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• Send a "304 Not Modified" for images stored in the datastore

  - by Emilien

  I store user-uploaded images in the Google App Engine datastore as db.Blob, as proposed in the docs. I then serve those images on /images/<id>.jpg. The server always sends a 200 OK response, which means that the browser has to download the same image multiple time (== slower) and that the server has to send the same image multiple times (== more expensive). As most of those images will likely never change, I'd like to be able to send a 304 Not Modified response. I am thinking about calculating some kind of hash of the picture when the user uploads it, and then use this to know if the user already has this image (maybe send the hash as an Etag?) I have found this answer and this answer that explain the logic pretty well, but I have 2 questions: Is it possible to send an Etag in Google App Engine? Has anyone implemented such logic, and/or is there any code snippet available?

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• Haskell: What is the difference between $ (dollar) and $! (dollar exclamation point)

  - by Jelle Fresen

  Can anybody explain the difference in Haskell between the operators ($) and ($!) (dollar sign vs dollar sign exclamation point)? I haven't seen the use of $! anywhere so far, but while browsing through the Haskell reference on www.zvon.org, I noticed its existence and that it has the exact same definition as $. When trying some simple statements in a Haskell interpreter (ghci), I couldn't find any difference, nor could I find any reference to the operator in the top listed tutorials when googling for haskell tutorial. So, just out of curiosity, what is the difference, if at all?

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• declaring a 2D array of pointer objects

  - by Tyler Stennette

  I'm having a tough time figuring out how to instantiate a 2D array of pointer objects. Here is how I'm doing it: Pieces* chessBoard[9][9]; When I want to set it to an actual object pointer, I'm doing the following: chessBoard[1][1] = new Rook(p1Rook); Rook is a class that inherits attributes from the Pieces class and p1Rook is a char variable set to 'R'. This class also implements virtual functions (not pure virtual) from Pieces such as move() or getPiece() that are unique to the particular chess piece. However, when I compile my program, I get the following error: ChessBoard.cpp:69: error: expected type-specifier before ‘Rook’ ChessBoard.cpp:69: error: cannot convert ‘int*’ to ‘Pieces*’ in assignment Can someone please explain what I should change to get rid of this rather annoying persistent error? I would appreciate it.

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• tomcat 6 - Cluster / BackupManager

  - by Kevin

  Hi, I have a question regarding Clustering (session replication/failover) in tomcat 6 using BackupManager. Reason I chose BackupManager, is because it replicates the session to only one other server. I am going to run through the example below to try and explain my question. I have 6 nodes setup in a tomcat 6 cluster with BackupManager. The front end is one Apache server using mod_jk with sticky session enabled Each node has 1 session each. node1 has a session from client1 node2 has a session from client2 .. .. Now lets say node1 goes down ; assuming node2 is the backup, node2 now has two sessions (for client2 and client1) The next time client1 makes a request, what exactly happens ? Does Apache "know" that node1 is down and does it send the request directly to node2 ? =OR= does it try each of the 6 instances and find out the hard way who the backup is ?

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• 2-Version software: Best VCS approach?

  - by Tom R

  I suppose I'd better explain my situation: I'm in the process of developing some software, and I'm at the stage where I'd like to split my project into two branches which differ in features. It so happens that this application is an Android application which I will be deploying on the Market, which has the constraint that every app must have a unique package identifier (sensible, no?). My current approach has been to clone the git repo of my original project, but this causes issues with package names. I want the system to be robust enough so that a bugfix/new feature on one branch will merge into another branch, but only when I want it to. Does anyone have any suggestions?

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• jQuery remove selected option from this

  - by odavy

  Hi all, first post here, I come in peace :) I've searched but can't quite find what I'm after. I am trying to manipulate the selected option of a select box. Can someone please explain why this works: $('#some_select_box').click(function() { $('#some_select_box option:selected').remove(); }); but this doesn't: $('#some_select_box').click(function() { $('this option:selected').remove(); }); I just want to use "this" instead of spelling out the id of the select box - can someone point me in the right direction for the correct syntax? It's driving me mad because it looks like it should be really simple. And I'm sure it is to someone, but not me, cos its the end of the day and I'm brain-fried... Any pointers much appreciated. Cheers

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• How to use CCR, DSS, VPL (aka Microsoft Robotics Development Studio) outside robotics?

