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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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• XCode sqlite3 - SELECT always return SQLITE_DONE

  - by user573633

  Hi developers.... a noob here asking for help after a day of head-banging.... I am working on an app with sqlite3 database with one database and two tables. I have now come to a step where I want to select from the table with an argument. The code is here: -(NSMutableArray*) getGroupsPeopleWhoseGroupName:(NSString*)gn;{ NSMutableArray *groupedPeopleArray = [[NSMutableArray alloc] init]; const char *sql = "SELECT * FROM Contacts WHERE groupName='?'"; @try { NSArray * paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory,NSUserDomainMask, YES); NSString *docsDir = [paths objectAtIndex:0]; NSString *theDBPath = [docsDir stringByAppendingPathComponent:@"ContactBook.sqlite"]; if (!(sqlite3_open([theDBPath UTF8String], &database) == SQLITE_OK)) { NSLog(@"An error opening database."); } sqlite3_stmt *st; NSLog(@"debug004 - sqlite3_stmt success."); if (sqlite3_prepare_v2(database, sql, -1, &st, NULL) != SQLITE_OK) { NSLog(@"Error, failed to prepare statement."); } //DB is ready for accessing, now start getting all the info. while (sqlite3_step(st) == SQLITE_ROW) { MyContacts * aContact = [[MyContacts alloc] init]; //get contactID from DB. aContact.contactID = sqlite3_column_int(st, 0); if (sqlite3_column_text(st, 1) != NULL) { aContact.firstName = [NSString stringWithUTF8String:(char *) sqlite3_column_text(st, 1)]; } else { aContact.firstName = @""; } // here retrieve other columns data .... //store these info retrieved into the newly created array. [groupedPeopleArray addObject:aContact]; [aContact release]; } if(sqlite3_finalize(st) != SQLITE_OK) { NSLog(@"Failed to finalize data statement."); } if (sqlite3_close(database) != SQLITE_OK) { NSLog(@"Failed to close database."); } } @catch (NSException *e) { NSLog(@"An exception occurred: %@", [e reason]); return nil; } return groupedPeopleArray;} MyContacts is the class where I put up all the record variables. My problem is sqlite3_step(st) always return SQLITE_DONE, so that it i can never get myContacts. (i verified this by checking the return value). What am I doing wrong here? Many thanks in advance!

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• CQRS - Should a Command try to create a "complex" master-detail entity?

  - by Simon Crabtree

  I've been reading Greg Young and Udi Dahan's thoughts on Command Query Responsibilty Separation and a lot of what I read strikes a chord with me. My domain (we track vehicles which are doing deliveries) has the concept of a Route which contains one or more Stops. I need my customers to be able to set these up in our system by calling a webservice, and then be able to retrieve information about a Route and how the vehicle is progressing. In the past I would have "cut-down" DTO classes which closely resemble my domain classes, and the customer would create a RouteDto with an array of StopDto(s), and call our CreateRoute webmethod, passing in the RouteDto. When they query our system by calling the GetRouteDetails method, I would return exactly the same objects to them. One of the appealing aspects of CQRS is that the RouteDto might have all manner of properties that the customer wants to query, but have no business setting when they create a Route. So I create a separate CreateRouteRequest class which is passed in when calling the CreateRoute "command", and a Route DTO class which gets returned as a query result. class Route{ string Reference; List<Stop> Stops; } But I need my customer to provide me with Route AND Stop details when they create a route. As I see it I could either... Give my CreateRouteRequest class a Stops(s) property which is an array of "something" representing the data they need to provide about each stop - but what do I call this class? It's not a Stop as that's what I'm calling the list of DTO inside my Route DTO, but I don't like "CreateStopRequest". I also wonder if I'm stuck in a CRUD mindset here thinking in terms of master-detail information and asking the customer to think like that too. class CreateRouteRequest{ string Reference; ... List<CreateStopRequest> Stops; } or They call CreateRoute, and then make a number of calls to an AddStopToRoute method. This feels a bit more "behavioural" but I'm going to lose the ability to treat creating a route including its stops as a single atomic command. If they create a Route and then try to add a Stop which fails due to some validation problem they're going to have a partially correct Route. The fact that I can't come up with a good name for the list of "StopCreationData" objects I'd be working with in option 1, makes me wonder if there's something I'm missing.

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• Clojure vars and Java static methods

  - by j-g-faustus

  I'm a few days into learning Clojure and are having some teething problems, so I'm asking for advice. I'm trying to store a Java class in a Clojure var and call its static methods, but it doesn't work. Example: user=> (. java.lang.reflect.Modifier isPrivate 1) false user=> (def jmod java.lang.reflect.Modifier) #'user/jmod user=> (. jmod isPrivate 1) java.lang.IllegalArgumentException: No matching method found: isPrivate for class java.lang.Class (NO_SOURCE_FILE:0) at clojure.lang.Compiler.eval(Compiler.java:4543) From the exception it looks like the runtime expects a var to hold an object, so it calls .getClass() to get the class and looks up the method using reflection. In this case the var already holds a class, so .getClass() returns java.lang.Class and the method lookup obviously fails. Is there some way around this, other than writing my own macro? In the general case I'd like to have either an object or a class in a varible and call the appropriate methods on it - duck typing for static methods as well as for instance methods. In this specific case I'd just like a shorter name for java.lang.reflect.Modifier, an alias if you wish. I know about import, but looking for something more general, like the Clojure namespace alias but for Java classes. Are there other mechanisms for doing this? Edit: Maybe I'm just confused about the calling conventions here. I thought the Lisp (and by extension Clojure) model was to evaluate all arguments and call the first element in the list as a function. In this case (= jmod java.lang.reflect.Modifier) returns true, and (.getName jmod) and (.getName java.lang.reflect.Modifier) both return the same string. So the variable and the class name clearly evaluate to the same thing, but they still cannot be called in the same fashion. What's going on here? Edit 2 Answering my second question (what is happening here), the Clojure doc says that If the first operand is a symbol that resolves to a class name, the access is considered to be to a static member of the named class... Otherwise it is presumed to be an instance member http://clojure.org/java_interop under "The Dot special form" "Resolving to a class name" is apparently not the same as "evaluating to something that resolves to a class name", so what I am trying to do here is something the dot special form does not support.

