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• K&R Exercise 1-21 - Mental incomprehension.

  - by asdfg

  The "impossible" K&R exercise. "Write a program entab that replaces strings of blanks by the minimum number of tabs and blanks to achieve the same spacing. Use the same tab stops, say every n columns. Should n be a variable or a symbolic parameter?" The problem I'm having is, I'm unsure about how to even do this correctly. I know it's not very explanatory, but that's pretty much the problem here. Most of the examples I've seen have counted a number of blanks, and replaced those series with a tab, but this isn't what its asking, I reckon I understand what its asking, but currently feel unable to do this. Could anyone help :)

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• Determine target architecture of binary file in Linux (library or executable)

  - by Fernando Miguélez

  We have an issue related to a Java application running under a (rather old) FC3 on a Advantech POS board with a Via C3 processor. The java application has several compiled shared libs that are accessed via JNI. Via C3 processor is suppossed to be i686 compatible. Some time ago after installing Ubuntu 6.10 on a MiniItx board with the same processor I found out that the previous statement is not 100% true. The Ubuntu kernel hanged on startup due to the lack of some specific and optional instructions of the i686 set in the C3 processor. These instructions missing in C3 implementation of i686 set are used by default by GCC compiler when using i686 optimizations. The solution in this case was to go with a i386 compiled version of Ubuntu distribution. The base problem with the Java application is that the FC3 distribution was installed on the HD by cloning from an image of the HD of another PC, this time an Intel P4. Afterwards the distribution needed some hacking to have it running such as replacing some packages (such as the kernel one) with the i383 compiled version. The problem is that after working for a while the system completely hangs without a trace. I am afraid that some i686 code is left somewhere in the system and could be executed randomly at any time (for example after recovering from suspend mode or something like that). My question is: Is there any tool or way to find out at what specific architecture is an binary file (executable or library) aimed provided that "file" does not give so much information?

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• Add a listener inside or outside get method

  - by James P.

  I'm learning Swing and have composed an interface using a series of get methods to add components. Is it a good practise to add a Listener inside a get method as follows? I'd like to make things as decoupled as possible. private JButton getConnectButton() { if (connectButton == null) { connectButton = new JButton(); connectButton.setText("Connect"); connectButton.setSize(new Dimension(81, 16)); connectButton.setLocation(new Point(410, 5)); connectButton.addActionListener(new ActionListener() { public void actionPerformed(ActionEvent e) { // actionPerformed code goes here } }); } return connectButton; }

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• Fast way to manually mod a number

  - by Nikolai Mushegian

  I need to be able to calculate (a^b) % c for very large values of a and b (which individually are pushing limit and which cause overflow errors when you try to calculate a^b). For small enough numbers, using the identity (a^b)%c = (a%c)^b%c works, but if c is too large this doesn't really help. I wrote a loop to do the mod operation manually, one a at a time: private static long no_Overflow_Mod(ulong num_base, ulong num_exponent, ulong mod) { long answer = 1; for (int x = 0; x < num_exponent; x++) { answer = (answer * num_base) % mod; } return answer; } but this takes a very long time. Is there any simple and fast way to do this operation without actually having to take a to the power of b AND without using time-consuming loops? If all else fails, I can make a bool array to represent a huge data type and figure out how to do this with bitwise operators, but there has to be a better way.

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• Improve Efficiency in Array comparison in Ruby

  - by user2985025

  Hi I am working on Ruby /cucumber and have an requirement to develop a comparison module/program to compare two files. Below are the requirements The project is a migration project . Data from one application is moved to another Need to compare the data from the existing application against the new ones. Solution : I have developed a comparison engine in Ruby for the above requirement. a) Get the data, de duplicated and sorted from both the DB's b) Put the data in a text file with "||" as delimiter c) Use the key columns (number) that provides a unique record in the db to compare the two files For ex File1 has 1,2,3,4,5,6 and file2 has 1,2,3,4,5,7 and the columns 1,2,3,4,5 are key columns. I use these key columns and compare 6 and 7 which results in a fail. Issue : The major issue we are facing here is if the mismatches are more than 70% for 100,000 records or more the comparison time is large. If the mismatches are less than 40% then comparison time is ok. Diff and Diff -LCS will not work in this case because we need key columns to arrive at accurate data comparison between two applications. Is there any other method to efficiently reduce the time if the mismatches are more thatn 70% for 100,000 records or more. Thanks

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• Spaces around all hyphens in a string without double-up