  - by basilmir

  How to use CCR, DSS, VPL (aka Microsoft Robotics Development Studio) outside robotics? I am looking for guidance in this field. I have tried all the examples and find the framework intriguing. Can anyone post other uses and examples, outside robotics? PS. I am looking for someone to explain some of the more complex stuff to me. I have questions regarding different implementations. If anyone is interested, i am willing to pay for a one to one talk (consulting) on the advanced topics. You can reach me via email, same name as here.

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• Issue with UITextView in an animation block

  - by collin

  I'm having an issue with a UITextView inside another UIView whose frame is manipulated in an animation block when the keyboard displays. During the animation block the UIView scales beautifully and as expected, but the UITextView jumps out of it's superview(the UIView being animated) at the start of the animation. By the end of the animation, the UITextView ends up in the right place... what gives? Can anybody explain why the UITextView is jumping out of it's container view at the start of the animation? Thanks in advance.

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• initialize a numpy array

  - by Curious2learn

  Is there way to initialize a numpy array of a shape and add to it? I will explain what I need with a list example. If I want to create a list of objects generated in a loop, I can do: a = [] for i in range(5): a.append(i) I want to do something similar with a numpy array. I know about vstack, concatenate etc. However, it seems these require two numpy arrays as inputs. What I need is: big_array # Initially empty. This is where I don't know what to specify for i in range(5): array i of shape = (2,4) created. add to big_array The big_array should have a shape (10,4). How to do this? Thanks for your help.

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• Why is this not a bug in qmail?

  - by jemfinch

  I was reading DJB's "Some thoughts on security after ten years of Qmail 1.0" and he listed this function for moving a file descriptor: int fd_move(to,from) int to; int from; { if (to == from) return 0; if (fd_copy(to,from) == -1) return -1; close(from); return 0; } It occurred to me that this code does not check the return value of close, so I read the man page for close(2), and it seems it can fail with EINTR, in which case the appropriate behavior would seem to be to call close again with the same argument. Since this code was written by someone with far more experience than I in both C and UNIX, and additionally has stood unchanged in qmail for over a decade, I assume there must be some nuance that I'm missing that makes this code correct. Can anyone explain that nuance to me?

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• flex custom events bubbling

  - by Rajeshbabu TRC

  Dear Richard Szalay, i go through your answers regarding bubbling, i want explore bubbling more. Please see my sample below <mx:Application xmlns:mx="http://www.adobe.com/2006/mxml" layout="absolute" xmlns:view="com.view.*" > } ]] In my custom event class i set bubbling=true, cancelable=true I can understand from previous answer that bubbling only affects UI components; events fired from custom classes will not bubble, even if the bubbles argument is set to true. My question is how can i prevent panelClickHandler function got fired when i click button in the "Load" (custom component)?? pleas explain bubbling with good example ( like to have with custom event classes)?

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• Why are the contents of my UITableViewCell disappearing?

  - by barfoon

  Hey everyone, I am learning about using the checkmark cell accessory and am wondering why the contents of my cell is disappearing when toggling it. Here is my code: + (void) toggleCheckmarkedCell:(UITableViewCell *)cell { if (cell.accessoryType == UITableViewCellAccessoryNone) cell.accessoryType = UITableViewCellAccessoryCheckmark; else cell.accessoryType = UITableViewCellAccessoryNone; } And here is didSelectRowAtIndexPath: UITableViewCell *cell = [tableView cellForRowAtIndexPath:indexPath]; [cell setSelectionStyle:UITableViewCellSelectionStyleNone]; [RootViewController toggleCheckmarkedCell:cell]; The checkmark is toggling on/off and is visible but the main contents of the cell disappears. Can anyone explain why this is happening? Thank you,

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• PayPal testing without using Sandbox

  - by Webbo

  I am developing a website in PHP that accepts PayPal payments. It uses the IPN from PayPal and has a custom payment template etc etc. It all works great through the Sandbox server but when it comes to showing my client, I don't want to have to tell them to login to/create a Sandbox account, create a buyer account and make a payment - he hasn't got time for that and probably won't be able to do it. Therefore, my question is - is there any simple way that I can show my client the PayPal integration in "test mode" without him using the sandbox? I realise that I can set the transaction value to 0.01 and just test on the live PayPal server but that isn't an ideal solution. Cheers! Edit: Just to better explain what I mean, this is what my client sees when he first goes to checkout; As you can see, he has to login to his Sandbox account before then purchasing the item using the buyer email that he sets up. It's just confusing and totally non user-friendly.

