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  • ZooKeeper and RabbitMQ/Qpid together - overkill or a good combination?

    - by Chris Sears
    Greetings, I'm evaluating some components for a multi-data center distributed system. We're going to be using message queues (via either RabbitMQ or Qpid) so agents can make asynchronous requests to other agents without worrying about addressing, routing, load balancing or retransmission. In many cases, the agents will be interacting with components that were not designed for highly concurrent access, so locking and cross-agent coordination will be needed to avoid race conditions. Also, we'd like the system to automatically respond to agent or data center failures. With the above use cases in mind, ZooKeeper seemed like it might be a good fit. But I'm wondering if trying to use both ZK and message queuing is overkill. It seems like what Zookeeper does could be accomplished by my own cluster manager using AMQP messaging, but that would be hard to get really right. On the other hand, I've seen some examples where ZooKeeper was used to implement message queuing, but I think RabbitMQ/Qpid are a more natural fit for that. Has anyone out there used a combination like this? Thanks in advance, -Chris

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  • HMM for perspective estimation in document image, can't understand the algorithm

    - by maximus
    Hello! Here is a paper, it is about estimating the perspective of binary image containing text and some noise or non text objects. PDF document The algorithm uses the Hidden Markov Model: actually two conditions T - text B - backgrouond (i.e. noise) It is hard to understand the algorithm itself. The question is that I've read about Hidden Markov Models and I know that it uses probabilities that must be known. But in this algorithm I can't understand, if they use HMM, how do they get those probabilities (probability of changing the state from S1 to another state for example S2)? I didn't find anything about training there also in that paper. So, if somebody understands it, please tell me. Also is it possible to use HMM without knowing the state change probabilities?

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  • YUI Compressor + gzip causes Illegal Character error in jQuery

    - by lo_fye
    When I minify jquery using YUI compressor, it works fine. When I then add gzip compression (and serve this version via mod rewrite), the gzipped version throws this error: illegal character in jquery.min.js on line 1 Line 1 is: ???????M???????????s?8?0???!sz?dKr?=? This results in a "jquery is not defined" error. I am using the following rewrite rules to serve up the gzipped versions: #Check to see if browser can accept gzip files. ReWriteCond %{HTTP:accept-encoding} (gzip.*) #make sure there's no trailing .gz on the url ReWriteCond %{REQUEST_FILENAME} !^.+\.gz$ #check to see if a .gz version of the file exists. RewriteCond %{REQUEST_FILENAME}.gz -f #All conditions met so add .gz to URL filename (invisibly) RewriteRule ^(.+) $1.gz [L] I can't find any references to this happening to anyone else. Thoughts?

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  • Changing the Default View Engine's view search behavior.

    - by bradhe
    I'm working with ASP.NET MVC 2. I have a bunch of partial views that I render based on different conditions within the same controller. I'd like to not put the physical partial view files in with the controller's other views. I know that when I want a ViewResult using the View() or PartialView() methods the default view engine will search through the folder in the Views directory associated with the controller (i.e. if my controller is called Register it will look in the Register folder under Views) and also in the Shared folder. Is there any way to change this behavior, or perhaps tell it specifically where to look for the view -- heck, even give it a specific file to render? Is that possible? Perhaps even a sub-folder under the Shared folder will work...

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  • Cannot read property 'onPageChanged' of undefined

    - by user3522749
    sample extension background.js code chrome.runtime.onInstalled.addListener(function() { chrome.declarativeContent.onPageChanged.removeRules(undefined, function() { chrome.declarativeContent.onPageChanged.addRules([{ conditions: [ // When a page contains a <video> tag... new chrome.declarativeContent.PageStateMatcher({ pageUrl: { hostEquals: 'www.youtube.com'} }) ], // ... show the page action. actions: [new chrome.declarativeContent.ShowPageAction() ] }]); }); }); and I got Cannot read property 'onPageChanged' of undefined in console. No problem running the code, why is that happening?

