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  • How would you code an efficient Circular Buffer in Java or C#

    - by Cheeso
    I want a simple class that implements a fixed-size circular buffer. It should be efficient, easy on the eyes, generically typed. EDIT: It need not be MT-capable, for now. I can always add a lock later, it won't be high-concurrency in any case. Methods should be: .Add and I guess .List, where I retrieve all the entries. On second thought, Retrieval I think should be done via an indexer. At any moment I will want to be able to retrieve any element in the buffer by index. But keep in mind that from one moment to the next Element[n] may be different, as the Circular buffer fills up and rolls over. This isn't a stack, it's a circular buffer. Regarding "overflow": I would expect internally there would be an array holding the items, and over time the head and tail of the buffer will rotate around that fixed array. But that should be invisible from the user. There should be no externally-detectable "overflow" event or behavior. This is not a school assignment - it is most commonly going to be used for a MRU cache or a fixed-size transaction or event log.

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  • Mysql partitioning: Partitions outside of date range is included

    - by Sturlum
    Hi, I have just tried to configure partitions based on date, but it seems that mysql still includes a partition with no relevant data. It will use the relevant partition but also include the oldest for some reason. Am I doing it wrong? The version is 5.1.44 (MyISAM) I first added a few partitions based on "day", which is of type "date" ALTER TABLE ptest PARTITION BY RANGE(TO_DAYS(day)) ( PARTITION p1 VALUES LESS THAN (TO_DAYS('2009-08-01')), PARTITION p2 VALUES LESS THAN (TO_DAYS('2009-11-01')), PARTITION p3 VALUES LESS THAN (TO_DAYS('2010-02-01')), PARTITION p4 VALUES LESS THAN (TO_DAYS('2010-05-01')) ); After a query, I find that it uses the "old" partition, that should not contain any relevant data. mysql> explain partitions select * from ptest where day between '2010-03-11' and '2010-03-12'; +----+-------------+------------+------------+-------+---------------+------+---------+------+------+-------------+ | id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | Extra | +----+-------------+------------+------------+-------+---------------+------+---------+------+------+-------------+ | 1 | SIMPLE | ptest | p1,p4 | range | day | day | 3 | NULL | 79 | Using where | +----+-------------+------------+------------+-------+---------------+------+---------+------+------+-------------+ When I select a single day, it works: mysql> explain partitions select * from ptest where day = '2010-03-11'; +----+-------------+------------+------------+------+---------------+------+---------+-------+------+-------+ | id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | Extra | +----+-------------+------------+------------+------+---------------+------+---------+-------+------+-------+ | 1 | SIMPLE | ptest | p4 | ref | day | day | 3 | const | 39 | | +----+-------------+------------+------------+------+---------------+------+---------+-------+------+-------+

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  • FFT and IFFT on 3D matrix (Matlab)

    - by SteffenDM
    I have a movie with 70 grayscale frames in MATLAB. I have put them in a 3-D matrix, so the dimensions are X, Y and time. I want to determine the frequencies in the time dimension, so I have to calculate the FFT for every point in the 3rd dimension. This is not a problem but I have to return the images to the original form with ifft. In a normal situation this would be true: X = ifft(fft(X)), but this is not the case it seems in MATLAB when you work with multidimensional data. This is the code I use: for i = 1:length y(:, :, i) = [img1{i, level}]; %# take each picture from an cell array and put it end %# and put it in 3D array y2 = ifft(fft(y, NFFT,3), NFFT, 3); %# NFFT = 128, the 3 is the dimension in which i want %# to calculate the FFT and IFFT y is 480x640x70, so there are 70 images of 640x480 pixels. If I use only fft, y2 is 480x640x128 (this is normal because we want 128 points with NFFT). If I use fft and ifft, y2 is 480x640x128 pixels. This is not normal, the 128 should be 70 again. I tried to do it in just one dimension by using 2 for loops and this works fine. The for loops take to much time, though.

