8 1 4 14 9 1 5 3 1 2 3 1 2 2 7 7 1 3 4 2 2 4 6 4 1 5 6 3 7 On the first line (in order): N M K On the second line :the number for the starting planet and the finishing planet On the third line :K numbers that represent the capacities of the ships you can choose from Then you have M lines, all of them have the same structure: Xi Yi Ti Fi-which means that there is a connection between Xi and Yi and you can cover the distance from Xi to Yi in Ti time and with a Fi fuel consumption. OUTPUT:mission.out 000014 8 1 2 3 4 On the first line:the minimum time and fuel consumption; On the second line :the path Restrictions: 2 = N = 1 000 1 = M = 30 000 1 = K = 10 000 Any suggestions or ideas of how this problem might be solved would be most welcomed.

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• How safe is my safe rethrow?

  - by gustafc

  (Late edit: This question will hopefully be obsolete when Java 7 comes, because of the "final rethrow" feature which seems like it will be added.) Quite often, I find myself in situations looking like this: do some initialization try { do some work } catch any exception { undo initialization rethrow exception } In C# you can do it like this: InitializeStuff(); try { DoSomeWork(); } catch { UndoInitialize(); throw; } For Java, there's no good substitution, and since the proposal for improved exception handling was cut from Java 7, it looks like it'll take at best several years until we get something like it. Thus, I decided to roll my own: (Edit: Half a year later, final rethrow is back, or so it seems.) public final class Rethrow { private Rethrow() { throw new AssertionError("uninstantiable"); } /** Rethrows t if it is an unchecked exception. */ public static void unchecked(Throwable t) { if (t instanceof Error) throw (Error) t; if (t instanceof RuntimeException) throw (RuntimeException) t; } /** Rethrows t if it is an unchecked exception or an instance of E. */ public static <E extends Exception> void instanceOrUnchecked( Class<E> exceptionClass, Throwable t) throws E, Error, RuntimeException { Rethrow.unchecked(t); if (exceptionClass.isInstance(t)) throw exceptionClass.cast(t); } } Typical usage: public void doStuff() throws SomeException { initializeStuff(); try { doSomeWork(); } catch (Throwable t) { undoInitialize(); Rethrow.instanceOrUnchecked(SomeException.class, t); // We shouldn't get past the above line as only unchecked or // SomeException exceptions are thrown in the try block, but // we don't want to risk swallowing an error, so: throw new SomeException("Unexpected exception", t); } private void doSomeWork() throws SomeException { ... } } It's a bit wordy, catching Throwable is usually frowned upon, I'm not really happy at using reflection just to rethrow an exception, and I always feel a bit uneasy writing "this will not happen" comments, but in practice it works well (or seems to, at least). What I wonder is: Do I have any flaws in my rethrow helper methods? Some corner cases I've missed? (I know that the Throwable may have been caused by something so severe that my undoInitialize will fail, but that's OK.) Has someone already invented this? I looked at Commons Lang's ExceptionUtils but that does other things. Edit: finally is not the droid I'm looking for. I'm only interested to do stuff when an exception is thrown. Yes, I know catching Throwable is a big no-no, but I think it's the lesser evil here compared to having three catch clauses (for Error, RuntimeException and SomeException, respectively) with identical code. Note that I'm not trying to suppress any errors - the idea is that any exceptions thrown in the try block will continue to bubble up through the call stack as soon as I've rewinded a few things.

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• Show/Hide button (text) for Accordion

  - by Kevin

  Have an accordion with a "view" button to open close the accordion panel (using jQuery Tools), but I would like to have dynamic text that says "show/hide" depending on the state... Here is the code for the accordion in asp.NET <div id="accordion"> <% foreach (var eventModel in ViewModel) { %> <% var isNewMonth = eventModel.Date.Month != previousMonth; %> <% if (isNewMonth && previousMonth > 0) { %></table></div><% } %> <% previousMonth = eventModel.Date.Month; %> <% if (isNewMonth) { %> <h2><%= string.Concat(eventModel.Date.ToString("MMMM"), " ", eventModel.Date.Year) %> <span style="float:right;"><a href="#" class="button blue small">View</a></span></h2> <div class="pane" style="display:block"> <table id="listTable" width="100%" cellpadding="3" cellspacing="0" border="0"> <tr align="left" valign="top"><th align="left" valign="top">Date</th><th align="left" valign="top">Event</th><th align="left" valign="top">Event Type</th></tr> <% } %> <tr align="left" valign="top"><td align="left" valign="top"><b><span id="date" style="float:left;"> <%= string.Concat(eventModel.Date.ToString("MMMM"), " ", eventModel.Date.Day, " </span><span id='day' style='float:left'>" + eventModel.Date.DayOfWeek + "</span> ")%></b></td><td align="left" valign="top" ><%= Html.ActionLink(eventModel.Name.Truncate(40), "event", "register", new { id = eventModel.Id }, null)%></td><td align="left" valign="top"><%= string.Concat(" ", eventModel.Sport)%></td></tr> <% } %> <% if (ViewModel.Count > 0) { %></table></div><% } %> </div> Here is the initialization script using jQuery: $(function() { $("#accordion").tabs("#accordion div.pane", {tabs: 'h2', effect: 'slide', initialIndex: 0}); $(".small").click(function() { moveToTop(); }); });