  - by Dave

  I'm after a regex that puts spaces around each "-" in a string, eg. 02 jaguar-leopard, tiger-panther 08 would become 02 jaguar - leopard, tiger - panther 08 Note that if the "-" already has spaces around it, no changes are to be made, eg. 02 jaguar - leopard, tiger - panther 08 should not become 02 jaguar - leopard, tiger - panther 08 The number of hyphens are unknown in advance. Thanks for any ideas... Edit: I'm not actually using a language for this. I'm using Ant Renamer (a mass file renaming utility). There are two fields in the renamer GUI, "Expression" and "New name" to provide inputs. This is from the help file as an example: Swapping artist and title from mp3 file names: "Expression" = (.*) - (.*)\.mp3 "New name" = $2 - $1.mp3 Extract episode number and title from series video files with episode number as SnnEmm followed by title: "Expression" = Code\.Quantum\.S([0-9]{2})E([0-9]{2})\.(.*)\.FRENCH.XViD\.avi "New name" = Code Quantum - $1$2 - $3.avi

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• What's a better choice for SQL-backed number crunching - Ruby 1.9, Python 2, Python 3, or PHP 5.3?

  - by Ivan

  Crterias of 'better': fast im math and simple (little of fields, many records) db transactions, convenient to develop/read/extend, flexible, connectible. The task is to use a common web development scripting language to process and calculate long time series and multidimensional surfaces (mostly selectint/inserting sets of floats and dong maths with rhem). The choice is Ruby 1.9, Python 2, Python 3, PHP 5.3, Perl 5.12, JavaScript (node.js). All the data is to be stored in a relational database (due to its heavily multidimensional nature), all the communication with outer world is to be done by means of web services.

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• How to prevent ADO.NET from altering double values when it reads from Excel files

  - by Khnle

  I have the following rows in my Excel input file: Column1 Column2 0-5 3.040 6 2.957 7 2.876 and the following code which uses ADO.NET to read it: string fileName = "input.xls"; var connectionString = string.Format("Provider=Microsoft.Jet.OLEDB.4.0; data source={0}; Extended Properties=Excel 8.0;", fileName); var dbConnection = new OleDbConnection(connectionString); dbConnection.Open(); try { var dbCommand = new OleDbCommand("SELECT * FROM [Sheet1$]", dbConnection); var dbReader = dbCommand.ExecuteReader (); while (dbReader.Read()) { string col1 = dbReader.GetValue(0).ToString(); string col2 = dbReader.GetValue(1).ToString(); } } finally { dbConnection.Close(); } The results are very disturbing. Here's why: The values of each column in the first time through the loop: col1 is empty (blank) col2 is 3.04016411633586 Second time: col1 is 6 col2 is 2.95722928448829 Third time: col1 is 7 col2 is 2.8763272933077 The first problem happens with col1 in the first iteration. I expect 0-5. The second problem happens at every iteration with col2 where ADO.NET obviously alters the values as it reads them. How to stop this mal-behavior?

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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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• Wrong date with ruby Date.today and DateTime.now

  - by Rob

  I've installed ruby-1.8.6-p383 with RVM. System ruby is 1.9.1_p378-1 I'm getting the wrong date from Date.today and DateTime.now when using ruby 1.8.. Whereas Time.now is correct: irb(main):002:0> DateTime.now.to_s => "2126--1-10618T11:23:43+00:00" irb(main):004:0> Date.today.to_s => "2126--1-10618" irb(main):005:0> Time.now => Thu Jan 28 11:55:27 +0000 2010 All is well if I switch to ruby 1.9: irb(main):003:0> DateTime.now.to_s => "2010-01-28T11:58:51+00:00" irb(main):004:0> Date.today.to_s => "2010-01-28" irb(main):005:0> Time.now => 2010-01-28 11:59:05 +0000 Any advice on how to get DateTime to work properly in ruby 1.8 would be most appreciated!

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• How to maintain long-lived python projects w.r.t. dependencies and python versions ?