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  • All symbols after & stripped

    - by user300413
    My query: mysql::getInstance()->update('requests', array('response' => mysql_real_escape_string($_POST['status'])), array('secret' => $_POST['secret'])); ?> If i wand to add string with "&" symbol, all symbols after "&" stripped. Example: string: !"?;%:?*()_+!@#$%^&*()_+ in database i see only: !"?;%:?*()_+!@#$%^ How to fix this? update function, if anyone need: function update($table, $updateList, $whereConditions) { $updateQuery = ''; foreach ($updateList as $key => $newValue) { if (!is_numeric($newValue)) { $newValue = "'" . $newValue . "'"; } if (strlen($updateQuery) == 0) { $updateQuery .= '`' . $key . '` = ' . $newValue; } else { $updateQuery .= ', `' . $key . '` = ' . $newValue; } } return $this->query('UPDATE ' . $table . ' SET ' . $updateQuery . $this->buildWhereClause($whereConditions)); }

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  • NSTableView don't display data

    - by Tomas Svoboda
    HI, I have data in NSMutableArray and I want to display it in NSTableView, but only the number of cols has changed. This use of NSTableView is based on tutorial: http://www.youtube.com/watch?v=5teN5pMf-rs FinalImageBrowser is IBOutlet to NSTableView @implementation AppController NSMutableArray *listData; - (void)awakeFromNib { [FinalImageBrowser setDataSource:self]; } - (IBAction)StartReconstruction:(id)sender { NSMutableArray *ArrayOfFinals = [[NSMutableArray alloc] init]; //Array of list with final images NSString *FinalPicture; NSString *PicNum; int FromLine = [TextFieldFrom intValue]; //read number of start line int ToLine = [TextFieldTo intValue]; //read number of finish line int RecLine; for (RecLine = FromLine; RecLine < ToLine; RecLine++) //reconstruct from line to line { Start(RecLine); //start reconstruction //Create path of final image FinalPicture = @"FIN/final"; PicNum = [NSString stringWithFormat: @"%d", RecLine]; FinalPicture = [FinalPicture stringByAppendingString:PicNum]; FinalPicture = [FinalPicture stringByAppendingString:@".bmp"]; [ArrayOfFinals addObject:FinalPicture]; // add path to array } listData = [[NSMutableArray alloc] init]; [listData autorelease]; [listData addObjectsFromArray:ArrayOfFinals]; [FinalImageBrowser reloadData]; NSBeep(); //make some noise NSImage *fin = [[NSImage alloc] initWithContentsOfFile:FinalPicture]; [FinalImage setImage:fin]; } - (int)numberOfRowsInTableView:(NSTableView *)tv { return [listData count]; } - (id)tableView:(NSTableView *)tv objectValueFromTableColumn:(NSTableColumn *)tableColumn row:(int)row { return (NSString *)[listData objectAtIndex:row]; } @end when the StartReconstruction end the number of cols have changed right, but they're empty. When I debug app, items in listData is rigth. Thanks

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  • The Current State Of Serving a PHP 5.x App on the Apache, LightTPD & Nginx Web Servers?

    - by Gregory Kornblum
    Being stuck in a MS stack architecture/development position for the last year and a half has prevented me from staying on top of the world of open source stack based web servers recent evolution more than I would have liked to. However I am now building an open source stack based application/system architecture and sadly I do not have the time to give each of the above mentioned web servers a thorough test of my own to decide. So I figured I'd get input from the best development community site and more specifically the people who make it so. This is a site that is a resource for information regarding a specific domain and target audience with features to help users not only find the information but to also interact with one another in various ways for various reasons. I chose the open source stack for the wealth of resources it has along with much better offers than the MS stack (i.e. WordPress vs BlogEngine.NET). I feel Java is more in the middle of these stacks in this regard although I am not ruling out the possibility of using it in certain areas unrelated to the actual web app itself such as background processes. I have already come to the conclusion of using PHP (using CodeIgniter framework & APC), MySQL (InnoDB) and Memcached on CentOS. I am definitely serving static content on Nginx. However the 3 servers mentioned have no consensus on which is best for dynamic content in regards to performance. It seems LightTPD still has the leak issue which rules it out if it does, Nginx seems it is still not mature enough for this aspect and of course Apache tries to be everything for everybody. I am still going to compile the one chosen with as many performance tweaks as possible such as static linking and the likes. I believe I can get Apache to match the other 2 in regards to serving dynamic content through this process and not having it serve anything static. However during my research it seems the others are still worth considering. So with all things considered I would love to hear what everyone here has to say on the matter. Thanks!