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• Code golf - hex to (raw) binary conversion

  - by Alnitak

  In response to this question asking about hex to (raw) binary conversion, a comment suggested that it could be solved in "5-10 lines of C, or any other language." I'm sure that for (some) scripting languages that could be achieved, and would like to see how. Can we prove that comment true, for C, too? NB: this doesn't mean hex to ASCII binary - specifically the output should be a raw octet stream corresponding to the input ASCII hex. Also, the input parser should skip/ignore white space. edit (by Brian Campbell) May I propose the following rules, for consistency? Feel free to edit or delete these if you don't think these are helpful, but I think that since there has been some discussion of how certain cases should work, some clarification would be helpful. The program must read from stdin and write to stdout (we could also allow reading from and writing to files passed in on the command line, but I can't imagine that would be shorter in any language than stdin and stdout) The program must use only packages included with your base, standard language distribution. In the case of C/C++, this means their respective standard libraries, and not POSIX. The program must compile or run without any special options passed to the compiler or interpreter (so, 'gcc myprog.c' or 'python myprog.py' or 'ruby myprog.rb' are OK, while 'ruby -rscanf myprog.rb' is not allowed; requiring/importing modules counts against your character count). The program should read integer bytes represented by pairs of adjacent hexadecimal digits (upper, lower, or mixed case), optionally separated by whitespace, and write the corresponding bytes to output. Each pair of hexadecimal digits is written with most significant nibble first. The behavior of the program on invalid input (characters besides [a-fA-F \t\r\n], spaces separating the two characters in an individual byte, an odd number of hex digits in the input) is undefined; any behavior (other than actively damaging the user's computer or something) on bad input is acceptable (throwing an error, stopping output, ignoring bad characters, treating a single character as the value of one byte, are all OK) The program may write no additional bytes to output. Code is scored by fewest total bytes in the source file. (Or, if we wanted to be more true to the original challenge, the score would be based on lowest number of lines of code; I would impose an 80 character limit per line in that case, since otherwise you'd get a bunch of ties for 1 line).

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• Parsing secure entries XML file with jquery

  - by user573131

  Apologies if this is elementary. I'm primarily a front end designer/dev. I have webform through a form service called wufoo. Wufoo generates a lovely XML (or json) file that can be grabed and parsed. I'm trying to grab the entries xml feed that is associated with the form and parse it via jquery to show who has entered. Im using the following code (which works with a local xml file). http://bostonwebsitemakeover.com/2/test <script type="text/javascript" src="http://ajax.googleapis.com/ajax/libs/jquery/1.3.2/jquery.js"></script> <script> $(document).ready(function () { $.ajax({ type: "GET", url: "people.xml", dataType: "xml", success: xmlParser }); }); function xmlParser(xml) { $('#load').fadeOut(); $(xml).find("Entry").each(function () { $(".main").append('<div class="entry">' + $(this).find("Field1").text() + ' ' + $(this).find("Field2").text() + ' http://twitter.com/' + $(this).find("Field17").text() + '</div>'); $(".entry").fadeIn(1000); }); } </script> My XML file contains the following: <?xml version="1.0"?> <Entries> <Entry> <EntryId>1</EntryId> <Field1>Meaghan</Field1> <Field2>Severson</Field2> <Field17/> </Entry> <Entry> <EntryId>2</EntryId> <Field1>Michael</Field1> <Field2>Flint</Field2> <Field17>michaelflint</Field17> </Entry> <Entry> <EntryId>3</EntryId> <Field1>Niki</Field1> <Field2>Brown</Field2> <Field17>nikibrown</Field17> </Entry> <Entry> <EntryId>4</EntryId> <Field1>Niki</Field1> <Field2>Brown</Field2> <Field17>nikibrown</Field17> </Entry> </Entries> I'm wondering how I would do this with the xml file hosted on the wufoo (which is https) So I guess Im asking how do I authenticate the feed via jquery? Or do i need to do this via json? Could someone explain how?

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• Looking for an Open Source Project in need of help

  - by hvidgaard

  Hi StackOverflow! I'm a CS student on well on my way to graduate. I have had a difficult time of finding relevant student jobs (they seems to be taken merely hours after the notice gets on the board) , so instead I'm looking for an open source project in need of help. I'm aware that I should choose one that I use, but I'm not aware of any OS-project that I use that needs help. That's why I'm asking you. I don't have any deep experience, but I here are some of my biggest projects so far: BitTorrent-ish client in Python (a subset of BitTorrent) HTTP 1.1 webserver in Java Compiler from a subset of Java to run on JRE Flash-framework project to model an iPad look and feel (not to run actual iPad programs) complete with an API for programs. Complete MySQL database for a booking system, with departure and arrival times, so you could only book valid tickets (with a Java frontend). I know, Java and languages like AS3 and C# feels natural per se, Python, and have done a fair bit of hacking around in C, but I don't feel very comfortable with it. Mostly I'm afraid to make a fuckup because I have such a high degree of control. I would like to think I'm well aware of good software design practices, but in reality what I do is ask myself "would I like to use/maintain this?", and I love to refactor my code because I see optimizations. I love algorithms and to make them run in the best possible time. I don't have any preferred domain to work in, but I wouldn't mind it to be graphics or math heavy. Ideally I'm looking for a project in C++ to learn the in's and out's of it, but I'm well aware that I don't know that language very well. I would like to have a mentor-like figure until I'm confident enough to stand on my own, not one to review all my code (I'm sure someone will to start with anyway), but to ask questions about the project and language in question. I do have a wife and two children, so don't expect me to put in 10+ hours every week. In return I can work on my own, I strive to program modular and maintainable code. Know how to read an API, use Google, StackOverflow and online resources in general. If you have any questions, shoot. I'm looking forward to your suggestions.