  - by Gyom

  short version: how can I get rid of the multiple-versions-of-python nightmare ? long version: over the years, I've used several versions of python, and what is worse, several extensions to python (e.g. pygame, pylab, wxPython...). Each time it was on a different setup, with different OSes, sometimes different architectures (like my old PowerPC mac). Nowadays I'm using a mac (OSX 10.6 on x86-64) and it's a dependency nightmare each time I want to revive script older than a few months. Python itself already comes in three different flavours in /usr/bin (2.5, 2.6, 3.1), but I had to install 2.4 from macports for pygame, something else (cannot remember what) forced me to install all three others from macports as well, so at the end of the day I'm the happy owner of seven (!) instances of python on my system. But that's not the problem, the problem is, none of them has the right (i.e. same set of) libraries installed, some of them are 32bits, some 64bits, and now I'm pretty much lost. For example right now I'm trying to run a three-year-old script (not written by me) which used to use matplotlib/numpy to draw a real-time plot within a rectangle of a wxwidgets window. But I'm failing miserably: py26-wxpython from macports won't install, stock python has wxwidgets included but also has some conflict between 32 bits and 64 bits, and it doesn't have numpy... what a mess ! Obviously, I'm doing things the wrong way. How do you usally cope with all that chaos ?

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• Is there a FAST way to export and install an app on my phone, while signing it with my own keystore?

  - by Alexei Andreev

  So, I've downloaded my own application from the market and installed it on my phone. Now, I am trying to install a temporary new version from Eclipse, but here is the message I get: Re-installation failed due to different application signatures. You must perform a full uninstall of the application. WARNING: This will remove the application data! Please execute 'adb uninstall com.applicationName' in a shell. Launch canceled! Now, I really really don't want to uninstall the application, because I will lose all my data. One solution I found is to Export my application, creating new .apk, and then install it via HTC Sync (probably a different program based on what phone you have). The problem is this takes a long time to do, since I need to enter the password for the keystore each time and then wait for HTC Sync. It's a pain in the ass! So the question is: Is there a way to make Eclipse automatically use my keystore to sign the application (quickly and automatically)? Or perhaps to replace debug keystore with my own? Or perhaps just tell it to remember the password, so I don't have to enter it every time...? Or some other way to solve this problem?

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• Programmatically configure MATLAB

  - by Richie Cotton

  Since MathWorks release a new version of MATLAB every six months, it's a bit of hassle having to set up the latest version each time. What I'd like is an automatic way of configuring MATLAB, to save wasting time on administrative hassle. The sorts of things I usually do when I get a new version are: Add commonly used directories to the path. Create some toolbar shortcuts. Change some GUI preferences. The first task is easy to accomplish programmatically with addpath and savepath. The next two are not so simple. Details of shortcuts are stored in the file 'shortcuts.xml' in the folder given by prefdir. My best idea so far is to use one of the XML toolboxes in the MATLAB Central File Exchange to read in this file, add some shortcut details and write them back to file. This seems like quite a lot of effort, and that usually means I've missed an existing utility function. Is there an easier way of (programmatically) adding shortcuts? Changing the GUI preferences seems even trickier. preferences just opens the GUI preference editor (equivalent to File - Preferences); setpref doesn't seems to cover GUI options. The GUI preferences are stored in matlab.prf (again in prefdir); this time in traditional name=value config style. I could try overwriting values in this directly, but it isn't always clear what each line does, or how much the names differ between releases, or how broken MATLAB will be if this file contains dodgy values. I realise that this is a long shot, but are the contents of matlab.prf documented anywhere? Or is there a better way of configuring the GUI? For extra credit, how do you set up your copy of MATLAB? Are there any other tweaks I've missed, that it is possible to alter via a script?

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• Java Application/Thread Server

  - by Manrico Corazzi

  I am looking for something very close to an application server with these features: it should handle a series of threads/daemons, allowing the user to start-stop-reload each one without affecting the others it should keep libraries separated between different threads/daemons it should allow to share some libraries Currently we have some legacy code reinventing the wheel... and not a perflectly round-shaped one at that! I thought to use Tomcat, but I don't need a web server, except maybe for the simple backoffice user interface (/manager/html). Any suggestion? Is there a non-web application server, or is there a better alternative to Tomcat (more lightweight, for example, or easier to configure)? Thanks in advance.

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• How can I help fellow students struggling in programming classes?

  - by David Barry

  I'm a computer science student finishing up my second semester of programming classes. I've enjoyed them quite a bit, and learned a lot, but it seems other students are struggling with the concepts and assignments more than I am. When an assignment is due, the inevitable group email comes out the day or two before with people needing some help either with a specific part of the problem, or sometimes people just seem to have a hard time knowing where to start. I'd really like to be able to help out, but I have a hard time thinking of the right way to give them help without giving them the answer. When I'm having trouble understanding a concept, a code snippet can go along way to helping me, but at the same time if it makes a lot of sense, it can be difficult to think of another way to go about it. Plus the Academic Integrity section of each assignment is always looming overhead warning against sharing code with others. I've tried using pseudo code to help give others an idea on program flow, leaving them to figure out how to implement certain aspects of it, but I didn't get too much feedback and don't know how much it actually helped them out, or if it just confused them further. So I'm basically looking to see if anyone has experience with this, or good ways that I can help out other students to nudge them in the right direction or help them think about the problem in the right way.

