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• How to lazy load scripts in YUI that accompany ajax html fragments

  - by Chris Beck

  I have a web app with Tabs for Messages and Contacts (think gmail). Each Tab has a Y.on('click') event listener that retrieves an HTML fragment via Y.io() and renders the fragment via node.setContent(). However, the Contact Tab also requires contact.js to enable an Edit button in the fragment. How do I defer the cost of loading contact.js until the user clicks on the Contacts tab? How should contact.js add it's listener to the Edit button? The Complete function of my Tab's on('click') event could serialize Get.script('contact.js') after Y.io('fragment'). However, for better performance, I would prefer to download the script in parallel to downloading the HTML fragment. In that case, I would need to defer adding an event listener to the Edit button until the Edit button is available. This seems like a common RIA design pattern. What is the best way to implement this with YUI? How should I get the script? How should I defer sections of the script until elements in the fragment are available in the DOM?

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• DataReader-DataSet Hybrid solution

  - by G33kKahuna

  My solution architects and I have exhausted both pure Dataset and Datareader solutions. Basically we have a Microsoft.NET 2.0 windows service application that pulls data based on a query and processes additional tasks per record; almost a poor mans workflow system. The recordsets are broader (in terms of the columns) and deeper (in terms of number of records). We observed that DataSet performs much better in terms of performance but runs into contraints as # of records increase say 100K+ we start seeing System.OutOfMemoryException on a 4G machine with processModel configured to run at memoryLimit set to 85. Since this is a multi-threaded app, there could be multiple threads processing different queries and building different DataSets, so we run into the exception sooner in that case DataReader on the other hand works but is a lot slower and hits other contraints; if there is some sort of disconnect it has to start over again or leaves open connections on the DB side and worst case takes down the service completely etc. So, we decided the best option would be some sort of hybrid solution. I'm open to guidance and suggestions. Are there any hybrid solutions available? Any other suggestions

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• How to use HSQLDB in Oracle query syntax mode?

  - by Jan Algermissen

  I am trying to use HSQLDB as an embedded database in a spring application (for testing). As the target production database is Oracle, I would like to use HSQLDBs Oracle syntax mode feature. In the Spring config I use <jdbc:embedded-database type="HSQL" id="dataSource"> </jdbc:embedded-database> <jdbc:initialize-database data-source="dataSource" enabled="true"> <jdbc:script location="classpath:schema.sql"/> </jdbc:initialize-database> And in schema.sql at the top I wrote: SET DATABASE SQL SYNTAX ORA TRUE; However, when running my test, I get the following error: java.sql.SQLException: Unexpected token: DATABASE in statement [SET DATABASE SQL SYNTAX ORA TRUE] Is this a syntax error or a permissions error or something entirely different? Thanks - also for any pointers that might lead to the answer. Given that HSQL is the Spring default for jdbc:embedded-database and given the target is Oracle, this scenario should actually be very common. However, I found nothing on the Web even touching the issue.

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• FIFO dequeueing in python?

  - by Aaron Ramsey

  hello again everybody— I'm looking to make a functional (not necessarily optimally efficient, as I'm very new to programming) FIFO queue, and am having trouble with my dequeueing. My code looks like this: class QueueNode: def __init__(self, data): self.data = data self.next = None def __str__(self): return str(self.data) class Queue: def__init__(self): self.front = None self.rear = None self.size = 0 def enqueue(self, item) newnode = QueueNode(item) newnode.next = None if self.size == 0: self.front = self.rear = newnode else: self.rear = newnode self.rear.next = newnode.next self.size = self.size+1 def dequeue(self) dequeued = self.front.data del self.front self.size = self.size-1 if self.size == 0: self.rear = None print self.front #for testing if I do this, and dequeue an item, I get the error "AttributeError: Queue instance has no attribute 'front'." I guess my function doesn't properly assign the new front of the queue? I'm not sure how to fix it though. I don't really want to start from scratch, so if there's a tweak to my code that would work, I'd prefer that—I'm not trying to minimize runtime so much as just get a feel for classes and things of that nature. Thanks in advance for any help, you guys are the best.

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• Does this mimic perfectly a function template specialization?

  - by zeroes00

  Since the function template in the following code is a member of a class template, it can't be specialized without specializing the enclosing class. But if the compiler's full optimizations are on (assume Visual Studio 2010), will the if-else-statement in the following code get optimized out? And if it does, wouldn't it mean that for all practical purposes this IS a function template specialization without any performance cost? template<typename T> struct Holder { T data; template<int Number> void saveReciprocalOf(); }; template<typename T> template<int Number> void Holder<T>::saveReciprocalOf() { //Will this if-else-statement get completely optimized out if(Number == 0) data = (T)0; else data = (T)1 / Number; } //----------------------------------- void main() { Holder<float> holder; holder.saveReciprocalOf<2>(); cout << holder.data << endl; }

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• [Java] Nested methods vs "piped" methods, which is better?