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• Are there programs that iteratively write new programs?

  - by chris

  For about a year I have been thinking about writing a program that writes programs. This would primarily be a playful exercise that might teach me some new concepts. My inspiration came from negentropy and the ability for order to emerge from chaos and new chaos to arise out of order in infinite succession. To be more specific, the program would start by writing a short random string. If the string compiles the programs will log it for later comparison. If the string does not compile the program will try to rewrite it until it does compile. As more strings (mini 'useless' programs) are logged they can be parsed for similarities and used to generate a grammar. This grammar can then be drawn on to write more strings that have a higher probability of compilation than purely random strings. This is obviously more than a little silly, but I thought it would be fun to try and grow a program like this. And as a byproduct I get a bunch of unique programs that I can visualize and call art. I'll probably write this in Ruby due to its simple syntax and dynamic compilation and then I will visualize in processing using ruby-processing. What I would like to know is: Is there a name for this type of programming? What currently exists in this field? Who are the primary contributors? BONUS! - In what ways can I procedurally assign value to output programs beyond compiles(y/n)? I may want to extend the functionality of this program to generate a program based on parameters, but I want the program to define those parameters through running the programs that compile and assigning meaning to the programs output. This question is probably more involved than reasonable for a bonus, but if you can think of a simple way to get something like this done in less than 23 lines or one hyperlink, please toss it into your response. I know that this is not quite meta-programming and from the little I know of AI and generative algorithms they are usually more goal oriented than what I am thinking. What would be optimal is a program that continually rewrites and improves itself so I don't have to ^_^

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• ASP.NET- forcing child/container events to fire before parent onload?

  - by Hans Gruber

  I'm working on a questionnaire type application in which questions are stored in a database. Therefore, I create my controls dynamically on every Page.OnLoad. This works like a charm and ViewState is persisted between postbacks because I ensure that my dynamic controls always have the same generated Control.ID. In addition to the user control that dynamically populates the questions, my questionnaire page also contains a 'Status' section (also encapsulated by a user control) which represents the status of the questionnaire (choices are 'Complete', 'Started' or 'In Progress'). If the user changes the status of questionnaire (i.e. from 'In Progress' to 'Complete'), I need to postback to the server because the contents of the dynamic portion of the questionnaire depend on the selected status. Some questions are always present regardless of status, and yet others may not be present at all for the selected status. The point is, when the status changes, I have to postback to the page and render the right set of questions. Additionally, I need to preserve any user entered values for those questions which are 'always available'. However, due to the page life cycle in ASP.NET, the 'Status' user control's OnLoad, which contains the correct status needed to load the right questions from the DB, doesn't get executed until after the 'dynamic questions' user control has already been populated (with the wrong/stale values). To get around this, I raise an event from my 'Status' user control to the main page to indicate that the Status has changed. The main page then raises an event on the 'dynamic questions' user control. Since by the time this event bubbles up, the 'dynamic questions' user control has already loaded the 'wrong' questions from the DB, it first calls Controls.Clear. It then happily uses the new status to query the database for the 'correct' questions and does a Control.Add() on each. FYI, Control.IDs are consistent across postbacks. This solution works...sorta. The correct set of questions for the selected status do get rendered; however ViewState is getting lost for those 'always available' questions. I'm guessing this is because the 'dynamic questions' user control calls Controls.Clear when responding to the status changed event. This must somehow kill the association between ViewState and my dynamic controls, even though the Control.ID are consistent. This seems like such a common requirement, I'm virtually certain there is a better, cleaner and less error prone approach to accomplish this. In case its not plain obvious, I haven't been able to grok the ASP.NET page life-cycle despite working with it for the last year. Any help is much appreciated!