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• how to translate Haskell into Scalaz?

  - by TOB

  One of my high school students and I are going to try to do a port of Haskell's Parsec parser combinator library into Scala. (It has the advantage over Scala's built-in parsing library that you can pass state around fairly easily because all the parsers are monads.) The first hitch I've come across is trying to figure out how Functor works in scalaz. Can someone explain how to convert this Haskell code: data Reply s u a = Ok a !(State s u) ParseError | Error ParseError instance Functor (Reply s u) where fmap f (Ok x s e) = Ok (f x) s e fmap _ (Error e) = Error e -- XXX into Scala (using Scalaz, I assume). I got as far as sealed abstract class Reply[S, U, A] case class Ok[S, U, A](a: A, state: State[S, U], error: ParseError) extends Reply[S, U, A] case class Error[S, U, A](error: ParseError) extends Reply[S, U, A] and know that I should make Reply extend the scalaz.Functor trait, but I can't figure out how to do that. (Mostly I'm having trouble figuring out what the F[_] parameter does.) Any help appreciated! Thanks, Todd

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• Importing ctype; embedding python in C++ application

  - by Drew

  I'm trying to embed python within a C++ based programming language (CCL: The compuatational control language, not that any of you have heard of it). Thus, I don't really have a "main" function to make calls from. I have made a test .cc program with a main, and when I compile it and run it, I am able to import my own python modules and system modules for use. When I embed my code in my CCL-based program and compile it (with g++), it seems I have most functionality, but I get the import error: ImportError: /usr/lib/python2.6/lib-dynload/_ctypes.so: undefined symbol: PyType_GenericNew Can someone explain this to me and how to go about solving it? It seems like I've linked the objects correctly. Thanks.

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• how does gwt work or rather how gwt loads the code into the app.html file

  - by Pero

  i would like to know what the rootPanel (which is in the entryClass) exactly is and how gwt loads the java code into the appname.html file via rootpanel. what happens there exactly? where is the connection between the rootpanel and the html file. i could not find any side which explains this process in a detail. the only thing i know i that all the created panels are div-elements. it would be very helpfulf if somebody could explain it or send some good links to websites which are explaining this issue. thx!

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• Does mod_rewrite in subdirectories' .htaccess override higher levels?

  - by Ryan

  I'm using mod_rewrite to map my old directory structure to a new one. I have the following rule in my top-level .htaccess file, and it works: RewriteEngine On RewriteCond %{REQUEST_URI} /blog/archives/(.*) RewriteRule ^.*$ /archives/%1 [L,R=301] As you can guess, this takes http://example.com/blog/archives/00001.php and redirects it to http://example.com/archives/00001.php. But when I add these rewrite rules to the .htaccess file in the /blog directory RewriteEngine on RewriteRule atom.xml$ /atom.xml [L,R=301] the top-level redirect no longer works. If I move the rule in the /blog .htaccess file to the top-levle file both rules work. Can someone explain what is happening here?

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• Why is this HTTP request continually looping?

  - by alex

  I'm probably overlooking something really obvious here. Comments are in to help explain any library specific code. public function areCookiesEnabled() { $random = 'cx67ds'; // set cookie cookie::set('test_cookie', $random); // try and get cookie, if not set to false $testCookie = cookie::get('test_cookie', false); $cookiesAppend = '?cookies=false'; // were we able to get the cookie equal ? $cookiesEnabled = ($testCookie === $random); // if $_GET['cookies'] === false , etc try and remove $_GET portion if ($this->input->get('cookies', false) === 'false' AND $cookiesEnabled) { url::redirect(str_replace($cookiesAppend, '', url::current())); // redirect return false; } // all else fails, add a $_GET[] if ( ! $cookiesEnabled) { url::redirect(url::current().$cookiesAppend); } return $cookiesEnabled; }

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• Python nested dict comprehension with sets

  - by Jasie

  Can someone explain how to do nested dict comprehensions? >> l = [set([1, 2, 3]), set([4, 5, 6])] >> j = dict((a, i) for a in s for i, s in enumerate(l)) >> NameError: name 's' is not defined I would have liked: >> j >> {1:0, 2:0, 3:0, 4: 1, 5: 1, 6: 1} I just asked a previous question about a simpler dict comprehension where the parentheses in the generator function were reduced. How come the s in the leftmost comprehension is not recognized?