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• Question about Architecture for Viewing Images in ASP.NET MVC App

  - by Charlie Flowers

  I have an approach in mind for an image viewer in a web app, and want to get a sanity check and any thoughts you stackoverflowers might have. Here's the whirlwind nutshell summary: I'm working on an ASP.NET MVC application that will run in my company's retail stores. Even though it is a web application, we own the store machines and have control over them. We have a "windows agent" running on the store machine which we can talk to from the browser via javascript (it is a WCF service, and our web app has permission to talk to it from the browser). One of the web pages needs to be an "image viewer" page with some common things like Rotate & Zoom. Now, there are some WebForms controls that offer Rotate and Zoom. However, they take up server resources and generate a good bit of traffic between the server and the browser. For example, the Rotate function would cause an ajax call to the server, which would then generate a new image written to a .NET Canvas object, which would then be written to a file on the server, which would then be returned from the ajax call and refreshed inside the browser. Normally, that's a pretty good way of doing things. But in our case, we have code running on the store machine that we can communicate with. This leads me to consider the following approach: When the user asks to view an image, we tell our "windows agent" to download it from our image server to the store machine. We then redirect our browser to our image viewer page, which will pull the image from the local file we just wrote to the store machine. When the user clicks "Rotate", we cause JavaScript code in the browser to call our "windows agent" software, asking it to perform the "Rotate" function. The "windows agent" does the rotation using the same kind of imaging control that would formerly have been used on the server, but it does so now on the store machine. Javascript in the browser then refreshes the image on the page to show the newly rotated image. Zoom and similar features would be implemented the same way. This seems to be much more efficient, scalable, and responsive for the end-users. However, I've never heard of anything like it being done, mostly because it's rare to have this combination of a web app plus a "windows agent" on the client machine. What do you think? Feasible? Reasonable? Any pitfalls I overlooked or improvements / suggestions you can see? Has anyone done anything like this who would like to offer the wisdom of experience? Thanks!

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• Java app makes screen display unresponsive after 10 minutes of user idle time

  - by Ross

  I've written a Java app that allows users to script mouse/keyboard input (JMacro, link not important, only for the curious). I personally use the application to automate character actions in an online game overnight while I sleep. Unfortunately, I keep coming back to the computer in the morning to find it unresponsive. Upon further testing, I'm finding that my application causes the computer to become unresponsive after about 10 minutes of user idle time (even if the application itself it simulating user activity). I can't seem to pin-point the issue, so I'm hoping somebody else might have a suggestion of where to look or what might be causing the issue. The relevant symptoms and characteristics: Unresponsiveness occurs after user is idle for 10 minutes User can still move the mouse pointer around the screen Everything but the mouse appears frozen... mouse clicks have no effect and no applications update their displays, including the Windows 7 desktop I left the task manager up along the with the app overnight so I could see the last task manager image before the screen freezes... the Java app is at normal CPU/Memory usage and total CPU usage is only ~1% After moving the mouse (in other words, the user comes back from being idle), the screen image starts updating again within 30 minutes (this is very hit and miss... sometimes 10 minutes, sometimes no results after two hours) User can CTRL-ALT-DEL to get to Windows 7's CTRL-ALT-DEL screen (after a 30 second pause). User is still able to move mouse pointer, but clicking any of the button options causes the screen to appear to freeze again On some very rare occasions, the system never freezes, and I come back to it in the morning with full responsiveness The Java app automatically stops input scripting in the middle of the night, so Windows 7 detects "real" idleness and turns the monitors into Standby mode... which they successfully come out of upon manually moving the mouse in the morning when I wake up, even though the desktop display still appears frozen Given the symptoms and characteristics of the issue, it's as if the Java app is causing the desktop display of the logged in user to stop updating, including any running applications. Programming concepts and Java packages used: Multi-threading Standard out and err are rerouted to a javax.swing.JTextArea The application uses a Swing GUI awt.Robot (very heavily used) awt.PointerInfo awt.MouseInfo System Specs: Windows 7 Professional Java 1.6.0 u17 In conclusion, I should stress that I'm not looking for any specific solutions, as I'm not asking a very specific question. I'm just wondering if anybody has run into a similar problem when using the Java libraries that I'm using. I would also gladly appreciate any suggestions for things to try to attempt to further pinpoint what is causing my problem. Thanks! Ross PS, I'll post an update/answer if I manage to stumble across anything else while I continue to debug this.

