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• Django gives "I/O operation on closed file" error when reading from a saved ImageField

  - by Rob Osborne

  I have a model with two image fields, a source image and a thumbnail. When I update the new source image, save it and then try to read the source image to crop/scale it to a thumbnail I get an "I/O operation on closed file" error from PIL. If I update the source image, don't save the source image, and then try to read the source image to crop/scale, I get an "attempting to read from closed file" error from PIL. In both cases the source image is actually saved and available in later request/response loops. If I don't crop/scale in a single request/response loop but instead upload on one page and then crop/scale in another page this all works fine. This seems to be a cached buffer being reused some how, either by PIL or by the Django file storage. Any ideas on how to make an ImageField readable after saving?

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• Enumerating all combinations of lists of different types

  - by jball

  Given two IEnumberables of different types, what is the best practice (considering readability and maintainability) for iterating over both lists to perform an action on all possible combinations? My initial solution was to use nested foreach loops, iterating over the first IEnumerable, and then within that loop, iterating over the second IEnumerable and passing the value from the outer and the current loop into the target method. Eg.: enum ParamOne { First, Second, Etc } List<int> paramTwo = new List<int>() { 1, 2, 3 }; void LoopExample() { foreach (ParamOne alpha in Enum.GetValues(typeof(ParamOne))) { foreach (int beta in paramTwo) { DoSomething(alpha, beta); } } } I tried to restructure it with LINQ, but ended up with something that had no obvious advantages and seemed less intuitive. A search here shows lots of questions about nesting foreachs to iterate over child properties, but I couldn't find anything about iterating over two distinct lists.

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• Need help on how to begin learning website development

  - by Golfy

  OK for the past 10 days I have been trying to figure out where to begin learning website development a dynamic one, So far everyone told me you should start with computer science and I am like What the @#$% how am I suppose to learn computer science without going to school and get a degree but I don't want a degree I just want to learn how to devlope websites. So now I am here and confused about how to put together a website. I get HTML and CSS but still have some problems designing the site now on the other had I am having trouble trying to figure out how php and database mysql is used to put together a website. I have seen videos from lynda.com and still have no Idea after I have watched the video the basic one, one that teach you the Variables, Loops, Strings ext... ok than what happens, how do you build the website with it, that is the question I am real not understand the answer to. Any help will be appreciated.

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• Last Observation Carried Forward In a data frame?

  - by Tal Galili

  Hi all, I wish to implement a "Last Observation Carried Forward" for a data set I am working on which has missing values at the end of it. Here is a simple code to do it (question after it): LOCF <- function(x) { # Last Observation Carried Forward (for a left to right series) LOCF <- max(which(!is.na(x))) # the location of the Last Observation to Carry Forward x[LOCF:length(x)] <- x[LOCF] return(x) } # example: LOCF(c(1,2,3,4,NA,NA)) LOCF(c(1,NA,3,4,NA,NA)) Now this works great for simple vectors. But if I where to try and use it on a data frame: a <- data.frame(rep("a",4), 1:4,1:4, c(1,NA,NA,NA)) a t(apply(a, 1, LOCF)) # will make a mess It will turn my data frame into a character matrix. Can you think of a way to do LOCF on a data.frame, without turning it into a matrix? (I could use loops and such to correct the mess, but would love for a more elegant solution) Cheers, Tal

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• Convert Null Value to String - C#.NET

  - by peace

  foreach (PropertyInfo PropertyItem in this.GetType().GetProperties()) { PropertyItem.SetValue(this, objDataTable.Rows[0][PropertyItem.Name.ToString()], null); } In one of the loops i get this exceptional error: Object of type 'System.DBNull' cannot be converted to type 'System.String'. The error occurs because one of the fields in the database has no value (null), so the string property could not handle it. How can i convert this null to string? I got this solution If you know a shorter or better one, feel free to post it. I'm trying to avoid checking on every loop is current value is null or not.

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• How does functional programming work?

  - by Headcrab

  I'm used to imperative/OO programming (know C, C++, Python, PHP, etc.). I wanted to get into functional programming but there are some things unclear to me. Take for example the languages F# and Haskell: How do you implement loops? By recursion? Eew. What about conditions? How can you get by without variables? I mean.. What do we have RAM for.. storing variables, right?