  - by Michael Mao

  Hi: Since uni, I've programming in Java for 3 years, although I am not fully dedicated to this language, I have spent quite some time in it, nevertheless. I understand both ways, just curious which style do you prefer. public class Test{ public static void main(String[] args) { System.out.println(getAgent().getAgentName()); } private static Agent getAgent() { return new Agent(); }} class Agent{ private String getAgentName() { return "John Smith"; }} I am pretty happy with nested method calls such like the following public class Test{ public static void main(String[] args) { getAgentName(getAgent()); } private static void getAgentName(Agent agent) { System.out.println(agent.getName()); } private static Agent getAgent() { return new Agent(); }} class Agent { public String getName(){ return "John Smith"; }} They have identical output I saw "John Smith" twice. I wonder, if one way of doing this has better performance or other advantages over the other. Personally I prefer the latter, since for nested methods I can certainly tell which starts first, and which is after. The above code is but a sample, The code that I am working with now is much more complicated, a bit like a maze... So switching between the two styles often blows my head in no time.

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• Ruby on Rails script/console printing more than expected

  - by Lloyd

  I have a simple model setup in my Ruby on Rails app. (User {name, username, lat, lon}) and am writing a basic extension to the model. I would like the method to return users within a certain distance. It all works just fine in the page view, but as I am debugging I would like to work through some testing using the script/console. My question: It seems to be printing to the screen the entire result set when I run it from the command line and script/console. My model: class User < ActiveRecord::Base def distance_from(aLat, aLon) Math.sqrt((69.1*(aLat - self.lat))**2 + (49*(aLon - self.lon))**2 ) end def distance_from_user(aUser) distance_from(aUser.lat, aUser.lon) end def users_within(distance) close_users = [] users = User.find(:all) users.each do |u| close_users << u if u.distance_from_user(self) < distance end return close_users end end and from the command line I am running >> u = User.find_by_username("someuser") >> print u.users_within(1) So, I guess I would like to know why it's printing the whole result set, and if there is a way to suppress it so as to only print what I want?

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• how do i work bool!

  - by user350217

  HI! im a beginner and im really getting frustrated with this whole concept. i dont understand how to exactly use the bool function. i know what it is but i cantfigure out how to make it work in my program. Im trying to say that if my variable "selection" is any letter beween 'A' and 'I' then it is valid and can continue on to the next function which is called calcExchangeAmt(amtExchanged, selection). if it is false i want it to ask the user if they want to repeat the program and if they agree to repeat i want it to clear the screen and restart to the main function. please help edit my work! this is my bool function: bool isSelectionValid(char selection, char yesNo, double amtExchanged) { bool validData; validData = true; if((selection >= 'a' && selection <= 'i') || (selection >= 'A' && selection <= 'I')) { validData = calcExchangeAmt (amtExchanged, selection); } else(validData == false); { cout<<"Do you wish to continue? (Y for Yes / N for No)"; cin>>yesNo; } do { main(); } while ((yesNo =='y')||(yesNo == 'Y')); { system("cls"); } return 0; } this is the warning that im gettng: warning C4800: 'double' : forcing value to bool 'true' or 'false' (performance warning)

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• Email as a view.

  - by Hal

  I've been in some discussion recently about where email (notifications, etc...) should be sent in an ASP.NET MVC application. My nemesis grin argues that it only makes sense that the email should be sent from the controller. I argue that an email is simply an alternate or augmented view through a different channel. Much like I would download a file as the payload of an ActionResult, the email is simply delivered through a different protocol. I've worked an extension method that allows me to do the following: <% Html.RenderEmail(model.FromAddress, model.ToAddress, model.Subject); %> which I actually include within my the view that is displayed on the screen. The beauty is that, based on convention, if I call RenderEmail from a parent view named MyView.ascx, I attempt to render the contents of a view named MyViewEmail.ascx, unless it is not found, in which case I simply email a copy of parent view. It certainly does make it testable (I still have an ISMTPService injected for testing), I wondered if anyone had any thoughts on whether or not this breaks from good practice. In use it has been extremely handy when we needed to easily send an email or modify the contents of the emailed results vs the browser rendered results. Thanks, Hal

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• How can I get the mapi system stub dll to pass extended mapi calls to my dll?