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  • Populating a Datagrid with variable number of columns and rows in Flex

    - by Rie Mino
    I am trying to figure out how to manage a Datagrid based on an XML object like this: <matrix rows="5" columns="5"> <column> <row>0.5</row> <row>0.21</row> </column> <column> <row>0.6</row> <row>0.9</row> </column> <column> <row>0.5</row> <row>0.5</row> </column> <column> <row>0.8</row> <row>0.4</row> </column> </matrix> I will need to populate the Datagrid column names based on a different XML object and use the above XML to populate each of the column's rows. I currently am able to create the Datagrid and populate its column headers but I am unsure as to how to how to add the rows for each column. The above XML will be update with new row and column elements added and deleted. This, of course, will be bound to the Datagrid to show updates. Thanks in advanced for your help.

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  • Using an SHA1 with Micrsoft CAPI

    - by Erik Jõgi
    Hello, I have an SHA1 hash and I need to sign it. The CryptSignHash() method requires a HCRYPTHASH handle for signing. I create it and as I have the actual hash value already then set it: CryptCreateHash(cryptoProvider, CALG_SHA1, 0, 0, &hash); CryptSetHashParam(hash, HP_HASHVAL, hashBytes, 0); The hashBytes is an array of 20 bytes. However the problem is that the signature produced from this HCRYPTHASH handle is incorrect. I traced the problem down to the fact that CAPI actually doesn't use all 20 bytes from my hashBytes array. For some reason it thinks that SHA1 is only 4 bytes. To verify this I wrote this small program: HCRYPTPROV cryptoProvider; CryptAcquireContext(&cryptoProvider, NULL, NULL, PROV_RSA_FULL, 0); HCRYPTHASH hash; HCRYPTKEY keyForHash; CryptCreateHash(cryptoProvider, CALG_SHA1, keyForHash, 0, &hash); DWORD hashLength; CryptGetHashParam(hash, HP_HASHSIZE, NULL, &hashLength, 0); printf("hashLength: %d\n", hashLength); And this prints out hashLength: 4 ! Can anyone explain what I am doing wrong or why Microsoft CAPI thinks that SHA1 is 4 bytes (32 bits) instead of 20 bytes (160 bits). Thank you.

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  • Objective C map view delegate viewForAnnotation for MKAnnotation gets just called after click

    - by user1185486
    I have a simple Map view. It has a method -(void)loadAndDisplayPois{ NSLog(@"loadAndDisplayPois"); if(mapView.annotations.count > 0) [mapView removeAnnotations:mapView.annotations]; self.pois = [self loadPoisFromDatabase]; NSLog(@"self.pois.count: %i", self.pois.count); [mapView addAnnotations:self.pois]; NSLog(@"mapView.annotations.count: %i",mapView.annotations.count);} This method gets called, and I am sure that the method gets called because of the Log, after I downloaded data and saved it into the database. The class which handles the download executes after saving the data to the database [self.senderObj performSelector:@selector(loadAndDisplayPois)]; Where senderObj is the MapViewControlller. The count Log from the pois array shows 4 after the first time I clicked. But no Annotations on the view, because viewForAnnotation is not called (one Annotation in the array ( my current position)). After I execute the method again by clicking a TEST button shows everything on the map. The viewForAnnotation method gets called after viewWillAppear and after I clicked the TEST button. It is driving me nuts since 2 days. I cant anymore ...

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  • How can I evaluate the connectedness of my nodes?

    - by Travis Leleu
    I've got a space that has nodes that are all interconnected, based on a "similarity score". I would like to determine how "connected" a node is with the others. My purpose is to find nodes that are poorly connected to make sure that the backlink from the other node is prioritized. Perhaps an example would help. I've got a web page that links to my other pages based on a similarity score. Suppose I have the pages: A, B, C, ... A has a backlink from every other page, so it's very well connected. It also has links to all my other pages (each line in the graph is essentially bidirectional). B only has 1 backlink, from A. C has a link from A and D. I would like to make sure that the A-B link is prioritized over the A-C link (even if the similarity score between C and A is higher than B and A). In short, I would like to evaluate which nodes are least and best connected, so that I can mangle the results to my means. I believe this is Graph Connectedness, but I'm at a loss to develop a (simple) algorithm that will help me here. Simply counting the backlinks to a node may be a starting point -- but then how do I take the next step, which is to properly weight the links on the original node (A, in the example above)?