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• Some clarification on rvalue references

  - by Dennis Zickefoose

  First: where are std::move and std::forward defined? I know what they do, but I can't find proof that any standard header is required to include them. In gcc44 sometimes std::move is available, and sometimes its not, so a definitive include directive would be useful. When implementing move semantics, the source is presumably left in an undefined state. Should this state necessarily be a valid state for the object? Obviously, you need to be able to call the object's destructor, and be able to assign to it by whatever means the class exposes. But should other operations be valid? I suppose what I'm asking is, if your class guarantees certain invariants, should you strive to enforce those invariants when the user has said they don't care about them anymore? Next: when you don't care about move semantics, are there any limitations that would cause a non-const reference to be preferred over an rvalue reference when dealing with function parameters? void function(T&); over void function(T&&); From a caller's perspective, being able to pass functions temporary values is occasionally useful, so it seems as though one should grant that option whenever it is feasible to do so. And rvalue references are themselves lvalues, so you can't inadvertently call a move-constructor instead of a copy-constructor, or something like that. I don't see a downside, but I'm sure there is one. Which brings me to my final question. You still can not bind temporaries to non-const references. But you can bind them to non-const rvalue references. And you can then pass along that reference as a non-const reference in another function. void function1(int& r) { r++; } void function2(int&& r) { function1(r); } int main() { function1(5); //bad function2(5); //good } Besides the fact that it doesn't do anything, is there anything wrong with that code? My gut says of course not, since changing rvalue references is kind of the whole point to their existence. And if the passed value is legitimately const, the compiler will catch it and yell at you. But by all appearances, this is a runaround of a mechanism that was presumably put in place for a reason, so I'd just like confirmation that I'm not doing anything foolish.

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• Memory Leak with Swing Drag and Drop

  - by tom

  I have a JFrame that accepts top-level drops of files. However after a drop has occurred, references to the frame are held indefinitely inside some Swing internal classes. I believe that disposing of the frame should release all of its resources, so what am I doing wrong? Example import java.awt.datatransfer.DataFlavor; import java.io.File; import java.util.List; import javax.swing.JFrame; import javax.swing.JLabel; import javax.swing.TransferHandler; public class DnDLeakTester extends JFrame { public static void main(String[] args) { new DnDLeakTester(); //Prevent main from returning or the jvm will exit while (true) { try { Thread.sleep(10000); } catch (InterruptedException e) { } } } public DnDLeakTester() { super("I'm leaky"); add(new JLabel("Drop stuff here")); setTransferHandler(new TransferHandler() { @Override public boolean canImport(final TransferSupport support) { return (support.isDrop() && support .isDataFlavorSupported(DataFlavor.javaFileListFlavor)); } @Override public boolean importData(final TransferSupport support) { if (!canImport(support)) { return false; } try { final List<File> files = (List<File>) support.getTransferable().getTransferData(DataFlavor.javaFileListFlavor); for (final File f : files) { System.out.println(f.getName()); } } catch (Exception e) { e.printStackTrace(); } return true; } }); setDefaultCloseOperation(DISPOSE_ON_CLOSE); pack(); setVisible(true); } } To reproduce, run the code and drop some files on the frame. Close the frame so it's disposed of. To verify the leak I take a heap dump using JConsole and analyse it with the Eclipse Memory Analysis tool. It shows that sun.awt.AppContext is holding a reference to the frame through its hashmap. It looks like TransferSupport is at fault. What am I doing wrong? Should I be asking the DnD support code to clean itself up somehow? I'm running JDK 1.6 update 19.

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• Cepstral Analysis for pitch detection

  - by Ohmu

  Hi! I'm looking to extract pitches from a sound signal. Someone on IRC just explain to me how taking a double FFT achieves this. Specifically: take FFT take log of square of absolute value (can be done with lookup table) take another FFT take absolute value I am attempting this using vDSP I can't understand how I didn't come across this technique earlier. I did a lot of hunting and asking questions; several weeks worth. More to the point, I can't understand why I didn't think of it. I am attempting to achieve this with vDSP library. it looks as though it has functions to handle all of these tasks. However, I'm wondering about the accuracy of the final result. I have previously used a technique which scours the frequency bins of a single FFT for local maxima. when it encounters one, it uses a cunning technique (the change in phase since the last FFT) to more accurately place the actual peak within the bin. I am worried that this precision will be lost with this technique I'm presenting here. I guess the technique could be used after the second FFT to get the fundamental accurately. But it kind of looks like the information is lost in step 2. as this is a potentially tricky process, could someone with some experience just look over what I'm doing and check it for sanity? also, I've heard there is an alternative technique involving fitting a quadratic over neighbouring bins. Is this of comparable accuracy? if so, I would favour it, as it doesn't involve remembering bin phases. so questions: does this approach makes sense? Can it be improved? I'm a bit worried about And the log square component; there seems to be a vDSP function to do exactly that: vDSP_vdbcon however, there is no indication it precalculates a log-table -- I assume it doesn't, as the FFT function requires an explicit pre-calculation function to be called and passed into it. and this function doesn't. Is there some danger of harmonics being picked up? is there any cunning way of making vDSP pull out the maxima, biggest first? Can anyone point me towards some research or literature on this technique? the main question: is it accurate enough? Can the accuracy be improved? I have just been told by an expert that the accuracy IS INDEED not sufficient. Is this the end of the line? Pi PS I get SO annoyed (npi) when I want to create tags, but cannot. :| I have suggested to the maintainers that SO keep track of attempted tags, but I'm sure I was ignored. we need tags for vDSP, accelerate framework, cepstral analysis

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• What would you suggest as a high school first language?