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• Keeping track of business rules within IT department?

  - by evaldas-alexander

  I am looking for the best way to keep track of the business rules for both developers and everybody else (support staff / management) in a startup enviroment. The challenge is that our business model requires quite a lot of different business rules, which are created pretty much on the fly and evolving organically after that. After running this project for 3+ years, we have so many of such rules that often the only way to be sure about what the application is supposed to do in a certain situation is to go find the module responsible for that process and analyze its code and comments. That is all fine as long as you have one single developer who created the entire application from the scratch, but every new developer needs to go over pretty much entire codebase in order to understand how the application works. Even bigger problem is that non technical employees don't even have that option and therefore are forced to ask me pretty much every day how some certain case would be handled by the application. Quick example - we only start charging for our customer campaigns once they have been active for at least 72 hours, but at the same time we stop creating invoices for campaigns that belong to insolvent accounts and close such accounts within a month of the first failed charge. That does not apply to accounts that are set to "non-chargeable" which most commonly belongs to us since we are using the service ourselves. The invoices are created on the 1st of each month and include charges from the previous month + any current balance that the account might have. However, some customers are charged only 4 days after their invoice has been generated due to issues with their billing department. In addition to that, invoices are also created when customer deactivates his campaign, but that can only be done once the campaign is not longer under mandatory 6 month contract, unless account manager approves early deactivation. I know, that's quite a lot of rules that need to be taken into account when answering a question "when do we bill our customers", but actually I could still append an asterisk at the end of each sentence in order to disclose some rare exceptions. Of course, it would be easiest just to keep the business rules to the minimum, but we need to adapt to changing marketplace - i.e. less than a year ago we had no contracts whatsoever. One idea that I had so far was a simplistic wiki with categories corresponding to areas such as "Account activation", "Invoicing", "Collection procedures" and so on. Another idea would be to have giant interactive flowchart showing the entire customer "life cycle" from prospecting to account deactivation. What are your experiences / suggestions?

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• My style/control template out my calendar's blackout dates.

  - by Chris

  Howdy, My C#/WPF project needs a calendar. We're going to be using it to pick a range of dates for appointment scheduling. I'm told the default calendar is too small to be used by some of our reps so I've been working on resizing it. <toolkit:Calendar Grid.Row="1" x:Name="DateWindowCalendar" BorderBrush="White" BorderThickness="0" Style="{StaticResource PopupCalendarStyle}" DisplayMode="Month" SelectionMode="SingleRange" DisplayDateStart="{Binding FirstDayOfMonth}" AutomationProperties.AutomationId="ToolkitCalendarId" VerticalAlignment="Top"> </toolkit:Calendar> And I've created this styling: <Style x:Key="PopupCalendarStyle" TargetType="toolkit:Calendar"> <Setter Property="Template"> <Setter.Value> <ControlTemplate TargetType="toolkit:Calendar"> <StackPanel Margin="0" HorizontalAlignment="Center" x:Name="Root"> <toolkit:Calendar x:Name="Calendar" SelectedDate="{TemplateBinding SelectedDate}" DisplayDateStart="{TemplateBinding DisplayDateStart}" SelectionMode="{TemplateBinding SelectionMode}" Background="{TemplateBinding Background}" BorderBrush="{TemplateBinding BorderBrush}" BorderThickness="{TemplateBinding BorderThickness}" SelectedDatesChanged="Calendar_SelectedDatesChanged"> <toolkit:Calendar.CalendarDayButtonStyle> <Style> <Setter Property="Button.Height" Value="34"/> <Setter Property="Button.Width" Value="34" /> <Setter Property="Button.FontSize" Value="16" /> </Style> </toolkit:Calendar.CalendarDayButtonStyle> <toolkit:Calendar.CalendarButtonStyle> <Style> <Setter Property="Button.Height" Value="34"/> <Setter Property="Button.Width" Value="34"/> <Setter Property="Button.FontSize" Value="16"/> </Style> </toolkit:Calendar.CalendarButtonStyle> </toolkit:Calendar> </StackPanel> </ControlTemplate> </Setter.Value> </Setter> </Style> Everything is almost perfect. I specify my range, I can track the selected dates (granted using the SelectedDatesChanged event instead of the SelectedDates property. The problem is I also need to be able to set blackout dates (usually the period between first of the month and today although sometimes first of the month to a few days from now). Without the styling, this works: DateWindowCalendar.BlackoutDates.Add(new CalendarDateRange( new DateTime(DateTime.Now.Year, DateTime.Now.Month, 01), DateTime.Now)); But when I add the style, I don't get the black out displays being displayed and worse its possible to select the blackout dates. I'm not sure what I missed but I'm hoping someone has an easy answer so that I don't have to rebuild the entire widget. Any help is appreciated. Thanks, Chris