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  • explode is not working to split string

    - by pmms
    we unable to split the string following code.please Help us. <?php $i=0; $myFile = "testFile.txt"; $fh = fopen($myFile, 'a') or die("can't open file"); $stringData = "no\t"; fwrite($fh, $stringData); $stringData = "username \t"; fwrite($fh, $stringData); $stringData ="password \t"; fwrite ($fh,$stringData); $newline ="\r\n"; fwrite ($fh,$newline); $stringData1 = "1\t"; fwrite($fh, $stringData1); $stringData1 = "srinivas \t"; fwrite($fh, $stringData1); $stringData1 ="malayappa \t"; fwrite ($fh,$stringData1); fclose($fh); ?> $fh = fopen("testFile.txt", "r"); $ while (!feof($fh)) { $line = fgets($fh); echo $line; } fclose($fh); $Beatles = array('pmm','malayappa','sreenivas','PHP'); for($i=0;$i<count($Beatles);$i++) { if($i==2) { echo $Beatles[$i-1]; echo $Beatles[$i-2]; } } $pass_ar=array(); $fh = fopen("testFile.txt", "r"); while (!feof($fh)) { $line = fgets($fh); echo $line; $t1=explode(" ",$line); print_r($t1); array_push($pass_ar,t1); } fclose($fh); Thanks & Regards pmms

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  • How do I pass an NSString through 3 ViewControllers?

    - by dBloc
    hey, I'm currently using the iPhone SDK and I'm having trouble passing an NSString through 3 views I am able to pass an NSString between 2 view controllers but I am unable to pass it through another one. My code is as follows... `- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)index`Path { NSString *string1 = nil; NSDictionary *dictionary = [listOfItems objectAtIndex:indexPath.section]; NSArray *array = [dictionary objectForKey:@"items"]; string1 = [array objectAtIndex:indexPath.row]; //Initialize the detail view controller and display it. ViewController2 *vc2 = [[ViewController2 alloc] initWithNibName:@"ViewController2" bundle:[NSBundle mainBundle]]; vc2.string1 = string1; [self.navigationController pushViewController:vc2 animated:YES]; [vc2 release]; vc2 = nil; } in the "ViewController 2" implementations I am able use "string1" in the title bar by doing the following.... - (void)viewDidLoad { [super viewDidLoad]; self.navigationItem.title = string1; UIBarButtonItem *addButton = [[[UIBarButtonItem alloc] initWithImage:[UIImage imageNamed:@"icon_time.png"] style:UIBarButtonItemStylePlain //style:UIBarButtonItemStyleBordered target:self action:@selector(goToThirdView)] autorelease]; self.navigationItem.rightBarButtonItem = addButton; } but I also have a NavBar Button on the right side that I would like to push a new view - (void)goToThirdView { ViewController3 *vc3 = [[ViewController3 alloc] initWithNibName:@"ViewController3" bundle:[NSBundle mainBundle]]; [self.navigationController pushViewController:NESW animated:YES]; vc3.string1 = string1 ; [vc3 release]; vc3 = nil; } How do I pass on that same string to the third view? (or fourth)

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  • Linking a template class using another template class (error LNK2001)

    - by Luís Guilherme
    I implemented the "Strategy" design pattern using an Abstract template class, and two subclasses. Goes like this: template <class T> class Neighbourhood { public: virtual void alter(std::vector<T>& array, int i1, int i2) = 0; }; and template <class T> class Swap : public Neighbourhood<T> { public: virtual void alter(std::vector<T>& array, int i1, int i2); }; There's another subclass, just like this one, and alter is implemented in the cpp file. Ok, fine! Now I declare another method, in another class (including neighbourhood header file, of course), like this: void lSearch(/*parameters*/, Neighbourhood<LotSolutionInformation> nhood); It compiles fine and cleanly. When starting to link, I get the following error: 1>SolverFV.obj : error LNK2001: unresolved external symbol "public: virtual void __thiscall lsc::Neighbourhood<class LotSolutionInformation>::alter(class std::vector<class LotSolutionInformation,class std::allocator<class LotSolutionInformation> > &,int,int)" (?alter@?$Neighbourhood@VLotSolutionInformation@@@lsc@@UAEXAAV?$vector@VLotSolutionInformation@@V?$allocator@VLotSolutionInformation@@@std@@@std@@HH@Z)