  - by ldigas

  Edit by OA: After reading some answers I'll just update the question a little. At first I put it a little bluntly, but some of those gave me some good arguments which have to be taken into consideration while making a stand on this one. (these are mostly picked up from comments and answers below). A few things to take into account: to many pupils this is a first programming language - at this stage most of them have trouble grasping a difference between data types, variable passing, ... and whatnot, less alone pointers and similar 'low level stuff' :) they will all have to pass this to get into next grade (well, big majority of them anyway) not all of them have computers at home, not all of them are willing to learn this, less alone interested in - so the concepts have to be taught on a finite time scale in school hours (as well as practice on computers) free literature is a bonus - the teacher will make some scripts and handaways, but still ... I wouldn't like to bear the parents with the burden of buying expensive literature (also, english is not a native language here ... and although they are all learning it, their ability to read it fluently is somewhat questionable) somebody gave an argument - "a language which does not get in the way of ideas" - good one accessibility on different platforms in not expecially important at this point - although most of the suggested ones are available on win as well as linux - not many macs in this part of europe (their prices are sky high for anything but specialised usage) I will check what are the licencing issues on ms express editions about using it massively in high schools for purposes like this - if someone has any info about this, please, do not be shy with it :) A friend of mine, informatics teacher - in EU it comes as something as junior cs teacher, in a local high school asked me what I thought about what should be the first language pupils should be taught? It is a technical school (a little more oriented towards mathematics than the gymnasium, but not computer oriented totally). So I'm asking you - what do you think should be the first language pupils are exposed to in highschool? They have been teaching Pascal so far, but she's not sure that's a good course. She thought about switching to C (which I resented; considering not all pupils have interests in programming, to start with, and should be taught something higher level since they are just gripping the idea of a loop and such ... for a start), I suggested python or ruby (preferably py since it handles all paradigms). What is your opinion on this one? I looked, but didn't find a similar question on SO, so if there is one, please just point me towards it. Edit: The assumption is that none of the pupils have been exposed to any programming in junior school. See also: What is the best way to teach young kids some basic programming concepts? Best ways to teach a beginner to program How and when do you teach a kid to code What is the easiest language to start with? High School Programming

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• C++ program Telephone Directory from a file

  - by Stacy Doyle

  I am writing a program for a phone directory. The user inputs a name and the program searches the file and either outputs the number or an error because the persons name is not in the file. The program should also ask the user if they would like to continue using the program and look up another number. So far runs and asks for the name and then prints the error message that I put in place saying that the name is not in the database. I am guessing that I must not really be having my program look in the file but not sure what to do also don't know how to get the program to run again if the user chooses to continue. #include <iostream> #include <fstream> #include <string> #include <iomanip> using namespace std; char chr; int main() { string first; string last; string number; string firstfile; string lastfile; string numberfile; int cont; ifstream infile; infile.open("name and numbers.dat"); //opening the file infile>>firstfile>>lastfile>>numberfile; cout<<"Enter a first and last name."<<endl; //Asking user for the input cin>>first>>last; //input the data { if(first==firstfile && last==lastfile) //if the entered information matches the information in the file cout<<first<<" "<<last<<"'s number is "<<numberfile<<endl; //this is printed else cout<<"Sorry that is not in our database."<<endl; //if the information doesn't match this is printed } cout<<"Would you like to search for another name? Y or N"<<endl; //user is asked if they would like to continue cin>>cont; infile.close(); //close file cin>>chr; return 0; }

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• approximating log10[x^k0 + k1]

  - by Yale Zhang

  Greetings. I'm trying to approximate the function Log10[x^k0 + k1], where .21 < k0 < 21, 0 < k1 < ~2000, and x is integer < 2^14. k0 & k1 are constant. For practical purposes, you can assume k0 = 2.12, k1 = 2660. The desired accuracy is 5*10^-4 relative error. This function is virtually identical to Log[x], except near 0, where it differs a lot. I already have came up with a SIMD implementation that is ~1.15x faster than a simple lookup table, but would like to improve it if possible, which I think is very hard due to lack of efficient instructions. My SIMD implementation uses 16bit fixed point arithmetic to evaluate a 3rd degree polynomial (I use least squares fit). The polynomial uses different coefficients for different input ranges. There are 8 ranges, and range i spans (64)2^i to (64)2^(i + 1). The rational behind this is the derivatives of Log[x] drop rapidly with x, meaning a polynomial will fit it more accurately since polynomials are an exact fit for functions that have a derivative of 0 beyond a certain order. SIMD table lookups are done very efficiently with a single _mm_shuffle_epi8(). I use SSE's float to int conversion to get the exponent and significand used for the fixed point approximation. I also software pipelined the loop to get ~1.25x speedup, so further code optimizations are probably unlikely. What I'm asking is if there's a more efficient approximation at a higher level? For example: Can this function be decomposed into functions with a limited domain like log2((2^x) * significand) = x + log2(significand) hence eliminating the need to deal with different ranges (table lookups). The main problem I think is adding the k1 term kills all those nice log properties that we know and love, making it not possible. Or is it? Iterative method? don't think so because the Newton method for log[x] is already a complicated expression Exploiting locality of neighboring pixels? - if the range of the 8 inputs fall in the same approximation range, then I can look up a single coefficient, instead of looking up separate coefficients for each element. Thus, I can use this as a fast common case, and use a slower, general code path when it isn't. But for my data, the range needs to be ~2000 before this property hold 70% of the time, which doesn't seem to make this method competitive. Please, give me some opinion, especially if you're an applied mathematician, even if you say it can't be done. Thanks.

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• How to Work Around Limitations in Generic Type Constraints in C#?