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• An efficient code to determine if a set is a subset of another set

  - by Edward

  I am looking for an efficient way to determine if a set is a subset of another set in Matlab or Mathematica. Example: Set A = [1 2 3 4] Set B = [4 3] Set C = [3 4 1] Set D = [4 3 2 1] The output should be: Set A Sets B and C belong to set A because A contains all of their elements, therefore, they can be deleted (the order of elements in a set doesn't matter). Set D has the same elements as set A and since set A precedes set D, I would like to simply keep set A and delete set D. So there are two essential rules: 1. Delete a set if it is a subset of another set 2. Delete a set if its elements are the same as those of a preceding set My Matlab code is not very efficient at doing this - it mostly consists of nested loops. Suggestions are very welcome! Additional explanation: the issue is that with a large number of sets there will be a very large number of pairwise comparisons.

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• Yet another C# Deadlock Debugging Question

  - by Roo

  Hi All, I have a multi-threaded application build in C# using VS2010 Professional. It's quite a large application and we've experienced the classing GUI cross-threading and deadlock issues before, but in the past month we've noticed the appears to lock up when left idle for around 20-30 minutes. The application is irresponsive and although it will repaint itself when other windows are dragged in front of the application and over it, the GUI still appears to be locked... interstingly (unlike if the GUI thread is being used for a considerable amount of time) the Close, Maximise and minimise buttons are also irresponsive and when clicked the little (Not Responding...) text is not displayed in the title of the application i.e. Windows still seems to think it's running fine. If I break/pause the application using the debugger, and view the threads that are running. There are 3 threads of our managed code that are running, and a few other worker threads whom the source code cannot be displayed for. The 3 threads that run are: The main/GUI thread A thread that loops indefinitely A thread that loops indefinitely If I step into threads 2 and 3, they appear to be looping correctly. They do not share locks (even with the main GUI thread) and they are not using the GUI thread at all. When stepping into the main/GUI thread however, it's broken on Application.Run... This problem screams deadlock to me, but what I don't understand is if it's deadlock, why can't I see the line of code the main/GUI thread is hanging on? Any help will be greatly appreciated! Let me know if you need more information... Cheers, Roo -----------------------------------------------------SOLUTION-------------------------------------------------- Okay, so the problem is now solved. Thanks to everyone for their suggestions! Much appreciated! I've marked the answer that solved my initial problem of determining where on the main/UI thread the application hangs (I handn't turned off the "Enable Just My Code" option). The overall issue I was experiencing was indeed Deadlock, however. After obtaining the call-stack and popping the top half of it into Google I came across this which explains exactly what I was experiencing... http://timl.net/ This references a lovely guide to debugging the issue... http://www.aaronlerch.com/blog/2008/12/15/debugging-ui/ This identified a control I was constructing off the GUI thread. I did know this, however, and was marshalling calls correctly, but what I didn't realise was that behind the scenes this Control was subscribing to an event or set of events that are triggered when e.g. a Windows session is unlocked or the screensaver exits. These calls are always made on the main/UI thread and were blocking when it saw the call was made on the incorrect thread. Kim explains in more detail here... http://krgreenlee.blogspot.com/2007/09/onuserpreferencechanged-hang.html In the end I found an alternative solution which did not require this Control off the main/UI thread. That appears to have solved the problem and the application no longer hangs. I hope this helps anyone who's confronted by a similar problem. Thanks again to everyone on here who helped! (and indirectly, the delightful bloggers I've referenced above!) Roo -----------------------------------------------------SOLUTION II-------------------------------------------------- Aren't threading issues delightful...you think you've solved it, and a month down the line it pops back up again. I still believe the solution above resolved an issue that would cause simillar behaviour, but we encountered the problem again. As we spent a while debugging this, I thought I'd update this question with our (hopefully) final solution: The problem appears to have been a bug in the Infragistics components in the WinForms 2010.1 release (no hot fixes). We had been running from around the time the freeze issue appeared (but had also added a bunch of other stuff too). After upgrading to WinForms 2010.3, we've yet to reproduce the issue (deja vu). See my question here for a bit more information: 'http://stackoverflow.com/questions/4077822/net-4-0-and-the-dreaded-onuserpreferencechanged-hang'. Hans has given a nice summary of the general issue. I hope this adds a little to the suggestions/information surrounding the nutorious OnUserPreferenceChanged Hang (or whatever you'd like to call it). Cheers, Roo