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• MacRuby + Interface Builder: How to display, then close, then display a window again

  - by Derick Bailey

  I'm a complete n00b with MacRuby and Cocoa, though I've got more than a year of Ruby experience, so keep that in mind when answering - I need lots of details and explanation. :) I've set up a simple project that has 2 windows in it, both of which are built with Interface Builder. The first window is a simple list of accounts using a table view. It has a "+" button below the table. When I click the + button, I want to show an "Add New Account" window. I also have an AccountsController < NSWindowController and a AddNewAccountController class, set up as the delegates for these windows, with the appropriate button click methods wired up, and outlets to reference the needed windows. When I click the "+" button in the Accounts window, I have this code fire: @add_account.center @add_account.display @add_account.makeKeyAndOrderFront(nil) @add_account.orderFrontRegardless this works great the first time I click the + button. Everything shows up, I'm able to enter my data and have it bind to my model. however, when I close the add new account form, things start going bad. if I set the add new account window to release on close, then the second time I click the + button, the window will still pop up but it's frozen. i can't click any buttons, enter any data, or even close the form. i assume this is because the form's code has been released, so there is no message loop processing the form... but i'm not entirely sure about this. if i set the add new account window to not release on close, then the second time i click the + button, the window shows up fine and it is usable - but it still has all the data that i had previously entered... it's still bound to my previous Account class instance. what am I doing wrong? what's the correct way to create a new instance of the Add New Account form, create a new Account model, bind that model to the form and show the form, when I click the + button on the Accounts form? ... this is all being done on OSX 10.6.6, 64bit, with XCode 3.2.4

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• Difficulty adding widgets to django form.

  - by codingJoe

  I have a django app that tracks activities that can benefit a classroom. Using the django examples, I was able to build a form to enter this data. But when I try to add widgets to that form, things get tricky. What I want is a calendar widget that lets the user enter the 'activity_date' field using a widget. If I use Admin interface. The AdminDateWidget works fine. however. This particular user isn't allowed access to the admin interface so I need a different way to present this widget. Also I couldn't figure out how to make the bring the admin widget over into non-admin pages. So I tried a custom widget. This is the first custom widget I've built, so I'm not quite sure what is supposed to be going on here. Any Expert Advice? How do I get my date widget to work? # The Model class Activity(models.Model): activity_date = models.DateField() activity_type = models.CharField(max_length=50, choices=ACTIVITY_TYPES) activity_description = models.CharField(max_length=200) activity_duration= models.DecimalField(decimal_places=2, max_digits=4) est_attendance = models.IntegerField("Estimated attendance") # The Form class ActivityForm(forms.ModelForm): # The following line causes lockup if enabled. # With the DateTimeWidget removed, the form functions correctly except that there is no widget. #activity_date = forms.DateField(label=_('Date'), widget=DateTimeWidget) ##!!! Point of Error !!! class Meta: model = Activity fields = ('activity_date', 'activity_type', 'activity_description', 'activity_duration', 'est_attendance') def __init__(self, *args, **kwargs): super(ActivityForm, self).__init__(*args, **kwargs) instance = getattr(self, 'instance', None) edit_aid = kwargs.get('edit_aid', False) # On a different approach, the following also didn't work. #self.fields['activity_date'].widget = widgets.AdminDateWidget() # The Widget # Example referenced: http://djangosnippets.org/snippets/391/ calbtn = u""" <button id="calendar-trigger">...</button> <img src="%s/site_media/images/icon_calendar.gif" alt="calendar" id="%s_btn" style="cursor: pointer; border: 1px solid #8888aa;" title="Select date and time" onmouseover="this.style.background='#444444';" onmouseout="this.style.background=''" /> <script type="text/javascript"> Calendar.setup({ trigger : "calendar-trigger", inputField : "%s" }); </script>""" class DateTimeWidget(forms.widgets.TextInput): dformat = '%Y-%m-%d %H:%M' def render(self, name, value, attrs=None): print "DTWgt render name=%s, value=%s" % name, value if value is None: value = '' final_attrs = self.build_attrs(attrs, type=self.input_type, name=name) if value != '': try: final_attrs['value'] = \ force_unicode(value.strftime(self.dformat)) except: final_attrs['value'] = \ force_unicode(value) if not final_attrs.has_key('id'): final_attrs['id'] = u'%s_id' % (name) id = final_attrs['id'] jsdformat = self.dformat #.replace('%', '%%') cal = calbtn % (settings.MEDIA_URL, id, id, jsdformat, id) a = u'<input%s />%s' % (forms.util.flatatt(final_attrs), cal) print "render return %s " % a return mark_safe(a) def value_from_datadict(self, data, files, name): print "DTWgt value_from_datadict" dtf = forms.fields.DEFAULT_DATETIME_INPUT_FORMATS empty_values = forms.fields.EMPTY_VALUES value = data.get(name, None) if value in empty_values: return None if isinstance(value, datetime.datetime): return value if isinstance(value, datetime.date): return datetime.datetime(value.year, value.month, value.day) for format in dtf: try: return datetime.datetime(*time.strptime(value, format)[:6]) except ValueError: continue return None