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• Code to make div appear after a certain amount of time.

  - by user307783

  Hi, I'm looking for code that makes a div appear after a certain amount of time on a site. Here's the sort of thing I'm talking about: <div class="container"> <div class="secretpopout"> This is the div I want to pop out after a couple of minutes. </div> </div> I'm relatively new to javascript and jQuery, but I'm assuming I will need to use the setTimeout or something similar. I've tried finding the answer online, but if someone could explain it in a way a designer (as opposed to a programmer) would get it, that would be great - ANY LIGHT shed on this would be greatly appreciated. Thank you.

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• Apache Commons Net FTPClient and listFiles()

  - by Vladimir

  Can anyone explain me what's wrong with the following code? I tried different hosts, FTPClientConfigs, it's properly accessible via firefox/filezilla... FTPClientConfig config = new FTPClientConfig(FTPClientConfig.SYST_L8); FTPClient client = new FTPClient(); client.configure(config); client.connect("c64.rulez.org"); client.login("anonymous", "anonymous"); client.enterRemotePassiveMode(); FTPFile[] files = client.listFiles(); Assert.assertTrue(files.length > 0);

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• How do I read the cache of Chrome and Firefox programmatically on the Mac?

  - by John Gallagher

  Background I want to access the cache of Chrome and Firefox in my Cocoa application. I need to get the HTML for pages accessed recently. Safari is a piece of cake - all this information is available in SQLite data stores, but not so in Chrome and Firefox. The Problem For Firefox, the cache is in /Library/Caches/Firefox/Profiles/xxx.default/Cache with filenames _CACHE_001_ _CACHE_002_ _CACHE_003_ and _CACHE_MAP_ For Chrome, the cache is in /Library/Caches/Google/Chrome/Default/Cache with filenames data_0 data_1 data_2 and data_3 What I've tried The only article I can find that sheds any light on what format these caches are in is here. It recommends a Cache Viewer tool, but doesn't explain how one might do this programmatically. Questions Is there any way of reconstructing this data using command line tools or the Cocoa framework? Or is it much too low level? Is there another way of getting at the HTML of recent web pages that I don't know about?

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• Recognizing file - Python

  - by Francisco Aleixo

  Ok, so the title may trick you a bit, and I'm sorry for that but didn't find a better title. This question might be a bit hard to understand so I'll try my best. I have no idea how this works or if it is even possible but what I want to do is for example create a file type (lets imagine .test (in which a random file name would be random.test)). Now before I continue, its obviously easy to do this using for example: filename = "random.test" file = open(filename, 'w') file.write("some text here") But now what I would like to know is if it is possible to write the file .test so if I set it to open with a wxPython program, it recognizes it and for example opens up a Message Dialog automatically. I'm sorry if I'm being vague and in case you don't understand, let me know so I can try my best to explain you.

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• What exactly is a Monad?

  - by WeNeedAnswers

  Can someone please explain to me what a Monad is. I think I grasp Monoids and I grasp that they basically control the input of state into a system. I just look at the text in Haskell and glaze over. A simple example in python would be great. My current understanding is that a Monoid is a procedural piece of code that needs to be read from top to bottom in sequence with the output being the input for the function. I think that I may even got that wrong, but hey I am here to learn.

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• [C#] Async threaded tcp server

  - by mark_dj

  I want to create a high performance server in C# which could take about ~10k clients. Now i started writing a TcpServer with C# and for each client-connection i open a new thread. I also use one thread to accept the connections. So far so good, works fine. The server has to deserialize AMF incoming objects do some logic ( like saving the position of a player ) and send some object back ( serializing objects ). I am not worried about the serializing/deserializing part atm. My main concern is that I will have a lot of threads with 10k clients and i've read somewhere that an OS can only hold like a few hunderd threads. Are there any sources/articles available on writing a decent async threaded server ? Are there other possibilties or will 10k threads work fine ? I've looked on google, but i couldn't find much info about design patterns or ways which explain it clearly

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