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  • Accessing the value of an input element with XPath in an XSLT

    - by asymmetric
    Hi! I'm developing a web app that has a button that triggers an XSLT transformation of the document DOM, with a stylesheet fetched via AJAX. Here's a portion of the HTML: <html> <head> <title>Static Javascript-based XMR Form Creator</title> </head> <body> <h1 id="title">Static Javascript-based XMR Form Creator</h1> <div class="opt_block" id="main_opts"> Form name <input type="text" id="form_name" /> Form cols <input type="text" id="form_cols" size="3" maxlength="3" /> </div> <button id="generate">Generate source</button> <textarea rows="20" cols="50" id="xmr_source" ></textarea> </body> Inside the stylesheet, I want to access the value attribute of the first input field, the one with id form_name. The XSLT looks like this: <xsl:template match="/html/body/div[@id = 'main_opts']" > <form> <xsl:attribute name="fname"> <xsl:value-of select="input[@id = 'form_name']/@value" /> </xsl:attribute> </form> </xsl:template> The problem is that the XPath that should do the work: <xsl:value-of select="input[@id = 'form_name']/@value" /> returns nothing. Can anyone help?

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  • 2D Histogram in R: Converting from Count to Frequency within a Column

    - by Jac
    Would appreciate help with generating a 2D histogram of frequencies, where frequencies are calculated within a column. My main issue: converting from counts to column based frequency. Here's my starting code: # expected packages library(ggplot2) library(plyr) # generate example data corresponding to expected data input x_data = sample(101:200,10000, replace = TRUE) y_data = sample(1:100,10000, replace = TRUE) my_set = data.frame(x_data,y_data) # define x and y interval cut points x_seq = seq(100,200,10) y_seq = seq(0,100,10) # label samples as belonging within x and y intervals my_set$x_interval = cut(my_set$x_data,x_seq) my_set$y_interval = cut(my_set$y_data,y_seq) # determine count for each x,y block xy_df = ddply(my_set, c("x_interval","y_interval"),"nrow") # still need to convert for use with dplyr # convert from count to frequency based on formula: freq = count/sum(count in given x interval) ################ TRYING TO FIGURE OUT ################# # plot results fig_count <- ggplot(xy_df, aes(x = x_interval, y = y_interval)) + geom_tile(aes(fill = nrow)) # count fig_freq <- ggplot(xy_df, aes(x = x_interval, y = y_interval)) + geom_tile(aes(fill = freq)) # frequency I would appreciate any help in how to calculate the frequency within a column. Thanks! jac EDIT: I think the solution will require the following steps 1) Calculate and store overall counts for each x-interval factor 2) Divide the individual bin count by its corresponding x-interval factor count to obtain frequency. Not sure how to carry this out though. .

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  • Extend DOMElement object

    - by Comma
    How could I exdend objects provided with Document Object Model? Seems that there is no way according to this [issue][2]. class Application_Model_XmlSchema extends DOMElement { const ELEMENT_NAME = 'schema'; /** * @var DOMElement */ private $_schema; /** * @param DOMDocument $document * @return void */ public function __construct(DOMDocument $document) { $this->setSchema($document->getElementsByTagName(self::ELEMENT_NAME)->item(0)); } /** * @param DOMElement $schema * @return void */ public function setSchema(DOMElement $schema){ $this->_schema = $schema; } /** * @return DOMElement */ public function getSchema(){ return $this->_schema; } /** * @param string $name * @param array $arguments * @return mixed */ public function __call($name, $arguments) { if (method_exists($this->_schema, $name)) { return call_user_func_array( array($this->_schema, $name), $arguments ); } } } $version = $this->getRequest()->getParam('version', null); $encoding = $this->getRequest()->getParam('encoding', null); $source = 'http://www.w3.org/2001/XMLSchema.xsd'; $document = new DOMDocument($version, $encoding); $document->load($source); $xmlSchema = new Application_Model_XmlSchema($document); $xmlSchema->getAttribute('version'); I got an error: Warning: DOMElement::getAttribute(): Couldn't fetch Application_Model_XmlSchema in C:\Nevermind.php on line newvermind