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• Anchoring the Action URL of a Form

  - by John

  Hello, I am using a function that leads users to a file called "comments2.php": <form action="http://www...com/.../comments/comments2.php" method="post"> On comments2.php, data passed over from the form is inserted into MySQL: $query = sprintf("INSERT INTO comment VALUES (NULL, %d, %d, '%s', NULL)", $uid, $subid, $comment); mysql_query($query) or die(mysql_error()); Then, later in comments2.php, I am using a query that loops through entries meeting certain criteria. The loop contains a row with the following information: echo '<td rowspan="3" class="commentname1" id="comment-' . $row["commentid"] . '">'.stripslashes($row["comment"]).'</td>'; For the function above, I would like the URL to be anchored by the highest value of "commentid" for id="comment-' . $row["commentid"] . '" How can this be done? Thanks in advance, John

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• combining dynamic text with regular expressions in php

  - by pfunc

  I am experimenting with finding popular keywords using curl, php and regular expressions. I have an array of non-specific nouns that I am matching my keyword search up. So I am looking for words like "the", "and", "that" etc. and taking them out of the keyword search. so I have an array of words like so: $wordArr = [the, and, at,....]; and then running something like: && preg_match('(\bmyword\w*\b)', $key) == false how do I combine these two so it loops through the array finding out if any of the words in the array match the regular expression? I guess I could just do a for loop, but though maybe I could use in_array($wordArr, $key).. or something like that.

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• PHP - Too many mysql_query("SELECT .. ") .. ?

  - by Mike

  Hey, I'm making an e-shop and to display the tree of categories and all the products with their multiple variations of prices I made like more than 150 mysql_query("SELECT ..."); queries on one page. (If I count the "while" loops). Is it too many, and if yes, can it have any negative effect? (ofc. it takes longer to load the data ..) Also can I anyhow achieve the effect of this code without doing it that way? $result2 = mysql_query("SELECT * FROM ceny WHERE produkt_id='$id' ORDER BY gramaz"); $result3 = mysql_query("SELECT * FROM ceny WHERE produkt_id='$id' ORDER BY gramaz"); $result4 = mysql_query("SELECT * FROM ceny WHERE produkt_id='$id' ORDER BY gramaz"); $result5 = mysql_query("SELECT * FROM ceny WHERE produkt_id='$id' ORDER BY gramaz"); while( $row2 = mysql_fetch_array( $result2 )) { } while( $row3 = mysql_fetch_array( $result2 )) { } while( $row4 = mysql_fetch_array( $result2 )) { } while( $row5 = mysql_fetch_array( $result2 )) { } Thanks, Mike.

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• Is there a technical way to speed up a general program above current PC speed limit?

  - by Maksee

  Let's imagine I developed a Windows console application implementing some algorithm calculating something. Let's say it doesn't use any threads, just straightforward linear approach with ifs, loops and so on. Is there any technical way to make if run it 100x times faster than on the most advanced current PC? For example one of the way would be to run it on a super computer that emulates i386 faster than any of the existing PCs. But in this case the question what computer and does it really have ability to emulate Windows. In other words, is there real examples of such approach? Although in general it looks useless, but if there is a way, one could develop some program on his general home computer and pay for running it much faster on some other hardware. I suppose that this question could be asked on superuser.com, but since there are possible specific with such things as assembler instructions or threads, I thought that stackoverflow.com is better

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• Windows Service suddenly doing nothing

  - by TB

  Hi, My windows service is using a Thread (not a timer) which is always looping and sleeps for 1 second every loop using : evet.WaitOne(interval); When I start the service it works fine and I can see in the task manager that it is running, consuming and releasing memory, consuming processor ... etc that is all normal, but after a while (random amount of time) the service simply stops!! it is still there in the task manager but it is not consuming any processor work now and its consumption to the memory is not changing. it simply (died but still there in the task manager like a Zombie). I know that many exceptions might have happened during running the service (it is really doing many things) but all those exceptions are handled in Try catch blocks, so why is my "always looping" thread stops ??? This thread also logs every time he loops, when he is freezig in this way he is not logging anything (of course)

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• Get positions for NAs only in the "middle" of a matrix column