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• Classical task-scheduling assignment

  - by Bruno

  I am working on a flight scheduling app (disclaimer: it's for a college project, so no code answers, please). Please read this question w/ a quantum of attention before answering as it has a lot of peculiarities :( First, some terminology issues: You have planes and flights, and you have to pair them up. For simplicity's sake, we'll assume that a plane is free as soon as the flight using it prior lands. Flights are seen as tasks: They have a duration They have dependencies They have an expected date/time for beginning Planes can be seen as resources to be used by tasks (or flights, in our terminology). Flights have a specific type of plane needed. e.g. flight 200 needs a plane of type B. Planes obviously are of one and only one specific type, e.g., Plane Airforce One is of type C. A "project" is the set of all the flights by an airline in a given time period. The functionality required is: Finding the shortest possible duration for a said project The earliest and latest possible start for a task (flight) The critical tasks, with basis on provided data, complete with identifiers of preceding tasks. Automatically pair up flights and planes, so as to get all flights paired up with a plane. (Note: the duration of flights is fixed) Get a Gantt diagram with the projects scheduling, in which all flights begin as early as possible, showing all previously referred data graphically (dependencies, time info, etc.) So the questions is: How in the world do I achieve this? Particularly: We are required to use a graph. What do the graph's edges and nodes respectively symbolise? Are we required to discard tasks to achieve the critical tasks set? If you could also recommend some algorithms for us to look up, that'd be great.

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• CUDA driver installation on a laptop with nVidia NVS140M card

  - by stanigator

  I'm trying to first figure out if my computer contains a CUDA-enabled card. It has an nVidia NVS 140M card, but I can't seem to figure out if it is the 128 MB version or 256 MB version. On the laptop purchase receipt, I found out that I ordered the 128 MB version, but the control panel description of the card said otherwise as shown below: When I ran the CUDA driver from nVidia's site, it cannot find a hardware compatible with CUDA (even though the product series is CUDA-enabled, the card does not have 256 MB minimum of memory to do so). What would be your recommendations in this case with trying to use CUDA on this computer (I'm not sure if nothing can be done at this point)? Thanks in advance.

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• Searching algorithmics: Parsing and processing a request

  - by James P.

  Say you were to create a search engine that can accept a query statement under the form of a String. The statement can be used to retrieve different types of objects with a given set of characteristics and possibly linked to other objects. In plain english or pseudo-code using an OOP approach, how would you go about parsing and processing statements as follows to get the series of desired objects ? get fruit with colour green get variety of apples, pears from Andy get strawberry with colour "deep red" and origin not Spain get total of sales of melons between 2010-10-10 and 2010-12-30 get last deliverydate of bananas from "Pete" and state not sold Hope the question is clear. If not I'll be more than happy to reformulate. P.S: This isn't homework ;)

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• Broadcast live video from web-cam via plug-in

  - by Freebrainz

  Hello guys! Could you please suggest me what kind of software should I use to broadcast live video from webcam? Web-cam is connected via USB to my server. I want to broadcast video from my webcam on my web-page (HTML, ASP.NET - doesn't matter). I don't want to develop video broadcasting from the beginning - it takes a lot of time to implement good system. I'm looking for ready-to-use plug-in/widget for my site. I found ustream.tv, but live video start playing with delay about 2 seconds... You know, it's not real-time. I need something like Skype/icq/ooVoo... plug-in/widget for my web-site. Are these plug-ins exists in internet? P.S. I know that VideoLAN has ActiveX control. Does VLC provide me with real-time video broadcasting from webcam without any delays like Skype? Thank you!

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• Learning about version control systems, Git, SVN

  - by anijhaw

  I am a basic SVN user now trying to learn GIT for a new position. I am trying the usual reading docs and watching videos. However after doing all that I still feel that there is a lot that I do not know. I was wondering if there is a place like project Euler for programming languages, that provides a series of exercises that you can do just to increase your confidence and test your knowledge about a version control system. Something thats generic enough and gets you up to speed with how to do basic things. This could also serve as a comparison point of sorts between multiple VCSs, that would show what things are easy in which VCS. If there is nothing I was planning to document my journey in learning GIT and the create an exercise of this sort.