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  • Trying to make a plugin system in C++

    - by Pirate for Profit
    I'm making a task-based program that needs to have plugins. Tasks need to have properties which can be easily edited, I think this can be done with Qt's Meta-Object Compiler reflection capabilities (I could be wrong, but I should be able to stick this in a QtPropertyBrowser?) So here's the base: class Task : public QObject { Q_OBJECT public: explicit Task(QObject *parent = 0) : QObject(parent){} virtual void run() = 0; signals: void taskFinished(bool success = true); } Then a plugin might have this task: class PrinterTask : public Task { Q_OBJECT public: explicit PrinterTask(QObject *parent = 0) : Task(parent) {} void run() { Printer::getInstance()->Print(this->getData()); // fictional emit taskFinished(true); } inline const QString &getData() const; inline void setData(QString data); Q_PROPERTY(QString data READ getData WRITE setData) // for reflection } In a nutshell, here's what I want to do: // load plugin // find all the Tasks interface implementations in it // have user able to choose a Task and edit its specific Q_PROPERTY's // run the TASK It's important that one .dll has multiple tasks, because I want them to be associated by their module. For instance, "FileTasks.dll" could have tasks for deleting files, making files, etc. The only problem with Qt's plugin setup is I want to store X amount of Tasks in one .dll module. As far as I can tell, you can only load one interface per plugin (I could be wrong?). If so, the only possible way to do accomplish what I want is to create a FactoryInterface with string based keys which return the objects (as in Qt's Plug-And-Paint example), which is a terrible boilerplate that I would like to avoid. Anyone know a cleaner C++ plugin architecture than Qt's to do what I want? Also, am I safely assuming Qt's reflection capabilities will do what I want (i.e. able to edit an unknown dynamically loaded tasks' properties with the QtPropertyBrowser before dispatching)?

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  • Simple App Engine Sessions Implementation

    - by raz0r
    Here is a very basic class for handling sessions on App Engine: """Lightweight implementation of cookie-based sessions for Google App Engine. Classes: Session """ import os import random import Cookie from google.appengine.api import memcache _COOKIE_NAME = 'app-sid' _COOKIE_PATH = '/' _SESSION_EXPIRE_TIME = 180 * 60 class Session(object): """Cookie-based session implementation using Memcached.""" def __init__(self): self.sid = None self.key = None self.session = None cookie_str = os.environ.get('HTTP_COOKIE', '') self.cookie = Cookie.SimpleCookie() self.cookie.load(cookie_str) if self.cookie.get(_COOKIE_NAME): self.sid = self.cookie[_COOKIE_NAME].value self.key = 'session-' + self.sid self.session = memcache.get(self.key) if self.session: self._update_memcache() else: self.sid = str(random.random())[5:] + str(random.random())[5:] self.key = 'session-' + self.sid self.session = dict() memcache.add(self.key, self.session, _SESSION_EXPIRE_TIME) self.cookie[_COOKIE_NAME] = self.sid self.cookie[_COOKIE_NAME]['path'] = _COOKIE_PATH print self.cookie def __len__(self): return len(self.session) def __getitem__(self, key): if key in self.session: return self.session[key] raise KeyError(str(key)) def __setitem__(self, key, value): self.session[key] = value self._update_memcache() def __delitem__(self, key): if key in self.session: del self.session[key] self._update_memcache() return None raise KeyError(str(key)) def __contains__(self, item): try: i = self.__getitem__(item) except KeyError: return False return True def _update_memcache(self): memcache.replace(self.key, self.session, _SESSION_EXPIRE_TIME) I would like some advices on how to improve the code for better security. Note: In the production version it will also save a copy of the session in the datastore. Note': I know there are much more complete implementations available online though I would like to learn more about this subject so please don't answer the question with "use that" or "use the other" library.