  - by Jose

  Okay I'm looking for some input, I'm pretty sure this is not currently supported in .NET 3.5 but here goes. I want to require a generic type passed into my class to have a constructor like this: new(IDictionary<string,object>) so the class would look like this public MyClass<T> where T : new(IDictionary<string,object>) { T CreateObject(IDictionary<string,object> values) { return new T(values); } } But the compiler doesn't support this, it doesn't really know what I'm asking. Some of you might ask, why do you want to do this? Well I'm working on a pet project of an ORM so I get values from the DB and then create the object and load the values. I thought it would be cleaner to allow the object just create itself with the values I give it. As far as I can tell I have two options: 1) Use reflection(which I'm trying to avoid) to grab the PropertyInfo[] array and then use that to load the values. 2) require T to support an interface like so: public interface ILoadValues { void LoadValues(IDictionary values); } and then do this public MyClass<T> where T:new(),ILoadValues { T CreateObject(IDictionary<string,object> values) { T obj = new T(); obj.LoadValues(values); return obj; } } The problem I have with the interface I guess is philosophical, I don't really want to expose a public method for people to load the values. Using the constructor the idea was that if I had an object like this namespace DataSource.Data { public class User { protected internal User(IDictionary<string,object> values) { //Initialize } } } As long as the MyClass<T> was in the same assembly the constructor would be available. I personally think that the Type constraint in my opinion should ask (Do I have access to this constructor? I do, great!) Anyways any input is welcome.

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• How would you implement this "WorkerChain" functionality in .NET?

  - by Dan Tao

  Sorry for the vague question title -- not sure how to encapsulate what I'm asking below succinctly. (If someone with editing privileges can think of a more descriptive title, feel free to change it.) The behavior I need is this. I am envisioning a worker class that accepts a single delegate task in its constructor (for simplicity, I would make it immutable -- no more tasks can be added after instantiation). I'll call this task T. The class should have a simple method, something like GetToWork, that will exhibit this behavior: If the worker is not currently running T, then it will start doing so right now. If the worker is currently running T, then once it is finished, it will start T again immediately. GetToWork can be called any number of times while the worker is running T; the simple rule is that, during any execution of T, if GetToWork was called at least once, T will run again upon completion (and then if GetToWork is called while T is running that time, it will repeat itself again, etc.). Now, this is pretty straightforward with a boolean switch. But this class needs to be thread-safe, by which I mean, steps 1 and 2 above need to comprise atomic operations (at least I think they do). There is an added layer of complexity. I have need of a "worker chain" class that will consist of many of these workers linked together. As soon as the first worker completes, it essentially calls GetToWork on the worker after it; meanwhile, if its own GetToWork has been called, it restarts itself as well. Logically calling GetToWork on the chain is essentially the same as calling GetToWork on the first worker in the chain (I would fully intend that the chain's workers not be publicly accessible). One way to imagine how this hypothetical "worker chain" would behave is by comparing it to a team in a relay race. Suppose there are four runners, W1 through W4, and let the chain be called C. If I call C.StartWork(), what should happen is this: If W1 is at his starting point (i.e., doing nothing), he will start running towards W2. If W1 is already running towards W2 (i.e., executing his task), then once he reaches W2, he will signal to W2 to get started, immediately return to his starting point and, since StartWork has been called, start running towards W2 again. When W1 reaches W2's starting point, he'll immediately return to his own starting point. If W2 is just sitting around, he'll start running immediately towards W3. If W2 is already off running towards W3, then W2 will simply go again once he's reached W3 and returned to his starting point. The above is probably a little convoluted and written out poorly. But hopefully you get the basic idea. Obviously, these workers will be running on their own threads. Also, I guess it's possible this functionality already exists somewhere? If that's the case, definitely let me know!

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• How do you combine "Revision Control" with "WorkFlow" for R?

  - by Tal Galili

  Hello all, I remember coming across R users writing that they use "Revision control" (e.g: "Source control"), and I am curious to know: How do you combine "Revision control" with your statistical analysis WorkFlow? Two (very) interesting discussions talk about how to deal with the WorkFlow. But neither of them refer to the revision control element: http://stackoverflow.com/questions/1266279/how-to-organize-large-r-programs http://stackoverflow.com/questions/1429907/workflow-for-statistical-analysis-and-report-writing A Long Update To The Question: Following some of the people's answers, and Dirk's question in the comment, I would like to direct my question a bit more. After reading the Wiki article about "revision control" (which I was previously not familiar with), it was clear to me that when using revision control, what one does is to build a development structure of his code. This structure either leads to a "final product" or to several branches. When building something like, let's say, a website. There is usually one end product you work towards (the website), with some prototypes along the way. But when doing a statistical analysis, the work (to my view) is different. Sometimes you know where you want to get to. But more often, you explore. Explore cleaning the dataset. Explore different methods for statistical analysis, and ask various questions of your data (and I am writing this, knowing how Frank Harrell, and other experience statisticians feels about Data dredging). That is way the WorkFlow question with statistical programming is (in my view) a serious and deep question, raising many issues, The simpler ones are technical: Which revision control software do you use (and why) ? Which IDE do you use(and why) ? The more interesting question are about work process: How do you structure your files? What do you keep as a separate file and what as a revision? or asking in a different way - What should be a "branch" and what should be a "sub project" in your code? For example: When starting to explore your data, should a plot be creating and then erased because it didn't lead any where (but kept as a revision) or should there be a backup file of that path? How you solve this tension was my initial curiosity. The second question is "what might I be missing?". What rules (of thumb) should one follow so to avoid common pitfalls doing statistical programming with version control? In my intuition, I feel that statistical programming is inherently different then software development (I am writing this without being a real expert in statistical programming, and even less so in software development). That's way I am unsure which of the lessons I have read here about version control would be applicable. Thanks a lot, Tal

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• Generic Type constraint in .net