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• How to solve Python memory leak when using urrlib2?

  - by b_m

  Hi, I'm trying to write a simple Python script for my mobile phone to periodically load a web page using urrlib2. In fact I don't really care about the server response, I'd only like to pass some values in the URL to the PHP. The problem is that Python for S60 uses the old 2.5.4 Python core, which seems to have a memory leak in the urrlib2 module. As I read there's seems to be such problems in every type of network communications as well. This bug have been reported here a couple of years ago, while some workarounds were posted as well. I've tried everything I could find on that page, and with the help of Google, but my phone still runs out of memory after ~70 page loads. Strangely the Garbege Collector does not seem to make any difference either, except making my script much slower. It is said that, that the newer (3.1) core solves this issue, but unfortunately I can't wait a year (or more) for the S60 port to come. here's how my script looks after adding every little trick I've found: import urrlib2, httplib, gc while(true): url = "http://something.com/foo.php?parameter=" + value f = urllib2.urlopen(url) f.read(1) f.fp._sock.recv=None # hacky avoidance f.close() del f gc.collect() Any suggestions, how to make it work forever without getting the "cannot allocate memory" error? Thanks for advance, cheers, b_m update: I've managed to connect 92 times before it ran out of memory, but It's still not good enough. update2: Tried the socket method as suggested earlier, this is the second best (wrong) solution so far: class UpdateSocketThread(threading.Thread): def run(self): global data while 1: url = "/foo.php?parameter=%d"%data s = socket.socket(socket.AF_INET, socket.SOCK_STREAM) s.connect(('something.com', 80)) s.send('GET '+url+' HTTP/1.0\r\n\r\n') s.close() sleep(1) I tried the little tricks, from above too. The thread closes after ~50 uploads (the phone has 50MB of memory left, obviously the Python shell has not.) UPDATE: I think I'm getting closer to the solution! I tried sending multiple data without closing and reopening the socket. This may be the key since this method will only leave one open file descriptor. The problem is: import socket s=socket.socket(socket.AF_INET, socket.SOCK_STREAM) socket.connect(("something.com", 80)) socket.send("test") #returns 4 (sent bytes, which is cool) socket.send("test") #4 socket.send("test") #4 socket.send("GET /foo.php?parameter=bar HTTP/1.0\r\n\r\n") #returns the number of sent bytes, ok socket.send("GET /foo.php?parameter=bar HTTP/1.0\r\n\r\n") #returns 0 on the phone, error on Windows7* socket.send("GET /foo.php?parameter=bar HTTP/1.0\r\n\r\n") #returns 0 on the phone, error on Windows7* socket.send("test") #returns 0, strange... *: error message: 10053, software caused connection abort Why can't I send multiple messages??

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• Creating a music catalog and extracting first 30 seconds as soon as the first words are sung