  - by Abiel

  I want to obtain an index that refers to the positions of NA values in a matrix where the index is true if a given cell is NA and there is at least one non-NA value before and after it in the column. For example, given the following matrix [,1] [,2] [,3] [,4] [1,] NA 1 NA 1 [2,] 1 NA NA 2 [3,] NA 2 NA 3 the only value of the index that comes back TRUE should be [2,2]. Is there a compact expression for what I want to do? If I had to I could loop through columns and use something like min(which(!is.na(x[,i]))) to find the first non-NA value in each column, and then set all values before that to FALSE (and the same for all values after the max). This way I would not select leading and trailing NA values. But this seems a bit messy, so I'm wondering if there is a cleaner expression that does this without loops.

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• Efficient synchronization of querying an array of resources

  - by Erel Segal Halevi

  There is a list of N resources, each of them can be queried by at most a single thread at a time. There are serveral threads that need to do the same thing at approximately the same time: query each of the resources (each thread has a different query), in arbitrary order, and collect the responses. If each thread loops over the resources in the same order, from 0 to N-1, then they will probably have to wait for each other, which is not efficient. I thought of letting the threads loop over the resources in a random permutation, but this seems too complex and also not so efficient, for example, for 2 resources and 2 threads, in half the cases they will choose the same order and wait for each other. Is there a simple and more efficient way to solve this?

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• PHP script for creating calendar table or jquery complete solution required

  - by finn_meister

  Ok so this is what I want to make: http://i44.tinypic.com/eiwphl.jpg red = booked green = available I have data in mysql in the format of: property_id, booked_from, booked_until . Before I start trying to create the correct loops etc to create and style the table, i thought i best ask if there are already good jquery plugins / php classes create this visual interface and uncluttered enough to allow me to add a select date range method (like Google Analytics)? I'm looking for something to create a basic calendar table on a loop, which i can then style and add jquery features. Though worth asking if there's a complete package that already does what i plan on making?!! (jquery ui's date-picker doesn't look powerful enough / easy enough to modify)

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• How should I handle searching through byte arrays in Java?

  - by Zombies

  Preliminary: I am writting my own httpclient in Java. I am trying to parse out the contents of chunked encoding. Here is my dilema: Since I am trying to parse out chunked http transfer encoding with a gzip payload there is a mix of ascii and binary. I can't just take the http resp content and convert it to a string and make use of StringUtils since the binary data can easily contain nil characters. So what I need to do is some basic things for parsing out each chunk and its chunk length (as per chunked transfer/HTTP/1.1 spec). Are there any helpful ways of searching through byte arrays of binary/part ascii data for certain patterns (like a CR LF) (instead of just a single byte) ? Or must I write the for loops for this?

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• How to I correctly add brackets to this code

  - by Mohammad

  This code removes whites paces, (fyi: it's credited to be very fast) function wSpaceTrim(s){ var start = -1, end = s.length; while (s.charCodeAt(--end) < 33 ); //here while (s.charCodeAt(++start) < 33 ); //here also return s.slice( start, end + 1 ); } The while loops don't have brackets, how would i correctly add brackets to this code? while(iMean){ like this; } Thank you so much!

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• Add HTML Id's to tags in .aspx file

  - by slandau

  So I'm writing an app that lets the user select a folder, it gets all the .aspx files in that folder, and lets the users check off which ones they want to add HTML ID's to. Then they click start, and this runs private void btnStart_Click(object sender, EventArgs e) { for (int i = 0; i < listFiles.CheckedItems.Count; i++) { } } It loops through all the selected file names. How do I open each of these .aspx files in the background, and go through them and add the id="thisItemId" attribute to each tag that's like a , , , , , etc....