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  • Optimization of running total calculation in SQL for multiple values per join condition

    - by Kiril
    I have the following table (test_table): date value --------------- d1 10.0 d1 20.0 d2 60.0 d2 10.0 d2 -20.0 d3 40.0 I calculate the running total as follows. I use the same query twice, because first I need to calculate the values for a specifi date, and afterwards I can calculate the running total. Otherwise, joining the two tables where date is not unique, I would get too many results from the join: SELECT t1.date, SUM(t2.value) AS total FROM (SELECT date, SUM(value) AS value FROM test_table GROUP BY date) AS t1 JOIN (SELECT date, SUM(value) AS value FROM test_table GROUP BY date) AS t2 ON t1.date >= t2.date GROUP BY t1.date ORDER BY t1.date This gives me (which is fine): date total ------------- d1 30.0 d2 80.0 d3 120.0 BUT, this query isn't very efficient, because I need to change conditions in two places, if necessary. In production, the test_table is a lot bigger ( 4 Mio. rows), and the query takes too much time to complete. Question: How can I avoid using the same query twice?

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  • When is performance gain significant enough to implement that optimization?

    - by Zwei steinen
    Hi, following the text book, I do measure performance whenever I try optimizing my code. Sometimes, however, the performance gain is rather small and I can't decisively decide whether I should implement that optimization. For example, when a fix shortens an average response time of 100ms to 90ms under some conditions, should I implement that fix? What if it shortens 200ms to 190ms? How many condition should I try before I can conclude that it will be beneficial overall? I guess it's not possible to give a straight forward answer to this, as it depends on too many things, but is there a good rule of thumb that I should follow? Are there any guideline/best-practices?

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  • hierarchical clustering on correlations in Python scipy/numpy?

    - by user248237
    How can I run hierarchical clustering on a correlation matrix in scipy/numpy? I have a matrix of 100 rows by 9 columns, and I'd like to hierarchically clustering by correlations of each entry across the 9 conditions. I'd like to use 1-pearson correlation as the distances for clustering. Assuming I have a numpy array "X" that contains the 100 x 9 matrix, how can I do this? I tried using hcluster, based on this example: Y=pdist(X, 'seuclidean') Z=linkage(Y, 'single') dendrogram(Z, color_threshold=0) however, pdist is not what I want since that's euclidean distance. Any ideas? thanks.

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  • linux thread synchronization