  - by Bogatyr

  For various reasons (questioning the reasons is not helpful to me), I'd like to implement my own extended mapi dll for windows xp. I have a skeleton dll now, just a few entrypoints exist for testing, but the system mapi stub (c:\windows\system32\mapi32.dll, I've checked that it's identical to mapistub.dll) will not pass through calls to my dll, while it happily passes the same calls through to MS Outlook's msmapi32.dll, (MAPIInitialize, MAPILoginEx are two such calls). There's some secret handshake between the stub and the extended mapi dll wherein the stub checks that "yup, it's an extended mapi dll": maybe it's the presence of some additional entrypoints I haven't implemented yet, maybe it's the return value from some function, I don't know. I've tried tracing a sample app I wrote that calls MAPIInitialize with STraceNT and ProcessMonitor but that didn't show anything obvious. Tracing has shown that indeed the stub loads my dll, but then finds the secret sauce is missing apparently, and returns an error code instead of calling my dll's function. What more could be needed for calling MAPIInitialize than the presence of MAPIInitialize in my dll's exports table? GetProcAddress says it's there. What I'd like to know is how to minimally extend my skeleton extended mapi dll so that the stub mapi dll will pass through extended mapi calls to my dll. What's the secret sauce? I'd rather not spend a painful week in msvc reverse engineering the stub behavior.

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• Porting WebGL game to iPhone's native OpenGL?

  - by ArtPulse

  We are developing a web game that uses WebGL for the two biggest parts of it. Working with HTML / CSS was too slow and too limited, so it's off the table. Thing is, iOS does not support WebGL publicly just yet, only on iAd. It is my guess Apple will eventually support it once the security issues they and Microsoft claim it has are fixed, and looks stable enough. Problem is, if Apple does not do this by the release of the next mayor iOS version, then we will have in our hands a mobile WebGL game that does not run. 6 months of development and testing to waste. So, questions: If that was the case, how viable (regarding amount of time) is it porting the WebGL part of the game to native iPhone OpenGL? I'm afraid that porting will take longer than the development of the game itself. I saw posts on Stack Overflow (like this) that suggested, on Android, adding the OpenGL interface manually to a WebKit element. It'd be slower than native. But either way... Is this something that could be accepted in the AppStore? Apple is very restrictive with these kind of stuff... Thank you all for your time!

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• Error trying to use rand from std library cstdlib with g++

  - by Matt

  I was trying to use the random function in Ubuntu compiling with g++ on a larger program and for some reason rand just gave weird compile errors. For testing purposes I made the simplest program I could and it still gives errors. Program: #include <iostream> using std::cout; using std::endl; #include <cstdlib> int main() { cout << "Random number " << rand(); return 0; } Error when compiling with the terminal sudo g++ chapter_3/tester.cpp ./test ./test: In function _start': /build/buildd/eglibc-2.10.1/csu/../sysdeps/i386/elf/start.S:65: multiple definition of_start' /usr/lib/gcc/i486-linux-gnu/4.4.1/../../../../lib/crt1.o:/build/buildd/eglibc-2.10.1/csu/../sysdeps/i386/elf/start.S:65: first defined here ./test:(.rodata+0x0): multiple definition of _fp_hw' /usr/lib/gcc/i486-linux-gnu/4.4.1/../../../../lib/crt1.o:(.rodata+0x0): first defined here ./test: In function_fini': (.fini+0x0): multiple definition of _fini' /usr/lib/gcc/i486-linux-gnu/4.4.1/../../../../lib/crti.o:(.fini+0x0): first defined here ./test:(.rodata+0x4): multiple definition of_IO_stdin_used' /usr/lib/gcc/i486-linux-gnu/4.4.1/../../../../lib/crt1.o:(.rodata.cst4+0x0): first defined here ./test: In function __data_start': (.data+0x0): multiple definition ofdata_start' /usr/lib/gcc/i486-linux-gnu/4.4.1/../../../../lib/crt1.o:(.data+0x0): first defined here ./test: In function __data_start': (.data+0x4): multiple definition of__dso_handle' /usr/lib/gcc/i486-linux-gnu/4.4.1/crtbegin.o:(.data+0x0): first defined here ./test: In function main': (.text+0xb4): multiple definition ofmain' /tmp/cceF0x0p.o:tester.cpp:(.text+0x0): first defined here ./test: In function _init': (.init+0x0): multiple definition ofinit' /usr/lib/gcc/i486-linux-gnu/4.4.1/../../../../lib/crti.o:(.init+0x0): first defined here /usr/lib/gcc/i486-linux-gnu/4.4.1/crtend.o:(.dtors+0x0): multiple definition of `_DTOR_END' ./test:(.dtors+0x4): first defined here /usr/bin/ld: error in ./test(.eh_frame); no .eh_frame_hdr table will be created. collect2: ld returned 1 exit status

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• Setting up Mercurial/TortoiseHg to work with UltraCompare