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• Static Variables somehow maintaining state?

  - by gfoley

  I am working on an existing project, setup by another coder. I'm having some trouble understanding how state is being maintained between pages. There is a Class library which has some helper objects. Mostly these objects are just used for there static methods and rarely instantiated or inherited. This is an example class I'm testing with. public sealed class Application { public static string Test; } Now when i run something like the following in the base class of my page, I would expect the result to be "1: 2:Test" all the time (note that "1" is empty), but strangly its only this way the first time it is run. Then every time afterwards its "1:Test 2:Test". Somehow its maintaining the state of the static variable between pages and being refreshed?? Response.Write("1:" + SharedLibrary.Application.Test); SharedLibrary.Application.Test = "Test"; Response.Write(" 2:" + SharedLibrary.Application.Test); I need to create more classes like this, but want to understand why this is occurring in the first place. Many Thanks

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• Communication between lexer and parser

  - by FredOverflow

  Every time I write a simple lexer and parser, I stumble upon the same question: how should the lexer and the parser communicate? I see four different approaches: The lexer eagerly converts the entire input string into a vector of tokens. Once this is done, the vector is fed to the parser which converts it into a tree. This is by far the simplest solution to implement, but since all tokens are stored in memory, it wastes a lot of space. Each time the lexer finds a token, it invokes a function on the parser, passing the current token. In my experience, this only works if the parser can naturally be implemented as a state machine like LALR parsers. By contrast, I don't think it would work at all for recursive descent parsers. Each time the parser needs a token, it asks the lexer for the next one. This is very easy to implement in C# due to the yield keyword, but quite hard in C++ which doesn't have it. The lexer and parser communicate through an asynchronous queue. This is commonly known under the title "producer/consumer", and it should simplify the communication between the lexer and the parser a lot. Does it also outperform the other solutions on multicores? Or is lexing too trivial? Is my analysis sound? Are there other approaches I haven't thought of? What is used in real-world compilers? It would be really cool if compiler writers like Eric Lippert could shed some light on this issue.

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• Reorganizing development environment for single developer/small shop

  - by Matthew

  I have been developing for my company for approximately three years. We serve up a web portal using Microsoft .NET and MS SQL Server on DotNetNuke. I am going to leave my job full time at the end of April. I am leaving on good terms, and I really care about this company and the state of the web project. Because I haven't worked in a team environment in a long time, I have probably lost touch with what 'real' setups look like. When I leave, I predict the company will either find another developer to take over, or at least have developers work on a contractual basis. Because I have not worked with other developers, I am very concerned with leaving the company (and the developer they hire) with a jumbled mess. I'd like to believe I am a good developer and everything makes sense, but I have no way to tell. My question, is how do I set up the development environment, so the company and the next developer will have little trouble getting started? What would you as a developer like in place before working on a project you've never worked on? Here's some relevant information: There is a development server onsite and a production server offsite in a data center . There is a server where backups and source code (Sourcegear Vault) are stored. There is no formal documentation but there are comments in the code. The company budget is tight so free suggestions will help the best. I will be around after the end of April on a consulting basis so I can ask simple questions but I will not be available full time to train someone

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• Reference book on Ruby on Rails social network site for novices

  - by Christopher

  Hey, so I am a novice programmer who has only worked with HTML, CSS, and a touch of Java a couple of years ago. I am looking to try to get a social network site up and running on Ruby on Rails and was looking at RailsSpace: Building a Social Networking Website with Ruby on Rails (Addison-Wesley Professional Ruby Series) - Paperback (July 30, 2007) by Michael Hartl. This was published in 2007, however, and the newer reviews say it is not very helpful. Does anyone know if there are any new publications out there that walk you through building a social network site while teaching you the code(rather than just using a out of the box program)? Thanks

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• Is there are standard way to store a database schema outside a python app

  - by acrosman

  I am working on a small database application in Python (currently targeting 2.5 and 2.6) using sqlite3. It would be helpful to be able to provide a series of functions that could setup the database and validate that it matches the current schema. Before I reinvent the wheel, I thought I'd look around for libraries that would provide something similar. I'd love to have something akin to RoR's migrations. xml2ddl doesn't appear to be meant as a library (although it could be used that way), and more importantly doesn't support sqlite3. I'm also worried about the need to move to Python 3 one day given the lack of recent attention to xml2ddl. Are there other tools around that people are using to handle this?

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