    - by johnnycrash
    I am new to linux and linux threads. I have spent some time googling to try to understand the differences between all the functions available for thread synchronization. I still have some questions. I have found all of these different types of synchronizations, each with a number of functions for locking, unlocking, testing the lock, etc. gcc atomic operations futexes mutexes spinlocks seqlocks rculocks conditions semaphores My current (but probably flawed) understanding is this: semaphores are process wide, involve the filesystem (virtually I assume), and are probably the slowest. Futexes might be the base locking mechanism used by mutexes, spinlocks, seqlocks, and rculocks. Futexes might be faster than the locking mechanisms that are based on them. Spinlocks dont block and thus avoid context swtiches. However they avoid the context switch at the expense of consuming all the cycles on a CPU until the lock is released (spinning). They should only should be used on multi processor systems for obvious reasons. Never sleep in a spinlock. The seq lock just tells you when you finished your work if a writer changed the data the work was based on. You have to go back and repeat the work in this case. Atomic operations are the fastest synch call, and probably are used in all the above locking mechanisms. You do not want to use atomic operations on all the fields in your shared data. You want to use a lock (mutex, futex, spin, seq, rcu) or a single atomic opertation on a lock flag when you are accessing multiple data fields. My questions go like this: Am I right so far with my assumptions? Does anyone know the cpu cycle cost of the various options? I am adding parallelism to the app so we can get better wall time response at the expense of running fewer app instances per box. Performances is the utmost consideration. I don't want to consume cpu with context switching, spinning, or lots of extra cpu cycles to read and write shared memory. I am absolutely concerned with number of cpu cycles consumed. Which (if any) of the locks prevent interruption of a thread by the scheduler or interrupt...or am I just an idiot and all synchonization mechanisms do this. What kinds of interruption are prevented? Can I block all threads or threads just on the locking thread's CPU? This question stems from my fear of interrupting a thread holding a lock for a very commonly used function. I expect that the scheduler might schedule any number of other workers who will likely run into this function and then block because it was locked. A lot of context switching would be wasted until the thread with the lock gets rescheduled and finishes. I can re-write this function to minimize lock time, but still it is so commonly called I would like to use a lock that prevents interruption...across all processors. I am writing user code...so I get software interrupts, not hardware ones...right? I should stay away from any functions (spin/seq locks) that have the word "irq" in them. Which locks are for writing kernel or driver code and which are meant for user mode? Does anyone think using an atomic operation to have multiple threads move through a linked list is nuts? I am thinking to atomicly change the current item pointer to the next item in the list. If the attempt works, then the thread can safely use the data the current item pointed to before it was moved. Other threads would now be moved along the list. futexes? Any reason to use them instead of mutexes? Is there a better way than using a condition to sleep a thread when there is no work? When using gcc atomic ops, specifically the test_and_set, can I get a performance increase by doing a non atomic test first and then using test_and_set to confirm? *I know this will be case specific, so here is the case. There is a large collection of work items, say thousands. Each work item has a flag that is initialized to 0. When a thread has exclusive access to the work item, the flag will be one. There will be lots of worker threads. Any time a thread is looking for work, they can non atomicly test for 1. If they read a 1, we know for certain that the work is unavailable. If they read a zero, they need to perform the atomic test_and_set to confirm. So if the atomic test_and_set is 500 cpu cycles because it is disabling pipelining, causes cpu's to communicate and L2 caches to flush/fill .... and a simple test is 1 cycle .... then as long as I had a better ratio of 500 to 1 when it came to stumbling upon already completed work items....this would be a win.* I hope to use mutexes or spinlocks to sparilngly protect sections of code that I want only one thread on the SYSTEM (not jsut the CPU) to access at a time. I hope to sparingly use gcc atomic ops to select work and minimize use of mutexes and spinlocks. For instance: a flag in a work item can be checked to see if a thread has worked it (0=no, 1=yes or in progress). A simple test_and_set tells the thread if it has work or needs to move on. I hope to use conditions to wake up threads when there is work. Thanks!

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  • NSZombieEnabled hides EXC_BAD_ACCESS error entirely

    - by David Liu
    So I have a subclass of a UIView that starts causing EXC_BAD_ACCESS errors when I go through a specific set of conditions (run on iPad instead of iPhone or simulator, first login only). It throws the exception when the UIView subclass gets deallocated, during the last line, where I have [super dealloc]. I heard about using NSZombieEnabled, so I tossed that on to see if I could get any more information about it, but now it hides the error completely! Does anyone know a bit more about this type of situation? I thought NSZombie would start spewing stuff into my console like before, but I'm hoping that the nonexistance of errors would tell me some sort of information as well.

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  • Rail plugin acts_as_taggable_on :through

    - by Craig
    I have two models: class Employee < ActiveRecord::Base has_many :projects end class Project < ActiveRecord::Base acts_as_taggable_on :skills, :roles end I would like to find Employees using the tags associated with their projects. The geokit-rails plugin supports a similar concept, using its ':through' relationship. Ideally, I would be able to: specify which tags (i.e. skills, roles) would be included in the conditions order the employees by the total number of projects with matching tags be able to access the matching-tag count for each employee for the purposes of building a tag cloud Any thoughts would be appreciated.