  - by Jose

  Okay I'm looking for some input, I'm pretty sure this is not currently supported in .NET 3.5 but here goes. I want to require a generic type passed into my class to have a constructor like this: new(IDictionary<string,object>) so the class would look like this public MyClass<T> where T : new(IDictionary<string,object>) { T CreateObject(IDictionary<string,object> values) { return new T(values); } } But the compiler doesn't support this, it doesn't really know what I'm asking. Some of you might ask, why do you want to do this? Well I'm working on a pet project of an ORM so I get values from the DB and then create the object and load the values. I thought it would be cleaner to allow the object just create itself with the values I give it. As far as I can tell I have two options: 1) Use reflection(which I'm trying to avoid) to grab the PropertyInfo[] array and then use that to load the values. 2) require T to support an interface like so: public interface ILoadValues { void LoadValues(IDictionary values); } and then do this public MyClass<T> where T:new(),ILoadValues { T CreateObject(IDictionary<string,object> values) { T obj = new T(); obj.LoadValues(values); return obj; } } The problem I have with the interface I guess is philosophical, I don't really want to expose a public method for people to load the values. Using the constructor the idea was that if I had an object like this namespace DataSource.Data { public class User { protected internal User(IDictionary<string,object> values) { //Initialize } } } As long as the MyClass<T> was in the same assembly the constructor would be available. I personally think that the Type constraint in my opinion should ask (Do I have access to this constructor? I do, great!) Anyways any input is welcome.

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• How to calculate the maximum block length in C of a binary number

  - by user1664272

  I want to reiterate the fact that I am not asking for direct code to my problem rather than wanting information on how to reach that solution. I asked a problem earlier about counting specific integers in binary code. Now I would like to ask how one comes about counting the maximum block length within binary code. I honestly just want to know where to get started and what exactly the question means by writing code to figure out the "Maximum block length" of an inputted integers binary representation. Ex: Input 456 Output: 111001000 Number of 1's: 4 Maximum Block Length: ? Here is my code so far for reference if you need to see where I'm coming from. #include <stdio.h> int main(void) { int integer; // number to be entered by user int i, b, n; unsigned int ones; printf("Please type in a decimal integer\n"); // prompt fflush(stdout); scanf("%d", &integer); // read an integer if(integer < 0) { printf("Input value is negative!"); // if integer is less than fflush(stdout); return; // zero, print statement } else{ printf("Binary Representation:\n", integer); fflush(stdout);} //if integer is greater than zero, print statement for(i = 31; i >= 0; --i) //code to convert inputted integer to binary form { b = integer >> i; if(b&1){ printf("1"); fflush(stdout); } else{ printf("0"); fflush(stdout); } } printf("\n"); fflush(stdout); ones = 0; //empty value to store how many 1's are in binary code while(integer) //while loop to count number of 1's within binary code { ++ones; integer &= integer - 1; } printf("Number of 1's in Binary Representation: %d\n", ones); // prints number fflush(stdout); //of ones in binary code printf("Maximum Block Length: \n"); fflush(stdout); printf("\n"); fflush(stdout); return 0; }//end function main

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• Patterns: Local Singleton vs. Global Singleton?

  - by Mike Rosenblum

  There is a pattern that I use from time to time, but I'm not quite sure what it is called. I was hoping that the SO community could help me out. The pattern is pretty simple, and consists of two parts: A singleton factory, which creates objects based on the arguments passed to the factory method. Objects created by the factory. So far this is just a standard "singleton" pattern or "factory pattern". The issue that I'm asking about, however, is that the singleton factory in this case maintains a set of references to every object that it ever creates, held within a dictionary. These references can sometimes be strong references and sometimes weak references, but it can always reference any object that it has ever created. When receiving a request for a "new" object, the factory first searches the dictionary to see if an object with the required arguments already exits. If it does, it returns that object, if not, it returns a new object and also stores a reference to the new object within the dictionary. This pattern prevents having duplicative objects representing the same underlying "thing". This is useful where the created objects are relatively expensive. It can also be useful where these objects perform event handling or messaging - having one object per item being represented can prevent multiple messages/events for a single underlying source. There are probably other reasons to use this pattern, but this is where I've found this useful. My question is: what to call this? In a sense, each object is a singleton, at least with respect to the data it contains. Each is unique. But there are multiple instances of this class, however, so it's not at all a true singleton. In my own personal terminology, I tend to call the factory method a "global singleton". I then call the created objects "local singletons". I sometimes also say that the created objects have "reference equality", meaning that if two variables reference the same data (the same underlying item) then the reference they each hold must be to the same exact object, hence "reference equality". But these are my own invented terms, and I am not sure that they are good ones. Is there standard terminology for this concept? And if not, could some naming suggestions be made? Thanks in advance...

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• Passing password value through URL

  - by Steven Wright

  OK I see a lot of people asking about passing other values, URLS, random stuff through a URL, but don't find anything about sending a password to a password field. Here is my situation: I have a ton of sites I use on a daily basis with my work and oh about 90% require logins. Obviously remembering 80 bajillion logins for each site is dumb, especially when there are more than one user name I use for each site. So to make life easier, I drew up a nifty JSP app that stores all of my logins in a DB table and creates a user interface for the specific page I want to visit. Each page has a button that sends a username, password into the id parameters of the html inputs. Problem: I can get the usernames and other info to show up just dandy, but when I try and send a password to a password field, it seems that nothing gets received by the page I'm trying to hit. Is there some ninja stuff I need to be doing here or is it just not easily possible? Basically this is what I do now: http://addresshere/support?loginname=steveoooo&loginpass=passwordhere and some of my html looks like this: <form name="userform" method="post" action="index.jsp" > <input type="hidden" name="submit_login" value="y"> <table width="100%"> <tr class="main"> <td width="100" nowrap>Username:</td> <td><input type="text" name="loginname" value="" size="30" maxlength="64"></td> </tr> <tr class="main"> <td>Password: </font></td> <td><input type="password" name="loginpass" value="" size="30" maxlength="64"></td> </tr> <tr class="main"> <td><center><input type="submit" name="submit" value="Login"></center></td> </tr> </table> </form> Any suggestions?