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  • What is the difference between these two linq implementations?

    - by Mahesh Velaga
    I was going through Jon Skeet's Reimplemnting Linq to Objects series. In the implementation of where article, I found the following snippets, but I don't get what is the advantage that we are gettting by splitting the original method into two. Original Method: // Naive validation - broken! public static IEnumerable<TSource> Where<TSource>( this IEnumerable<TSource> source, Func<TSource, bool> predicate) { if (source == null) { throw new ArgumentNullException("source"); } if (predicate == null) { throw new ArgumentNullException("predicate"); } foreach (TSource item in source) { if (predicate(item)) { yield return item; } } } Refactored Method: public static IEnumerable<TSource> Where<TSource>( this IEnumerable<TSource> source, Func<TSource, bool> predicate) { if (source == null) { throw new ArgumentNullException("source"); } if (predicate == null) { throw new ArgumentNullException("predicate"); } return WhereImpl(source, predicate); } private static IEnumerable<TSource> WhereImpl<TSource>( this IEnumerable<TSource> source, Func<TSource, bool> predicate) { foreach (TSource item in source) { if (predicate(item)) { yield return item; } } } Jon says - Its for eager validation and then defferring for the rest of the part. But, I don't get it. Could some one please explain it in a little more detail, whats the difference between these 2 functions and why will the validations be performed in one and not in the other eagerly? Conclusion/Solution: I got confused due to my lack of understanding on which functions are determined to be iterator-generators. I assumed that, it is based on signature of a method like IEnumerable<T>. But, based on the answers, now I get it, a method is an iterator-generator if it uses yield statements.

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  • sql statement question. Need to query 3 tables in one go!

    - by Stefan
    Hey there, I have an sql database. In this database is 3 tables I need to query. The first table has all the item info called item and the other two tables has data for votes and comments called userComment and the third for votes called userItem I currently have a function which uses this sql query to get the latest more popular (in terms of both votes and comments): $sql = "SELECT itemID, COUNT(*) AS cnt FROM ( SELECT `itemID` FROM `userItem` WHERE FROM_UNIXTIME( `time` ) >= NOW() - INTERVAL 1 DAY UNION ALL SELECT `itemID` FROM `userComment` WHERE FROM_UNIXTIME( `time` ) >= NOW() - INTERVAL 1 DAY AND `itemID` > 0 ) q GROUP BY `itemID` ORDER BY cnt DESC"; I know how to change this for either by votes alone or comments.... HOWEVER - I need to query the database to only return the itemID's of the ones which have specific conditions in only the item table these are WHERE categoryID = 'xx' AND typeID = 'xx' If the sql ninja could please help me on this one? Do I have to first return the results from the above query and the for each in the array fetched then check each against the item table and see if it fits the conditions to build a new array - or is that overkill? Thanks, Stefan

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  • Avoid an "out of memory error" in Java(eclipse), when using large data structure?

    - by gnomed
    OK, so I am writing a program that unfortunately needs to use a huge data structure to complete its work, but it is failing with a "out of memory error" during its initialization. While I understand entirely what that means and why it is a problem, I am having trouble overcoming it, since my program needs to use this large structure and I don't know any other way to store it. The program first indexes a large corpus of text files that I provide. This works fine. Then it uses this index to initialize a large 2D array. This array will have nXn entries, where "n" is the number of unique words in the corpus of text. For the relatively small chunk I am testing it on(about 60 files) it needs to make approximately 30,000x30,000 entries. this will probably be bigger once I run it on my full intended corpus too. It consistently fails every time, after it indexes, while it is initializing the data structure(to be worked on later). Things I have done include: revamp my code to use a primitive "int[]" instead of a "TreeMap" eliminate redundant structures, etc... Also, I have run eclipse with "eclipse -vmargs -Xmx2g" to max out my allocated memory I am fairly confident this is not going to be a simple line of code solution, but is most likely going to require a very new approach. I am looking for what that approach is, any ideas? Thanks, B.

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  • Choosing design method for ladder-like word game.