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  • Which is better? private static vs private

    - by KiD0M4N
    In this code sample: public class SuperMan { private static bool IsProper(decimal x) { return x > 31.0m && x < 45.0m; } public bool CheckStuff(string a, string b, string c) { // lots of code, some of which introduces a variable x return IsProper(x) && /* other conditions */; } } Should IsProper(..) be a 'private static' or a 'private'. Assuming: IsProper(..) doesn't need to access any instance state.

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  • Doctrine: Multiple (whereIn OR whereIn) query?

    - by Tom
    I'm having trouble crafting a fairly simple query with Doctrine... I have two arrays ($countries, $cities) and I need to check whether database record values would match any inside either. I'm looking for something like: ->whereIn('country', 'city', $countries, $cities) ... with 'country' being a WHERE IN for $countries and 'city' being a WHERE IN for $city. I could separate the two out but the needed query has lots of other conditions so that's not possible. The resulting SQL I'm after would be: SELECT ... WHERE ... AND ... AND ... AND ('country' IN (1,2,3) OR 'city' IN (7,8,9)) AND ... AND ...; One could therefore think of it also as a bracketing issue only. Anyone know if this is possible with Doctrine DQL? I've looked through the documentation but can't find any direction. Thanks

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  • help me to cheat with numericUpDown1_ValueChanged event

    - by alex
    I have a Form and numericupdown control located on it. I want that in some conditions (_condition1) user cannot be able to change a value of numericupdown control. How can I do it ? I wrote some code but it works twice (double time). class Form1 : Form { bool _condition1; int _previousValue; void numericUpDown1_ValueChanged(object sender, EventArgs e) { if(_condition1) { numericUpDown1.Value = (decimal)_previousValue; } else { _previousValue = (int)numericUpDown1.Value; } } } Control must be enable.

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  • Numeric comparison difficulty in R

    - by Matt Parker
    I'm trying to compare two numbers in R as a part of a if-statement condition: (a-b) >= 0.5 In this particular instance, a = 0.58 and b = 0.08... and yet (a-b) >= 0.5 is false. I'm aware of the dangers of using == for exact number comparisons, and this seems related: (a - b) == 0.5) is false, while all.equal((a - b), 0.5) is true. The only solution I can think of is to have two conditions: (a-b) > 0.5 | all.equal((a-b), 0.5). This works, but is that really the only solution? Should I just swear off of the = family of comparison operators forever?

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  • How to prevent Closure Compiler from renaming "true", "false" and "null"

    - by Armagan Amcalar
    Google Closure Compiler renames all "true", "false" and "null" occurences in code like; var s = true, x = null, V = false; and uses these shorthands instead; in conditions such as; if (someVariable == s) now; Google Analytics code defines it's own "s" variable; overriding the value "true"; and as you can see this causes a lot of problems. I don't want to change GA code; I just want Closure Compiler to quit renaming true etc. Externs do not work. Do you know any way to accomplish this?

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  • Sorting/Paginating/Filtering Complex Multi-AR Object Tables in Rails