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• java instanceof not finding method

  - by Razvan N

  I have a problem with java instanceof. I have a class called Employee and several others that extend this one, for example - Manager. I also created another class,EmployeeStockPlan, where I wanted to test if instanceof is finding which object I am using. But when I am calling a method from the new class, I have this error: The method grantStock(Manager) is undefined for the type Loader. Sorry, I am somehow new to some thing in java, I hope I am not asking dumb questions. The Employee class: package com.example.domain; public class Employee { private int empId; private String name; private String ssn; private double salary; public Employee(int empId, String name, String ssn, double salary) { // constructor // method; this.empId = empId; this.name = name; this.ssn = ssn; this.salary = salary; } public void setName(String newName) { if (newName != null) { this.name = newName; } } public void raiseSalary(double increase) { this.salary += increase; } public String getName() { return name; } public double getSalary() { return salary; } public String getDetails() { return "Employee id: " + empId + "\n" + "Employee name: " + name; } } The Manager class: package com.example.domain; public class Manager extends Employee { private String deptName; public Manager(int empId, String name, String ssn, double salary, String dept) { super(empId, name, ssn, salary); this.deptName = dept; } public String getDeptName() { return deptName; } public String getDetails() { return super.getDetails() + "\n" + "Department: " + deptName; } } The EmployeeStockPlan class: package com.example.domain; public class EmployeeStockPlan { public void grantStock(Employee e) { // nothing calculated, just simulating; System.out.println("This is an employee!"); if (e instanceof Manager) { // process Manager stock grant System.out.println("This is a manager!"); } else { // error - instance of Engineer? System.out.println("Not an engineer!"); } return; } } The main class: EmployeeStockPlan esp = new EmployeeStockPlan(); Manager m = new Manager (12421, "Manager1", "111-4254-521", 2430, "Marketing1"); grantStock(m);

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• Question about POP3 message termination octet

  - by user361633

  This is from the POP3 RFC. "Responses to certain commands are multi-line. In these cases, which are clearly indicated below, after sending the first line of the response and a CRLF, any additional lines are sent, each terminated by a CRLF pair. When all lines of the response have been sent, a final line is sent, consisting of a termination octet (decimal code 046, ".") and a CRLF pair. If any line of the multi-line response begins with the termination octet, the line is "byte-stuffed" by pre-pending the termination octet to that line of the response. Hence a multi-line response is terminated with the five octets "CRLF.CRLF". When examining a multi-line response, the client checks to see if the line begins with the termination octet. If so and if octets other than CRLF follow, the first octet of the line (the termination octet) is stripped away. If so and if CRLF immediately follows the termination character, then the response from the POP server is ended and the line containing ".CRLF" is not considered part of the multi-line response." Well, i have problem with this, for example gmail sometimes sends the termination octet and then in the NEXT LINE sends the CRLF pair. For example: "+OK blah blah" "blah blah." "\r\n" That's very rare, but it happens sometimes, so obviously i'm unable to determine the end of the message in such case, because i'm expecting a line that consists of '.\r\n'. Seriously, is Gmail violating the POP3 protocol or i'm doing something wrong? Also i have a second question, english is not my first language so i cannot understand that completely: "If any line of the multi-line response begins with the termination octet, the line is "byte-stuffed" by pre-pending the termination octet to that line of the response. Hence a multi-line response is terminated with the five octets "CRLF.CRLF"." When exactly CRLF.CRLF is used? Can someone gives me a simple example? The rfc says that is used when any line of the response begins with the termination octet. But i don't see any lines that starts with '.' in the messages that are terminated with CRLF.CRLF. I checked that. Maybe i don't understand something, that's why i'm asking.

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• jquery show hidden div

  - by Fahad

  Firstly, I'm sort of embarrassed asking about this, so many people have already asked this question but even after having gone through so many posts, I'm unable to achieve what I want. Basically, a div, initially hidden, has to be displayed on a button click. I tried hiding the div using display:none and hide() and then displaying it using show(), toggle(), and css("display","block"). Using all sorts of combinations of the above, I was still unable to get the result. Code: <html xmlns="http://www.w3.org/1999/xhtml"> <head runat="server"> <title></title> <link href="css/smoothness/jquery-ui-1.9.2.custom.min.css" rel="stylesheet" type="text/css" /> <script src="jQuery/jquery-1.8.3.min.js" type="text/javascript"></script> <script src="jQuery/jquery-ui-1.9.2.custom.min.js" type="text/javascript"></script> <script type="text/javascript"> $(document).ready(function () { $('#one').hide(); $('#Button1').click(function () { $('#one').toggle(500); }); }); </script> </head> <body> <form id="form1" runat="server"> <div id="one" style="height: 20px;width:200px; background-color: Red; "> </div> <asp:Button ID="Button1" runat="server" Text="Show" /> </form> </body> </html> On button click, the div is shown for a brief second before it disappears again. The same thing happens if I use show() instead of toggle() in the above code. Again the same thing if I set style="display:none" to the div instead of using hide() and then use show() or toggle(). I also tried using $('#one').css("display","block"); but again, the same result. Can anyone please tell me where I'm going wrong. Just started learning jQuery and it is really frustrating when something apparently so simple will not work. Thanks in advance. :)

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