    - by owca
    I'm trying to build a simple application, with the finished program looking like this : I will also have to implement two different GUI layouts for this. Now I'm trying to figure out the best method to perform this task. My professor told me to introduce Element class with 4 states : - empty - invisible (used in GridLayout) - first letter - other letter I've thought about following solutions (by List I mean any sort of Collection) : 1. Element is a single letter, and each line is Element[]. Game class will be array of arrays Element[]. I guess that's the dumbest way, and the validation might be troublesome. 2. Like previously but Line is a List of Element. Game is an array of Lines. 3. Like previously but Game is a List of Lines. Which one should I choose ? Or maybe do you have better ideas ? What collection would be best if to use one ?

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  • Is it possible in Perl to require a subroutine call is made?

    - by MitchelWB
    I don't know enough about Perl to even know what I'm asking for exactly, but I'm writing a series of subroutines to be available for many individual scripts that all process different incoming flat files. The process is far from perfect, but it's what I've got to deal with and I'm trying to build myself a small library of subs that make it easier for me to manage it all. Each script handles a different incoming flat file with it's own formatting, sorting, grouping and outputting requirements. One common aspect is that we have small text files that house counters that are used to name the output files so that we have no duplicate file names. Because the processing of the data is different for each file, I need to open the file to get my counter value, because this is a common operation, I'd like to put it in a sub to retrieve the counter. But then need to write specific code to process the data. And would like a second sub that allows me to update the counter with the counter once I've processed the data. Is there a way to make the second sub call a requirement if the first one is called? Ideally if it could even be an error that would prevent the script from running at all much like a syntax error. EDIT: Here is a little [ugly and simplified] psuedo-code to give a better feel for what the current process is: require "importLibrary.plx"; #open data source file open DataIn, $filename; #call getCounterInfo from importLibrary.plx to get the counter value from counter file $counter = &getCounterInfo($counterFileName); while (<DataIn>) { #Process data based on unique formatting and requirements #output to task files based on requirements and name files using the $counter #increment $counter } #update counter file with new value of $counter &updateCounterInfo($counter);

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  • RTTI Delphi Create as TValue an n-dimensional matrix.

    - by user558126
    Good day, I had tried to make recurrent function to return a TValue as a n-dimensional. matrix(2D, 3D, 4D...) for example, this procedure will show a n-dimensional matrix(it will list all elements from a n-dimensional matrix as TValue variable): Procedure Show(X:TValue); var i:integer; begin if x.IsArray then begin for i:=0 to x.GetArrayLength-1 do show(x.GetArrayElement(i)); writeln; end else write(x.ToString,' '); end; I don't understand how to create a function to create from a TValue an n-dimensional matrix. For example i need a Function CreateDynArray(Dimensions:array of integer; Kind:TTypeKind):TValue; and the function will return a TValue which is a dynamic array how contain the dimenssions for example: Return=CreateDynArray([2,3],tkInteger); will return a TValue as tkDynArray and if i will show(Return) will list 0 0 0 0 0 0 Thank you very much, and have a nice day!

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  • I need to sort php jquery gallery script alphabetically

    - by David Cahill
    know nothing about php, but I have this script that reads a folder and displays a thumbnail gallery, problem is it dosent display alphabetically. Have searched the net and seen that sort does this but have no idea where to start any help would be much appreciated. heres the script $sitename = $row_wigsites['id']; $directory = 'sites/'.$sitename.'/pans'; $allowed_types=array('jpg','jpeg','gif','png'); $file_parts=array(); $ext=''; $title=''; $i=0; $dir_handle = @opendir($directory) or die("There is an error with your image directory!"); while ($file = readdir($dir_handle)) { if($file=='.' || $file == '..') continue; $file_parts = explode('.',$file); $ext = strtolower(array_pop($file_parts)); $title = implode('.',$file_parts); $title = htmlspecialchars($title); $nomargin=''; if(in_array($ext,$allowed_types)) { if(($i+1)%4==0) $nomargin='nomargin'; echo ' <div class="pic '.$nomargin.'" style="background:url('.$directory.'/'.$file.') no-repeat 50% 50%;"> <a href="'.$directory.'/'.$file.'" title="Panoramic Stills taken at '.$title.'°" rel="pan1" target="_blank">'.$title.'</a> </div>'; $i++; } } closedir($dir_handle);

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