    - by Matt Rogish
    I have a complex table pulled from a multi-ActiveRecord object array. This listing is a combined display of all of a particular user's "favorite" items (songs, messages, blog postings, whatever). Each of these items is a full-fledged AR object. My goal is to present the user with a simplified search, sort, and pagination interface. The user need not know that the Song has a singer, and that the Message has an author -- to the end user both entries in the table will be displayed as "User". Thus, the search box will simply be a dropdown list asking them which to search on (User name, created at, etc.). Internally, I would need to convert that to the appropriate object search, combine the results, and display. I can, separately, do pagination (mislav will_paginate), sorting, and filtering, but together I'm having some problems combining them. For example, if I paginate the combined list of items, the pagination plugin handles it just fine. It is not efficient since the pagination is happening in the app vs. the DB, but let's assume the intended use-case would indicate the vast majority of the users will have less than 30 favorited items and all other behavior, server capabilities, etc. indicates this will not be a bottleneck. However, if I wish to sort the list I cannot sort it via the pagination plugin because it relies on the assumption that the result set is derived from a single SQL query, and also that the field name is consistent throughout. Thus, I must sort the merged array via ruby, e.g. @items.sort_by{ |i| i.whatever } But, since the items do not share common names, I must first interrogate the object and then call the correct sort by. For example, if the user wishes to sort by user name, if the sorted object is a message, I sort by author but if the object is a song, I sort by singer. This is all very gross and feels quite un-ruby-like. This same problem comes into play with the filter. If the user filters on the "parent item" (the message's thread, the song's album), I must translate that to the appropriate collection object method. Also gross. This is not the exact set-up but is close enough. Note that this is a legacy app so changing it is quite difficult, although not impossible. Also, yes there is some DRY that can be done, but don't focus on the style or elegance of the following code. Style/elegance of the SOLUTION is important, however! :D models: class User < ActiveRecord::Base ... has_and_belongs_to_many :favorite_messages, :class_name => "Message" has_and_belongs_to_many :favorite_songs, :class_name => "Song" has_many :authored_messages, :class_name => "Message" has_many :sung_songs, :class_name => "Song" end class Message < ActiveRecord::Base has_and_belongs_to_many :favorite_messages belongs_to :author, :class_name => "User" belongs_to :thread end class Song < ActiveRecord::Base has_and_belongs_to_many :favorite_songs belongs_to :singer, :class_name => "User" belongs_to :album end controller: def show u = User.find 123 @items = Array.new @items << u.favorite_messages @items << u.favorite_songs # etc. etc. @items.flatten! @items = @items.sort_by{ |i| i.created_at } @items = @items.paginate :page => params[:page], :per_page => 20 end def search # Assume user is searching for username like 'Bob' u = User.find 123 @items = Array.new @items << u.favorite_messages.find( :all, :conditions => "LOWER( author ) LIKE LOWER('%bob%')" ) @items << u.favorite_songs.find( :all, :conditions => "LOWER( singer ) LIKE ... " ) # etc. etc. @items.flatten! @items = @items.sort_by{ |i| determine appropriate sorting based on user selection } @items = @items.paginate :page => params[:page], :per_page => 20 end view: #index.html.erb ... <table> <tr> <th>Title (sort ASC/DESC links)</th> <th>Created By (sort ASC/DESC links))</th> <th>Collection Title (sort ASC/DESC links)</th> <th>Created At (sort ASC/DESC links)</th> </tr> <% @items.each |item| do %> <%= render { :partial => "message", :locals => item } if item.is_a? Message %> <%= render { :partial => "song", :locals => item } if item.is_a? Song %> <%end%> ... </table> #message.html.erb # shorthand, not real ruby print out message title, author name, thread title, message created at #song.html.erb # shorthand print out song title, singer name, album title, song created at

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  • Creating database desktop application with data manipulation in Netbeans using Java Persistence

    - by Lulu
    It's my first time to use Persistence in developing a Java program because I usually connect via JDBC. I read that for large amounts of data, it is best to use persistence. I tried playing with the CRUD example of Netbeans. It's not very helpful thought because it only connects to the DB and allows addition and deletion of records. I need something that will allow me to manipulate the data like if the value from column C1 of table T1 is such, it will retrieve data from table t2. In short, I need to apply conditions before knowing what to retrieve exactly. The example in CRUD example already has a specific table to retrieve and only acts like a database manager. How is it possible to retrieve a specific item first then from this, will determine the next steps to be done. I'm also using embedded JavaDB/Derby as my database (also my first time to use because I usually use remote mysql)

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  • How can I capture multiple matches from the same Perl regex?

    - by Sho Minamimoto
    I'm trying to parse a single string and get multiple chunks of data out from the same string with the same regex conditions. I'm parsing a single HTML doc that is static (For an undisclosed reason, I can't use an HTML parser to do the job.) I have an expression that looks like: $string =~ /\<img\ssrc\="(.*)"/; and I want to get the value of $1. However, in the one string, there are many img tags like this, so I need something like an array returned (@1?) is this possible?