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• insert into several inheritance tables with OUTPUT - sql servr 2005

  - by csetzkorn

  Hi, I have a bunch of items – for simplicity reasons – a flat table with unique names seeded via bulk insert: create table #items ( ItemName NVARCHAR(255) ) The database has this structure: create table Statements ( Id INT IDENTITY NOT NULL, Version INT not null, FurtherDetails varchar(max) null, ProposalDateTime DATETIME null, UpdateDateTime DATETIME null, ProposerFk INT null, UpdaterFk INT null, primary key (Id) ) create table Item ( StatementFk INT not null, ItemName NVARCHAR(255) null, primary key (StatementFk) ) Here Item is a child of Statement (inheritance). I would like to insert items in #items using a set based approach (avoiding triggers and loops). Can this be achieved with OUTPUT in my scenario. A ‘loop based’ approach is just too slow where I use something like this: insert into Statements (Version, FurtherDetails, ProposalDateTime, UpdateDateTime, ProposerFk, UpdaterFk) VALUES (1, null, getdate(), getdate(), @user_id, @user_id) etc. This is a start for the OUTPUT based approach – but I am not sure whether this would work in my case as ItemName is only inserted into Item: insert into Statements ( Version, FurtherDetails, ProposalDateTime, UpdateDateTime, ProposerFk, UpdaterFk ) output inserted.Id ... ??? Thanks. Best wishes, Christian

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• Ruby TCPSocket doesn't notice it when server is killed

  - by user303308

  I've this ruby code that connects to a TCP server (namely, netcat). It loops 20 times, and sends "ABCD ". If I kill netcat, it takes TWO iterations of the loop for an exception to be triggered. On the first loop after netcat is killed, no exception is triggered, and "send" reports that 5 bytes have been correctly written... Which in the end is not true, since of course the server never received them. Is there a way to work around this issue ? Right now I'm losing data : since I think it's been correctly transfered, I'm not replaying it. #!/usr/bin/env ruby require 'rubygems' require 'socket' sock = TCPSocket.new('192.168.0.10', 5443) sock.sync = true 20.times do sleep 2 begin count = sock.write("ABCD ") puts "Wrote #{count} bytes" rescue Exception => myException puts "Exception rescued : #{myException}" end end

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• Programming language for fast calculations with big integers

  - by sub

  I'm doing Project Euler problems at the moment and I can solve most of them using my own programming language which uses direct C++ integers (so they are bound to 2^32 on my machine). However, at times there are problems which require me to work with very high numbers, I can't do that with native integers. So I implemented a BigInt library in my language which unfortunately gets extremely slow at times. Is there a programming language suitable for very efficient handling of big numbers? I mean that I want to do the things I could do in other programming languages with it (variables, loops, etc.), but in a faster way. If you have got tips for workarounds of the 2^32 limit in my language/C++/other languages, please tell me too!

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• CUDA small kernel 2d convolution - how to do it

  - by paulAl

  I've been experimenting with CUDA kernels for days to perform a fast 2D convolution between a 500x500 image (but I could also vary the dimensions) and a very small 2D kernel (a laplacian 2d kernel, so it's a 3x3 kernel.. too small to take a huge advantage with all the cuda threads). I created a CPU classic implementation (two for loops, as easy as you would think) and then I started creating CUDA kernels. After a few disappointing attempts to perform a faster convolution I ended up with this code: http://www.evl.uic.edu/sjames/cs525/final.html (see the Shared Memory section), it basically lets a 16x16 threads block load all the convolution data he needs in the shared memory and then performs the convolution. Nothing, the CPU is still a lot faster. I didn't try the FFT approach because the CUDA SDK states that it is efficient with large kernel sizes. Whether or not you read everything I wrote, my question is: how can I perform a fast 2D convolution between a relatively large image and a very small kernel (3x3) with CUDA?

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• Find common nodes from two linked lists using recursion

  - by Dan

  I have to write a method that returns a linked list with all the nodes that are common to two linked lists using recursion, without loops. For example, first list is 2 - 5 - 7 - 10 second list is 2 - 4 - 8 - 10 the list that would be returned is 2 - 10 I am getting nowhere with this.. What I have been think of was to check each value of the first list with each value of the second list recursively but the second list would then be cut by one node everytime and I cannot compare the next value in the first list with the the second list. I hope this makes sense... Can anyone help?

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• direct access to vector elements similar to arrays

  - by mixm

  hi. im currently creating a tile based game, where elements of the games are placed in four different vectors (since there are multiple game objects with different properties, hence stored in different vectors). these game elements themselves contain x and y coordinates similar to how they are stored in a two dimensional array. i was wondering if there was a way to access these vector elements similar to two dimensional array access (currently i am implementing an for loop to cycle the elements while comparing its coordinates). this kinda sucks when i need to refresh my display at every game cycle (since the large number of comparisons and loops). im implementing this in java btw.

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