  - by Rad

  I already read a question: Separation of singing voice from music. I don’t need this complex audio processing. I only need some detection mechanism that would detect that there is some voice/vocal playing while the music is playing (or not playing) I need to extract first 30 seconds when a vocalist starts singing along with full band music. See question 2 below. I want to create a music catalog using ASP.NET MVC 2 and Silverlight clients and C#.NET 4.0 programming language that would be front store. On the backend I would also like to create a desktop WPF/Windows application to create the music catalog from already existing music files, most of which have metadata in them ID3v1, ID3v2.3, ID3v2.4, iTunes MP4, WMA, Vorbis Comments and APE Tags etc. I would possibly like to create a web service that would allow catalog contributors to upload a zipped album and trigger metadata extraction of music data and extraction of music segments as described below. I would be happy if I achieve no. 1 below. Let's say I have 1000ths of songs in mp3 (or other formats) grouped in subfolders using some classification (Genre, Artists, Albums, Composers or other groupings). I want to create tables in DB that would organize songs so they can be searched based on different criteria (year, length, above classification or by song title, description etc) like what iTune store allows to their customers. I want to extract metadata from various formats (I will try to get songs in mp3 format, but there may be other popular formats) and allow music Catalog manager person to add missing data from either desktop or web applications. He or other contributors can upload zipped music via an HTML or Silverlight upload or WPF. Can anybody suggest open source libraries, articles, code snippets that can do that in an automatic way using .NET and possibly SQL Server DB? My main questions are these. This is an audio processing challenge. I want to extract 2 segments of music (questions 1 and 2): 1. How to extract a music segment: 1-2 seconds before a vocal starts singing and up to 30 seconds from that point in time and 2. Much more challenging is to find repeating segments (One would usually find or recognize the names of the songs and songs are usually known by these refrains. How would I go about creating a list of songs that go great together like what Genius from iTune does? Is there any characteristics of music that can be used to match songs? The goal is for people quickly scan and recognize songs i.e. associate melody, words with a title/album so they can make intelligent decisions like buying a song, create similar mood songs.

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• how to solve the errors of this program

  - by hussein abdullah

  include using std::cout; using std::cin; using std::endl; include void initialize(char[],int*); void input(const char[] ,int&); void print ( const char*,const int); void growOlder (const char [], int* ); bool comparePeople(const char* ,const int*,const char*,const int*); int main(){ char name1[25]; char name2[25]; int age1; int age2; initialize (name1,&age1); initialize (name2,&age2); print(name1,*age1); print(name2,*age2); input(name1,age1); input(name2,age2); print(&name1,&age1); print(&name2,&age2); growOlder(name2,age2); if(comparePeople(name1,&age1,name2,&age2)) cout<<"Both People have the same name and age "<<endl; return 0; } void input(const char name[],int &age) { cout<<"Enter a name :"; cinname ; cout<<"Enter an age:"; cin>>age; cout<<endl; } void initialize ( char name[],int *age) { name=""; age=0; } void print ( const char name[],const int age ) { cout<<"The Value stored in variable name is :" < void growOlder(const char name[],int *age) { cout<< name <<" has grown one year older\n\n"; *age++; } bool comparePeople (const char *name1,const int *age1, const char *name2,const int *age2) { return(age1==age2 &&strcmp(name1,name2)); }

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• Windows 7 - pydoc from cmd

  - by Random_Person

  Okay, I'm having one of those moments that makes me question my ability to use a computer. This is not the sort of question I imagined asking as my first SO post, but here goes. Started on Zed's new "Learn Python the Hard Way" since I've been looking to get back into programming after a 10 year hiatus and python was always what I wanted. This book has really spoken to me. That being said, I'm having a serious issue with pydoc from the command. I've got all the directories in c:/python26 in my system path and I can execute pydoc from the command line just fine regardless of pwd - but it accepts no arguments. Doesn't matter what I type, I just get the standard pydoc output telling me the acceptable arguments. Any ideas? For what it's worth, I installed ActivePython as per Zed's suggestion. C:\Users\Chevee>pydoc file pydoc - the Python documentation tool pydoc.py <name> ... Show text documentation on something. <name> may be the name of a Python keyword, topic, function, module, or package, or a dotted reference to a class or function within a module or module in a package. If <name> contains a '\', it is used as the path to a Python source file to document. If name is 'keywords', 'topics', or 'modules', a listing of these things is displayed. pydoc.py -k <keyword> Search for a keyword in the synopsis lines of all available modules. pydoc.py -p <port> Start an HTTP server on the given port on the local machine. pydoc.py -g Pop up a graphical interface for finding and serving documentation. pydoc.py -w <name> ... Write out the HTML documentation for a module to a file in the current directory. If <name> contains a '\', it is treated as a filename; if it names a directory, documentation is written for all the contents. C:\Users\Chevee> EDIT: New information, pydoc works just fine in PowerShell. As a linux user, I have no idea why I'm trying to use cmd anyways--but I'd still love to figure out what's up with pydoc and cmd. EDIT 2: More new information. In cmd... c:\>python c:/python26/lib/pydoc.py file ...works just fine. Everything works just fine with just pydoc in PowerShell without me worrying about pwd, or extensions or paths.

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