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  • Adding an Object to Vector loses Reference using Java?

    - by thechiman
    I have a Vector that holds a number of objects. My code uses a loop to add objects to the Vector depending on certain conditions. My question is, when I add the object to the Vector, is the original object reference added to the vector or does the Vector make a new instance of the object and adds that? For example, in the following code: private Vector numbersToCalculate; StringBuffer temp = new StringBuffer(); while(currentBuffer.length() > i) { //Some other code numbersToCalculate.add(temp); temp.setLength(0); //resets the temp StringBuffer } What I'm doing is adding the "temp" StringBuffer to the numbersToCalculate Vector. Should I be creating a new StringBuffer within the loop and adding that or will this code work? Thanks for the help! Eric

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  • Conditional relation

    - by Lowgain
    I've got a model like this: Stem -id -etc And then I have Stemrelation -stem_id -related_stem_id -active I can get the related stems with the following relations class Stem < ActiveRecord::Base has_many :stemrelations has_many :related_stems, :through => :stemrelations end class Stemrelation < ActiveRecord::Base belongs_to :stem belongs_to :related_stem, :class_name => "Stem", :foreign_key => "related_stem_id" end But now I'd only like to get the active relations. I tried adding this to the Stem model: has_many :active_related, :through => :stemrelations, :source => :related_stem, :conditions => {:active => true} but this gives me an error becasue it tries to check the active flag on the stem model instead of the stemrelation. What do I change here? Thanks!

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  • SQL Server join and wildcards

    - by Ernst
    I want to get the results of a left join between two tables, with both having a column of the same name, the column on which I join. The following query is seen as valid by the import/export wizard in SQL Server, but it always gives an error. I have some more conditions, so the size wouldn't be too much. We're using SQL Server 2000 iirc and since we're using an externally developed program to interact with the database (except for some information we can't retrieve that way), we can not simply change the column name. SELECT table1.*, table2.* FROM table1 LEFT JOIN table2 ON table1.samename = table2.samename At least, I think the column name is the problem, or am I doing something else wrong?

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  • What is the most stupid coded solution you have read/improved/witnessed?

    - by Rigo Vides
    And for stupid I mean Illogical, non-effective, complex(the bad way), ugly code style. I will start: We had a requirement there when we needed to hide certain objects given the press of a button. So this framework we were using at the time provided a way to tag objects and retrieve all the objects with a certain tag in a complete iterable collection. So I presented the most logically solution given these conditions to my partner: Me: you know, tag all the objects we needed to hide with the same tag, then call the function to get them all, iterate trough them and make them hidden. Partner: I don't know, that is hardcoding for me... Me: So what do you suggest? 20 mins later... Partner: I don't know... let's put a tag to all the objects to be hidden like this, 1, 2, 3, 4, 5, 6, 7 (and so for each object to be hidden), Then we make a for from 1 to n (where n was the number of objects to hide) and we hide them all there!

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  • What static analysis tools are available for C#?

    - by Paul Mrozowski
    What tools are there available for static analysis against C# code? I know about FxCop and StyleCop. Are there others? I've run across NStatic before but it's been in development for what seems like forever - it's looking pretty slick from what little I've seen of it, so it would be nice if it would ever see the light of day. Along these same lines (this is primarily my interest for static analysis), tools for testing code for multithreading issues (deadlocks, race conditions, etc.) also seem a bit scarce. Typemock Racer just popped up so I'll be looking at that. Anything beyond this? Real-life opinions about tools you've used are appreciated.

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  • Best Practice - Validating Input In Simple GUI Application?

    - by Alex
    I'm writing a GUI app with wxwidgets in C++ for one of my programming classes. We have to validate input and throw custom exceptions if it doesn't meet certain conditions. My question is, what is best practice when it comes to this? Should I write a seperate function that checks for errors, and have my event handler's call that function? Or should I do my error-checking in my event handlers? Or does it really matter? Thanks!

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