  - by Tim Pietzcker

  Hi, I'm trying to get my favorite Windows diff/merge tool, UltraCompare (V7.00) to work with Mercurial/TortoiseHg. I have set up UltraCompare in my Mercurial.ini like this (only relevant bits shown): [merge-tools] UltraCompare.executable = C:\Programme\IDM Computer Solutions\UltraCompare\uc.com UltraCompare.args = $base $local $other UltraCompare.priority = 1 UltraCompare.gui = True UltraCompare.binary = True UltraCompare.checkconflicts = True UltraCompare.checkchanged = True However, the three-way-merge fails. The path names get messed up if the path to the repository that is being merged to contains a space. I have done some more testing, and I've found out (using Process Explorer) that uc.com is called with a broken command line if there is a space in the repository's path: Compare "C:\Programme\IDM Computer Solutions\UltraCompare\uc.exe" " "c:\dokume~1\tim~1.pie\lokale~1\temp\test.txt~base.akr6au" "E:\Eigene Dateien\test\test-merge\test.txt" "c:\dokume~1\tim~1.pie\lokale~1\temp\test.txt~other.b92442" and "C:\Programme\IDM Computer Solutions\UltraCompare\uc.com" "c:\dokume~1\tim~1.pie\lokale~1\temp\test.txt~base.e7vryp" "E:\test\test-merge\test.txt" "c:\dokume~1\tim~1.pie\lokale~1\temp\test.txt~other.u_qxme" There is an extraneous " after the path of the executable in the first example - not in the second (which works fine). To me, it seems as if UltraCompare is doing everything right, and that Mercurial/TortoiseHg are passing a defective command line to it. Would you say so, too? Is there a workaround? I've just updated to Mercurial 1.5/TortoiseHg 1.0, and the problem persists. Support for other merge tools (Beyond Compare and others) has been added, sadly not UltraCompare...

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• Javascript error: Object required...tough time fixing this

  - by rtnav2301

  The situation is this: a friend of mine asked me to help her with a website she's working on called www.KeepsakePartyInvitations.com. Her original designer created this code but didn't finish the project. So here I am to help save the day. Now, once a photo has been added to the party template and the mouse is placed over the image, an alternate text message appears to the right. The message informs the visitor how to reposition and resize the image, if necessary. I'm testing the procedure in the invitation to reposition the image. I follow the directions about moving the picture, but the mouse does not let go of the photo. Where ever the mouse moves, so does the image. The same thing occurs if you want to resize the image, you follow the directions but the image does not resize. I check the error message in IE 8 and it states: Message: Object required Line: 873 Char: 3 Code: 0 URI: http://www.keepsakepartyinvitations.com/Includes/JCode.js When I checked the Javascript file, the Line 873 states: tempX = e.clientX + document.body.scrollLeft If you review the javascript file, the function where the line is located is called: function getMouseXY(e). Please help me, it has been a long while since I've worked with Javascript and I'm motivated to get this fixed. Thank you!

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• What is the best way to auto-generate INSERT statements for a SQL Server table?

  - by JosephStyons

  We are writing a new application, and while testing, we will need a bunch of dummy data. I've added that data by using MS Access to dump excel files into the relevant tables. Every so often, we want to "refresh" the relevant tables, which means dropping them all, re-creating them, and running a saved MS Access append query. The first part (dropping & re-creating) is an easy sql script, but the last part makes me cringe. I want a single setup script that has a bunch of INSERTs to regenerate the dummy data. I have the data in the tables now. What is the best way to automatically generate a big list of INSERT statements from that dataset? I'm thinking of something like in TOAD (for Oracle) where you can right-click on a grid and click Save As-Insert Statements, and it will just dump a big sql script wherever you want. The only way I can think of doing it is to save the table to an excel sheet and then write an excel formula to create an INSERT for every row, which is surely not the best way. I'm using the 2008 Management Studio to connect to a SQL Server 2005 database.

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• Can the Singleton be replaced by Factory?

  - by lostiniceland

  Hello Everyone There are already quite some posts about the Singleton-Pattern around, but I would like to start another one on this topic since I would like to know if the Factory-Pattern would be the right approach to remove this "anti-pattern". In the past I used the singleton quite a lot, also did my fellow collegues since it is so easy to use. For example, the Eclipse IDE or better its workbench-model makes heavy usage of singletons as well. It was due to some posts about E4 (the next big Eclipse version) that made me start to rethink the singleton. The bottom line was that due to this singletons the dependecies in Eclipse 3.x are tightly coupled. Lets assume I want to get rid of all singletons completely and instead use factories. My thoughts were as follows: hide complexity less coupling I have control over how many instances are created (just store the reference I a private field of the factory) mock the factory for testing (with Dependency Injection) when it is behind an interface In some cases the factories can make more than one singleton obsolete (depending on business logic/component composition) Does this make sense? If not, please give good reasons for why you think so. An alternative solution is also appreciated. Thanks Marc

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• APC not working as expected?

  - by Alix Axel

  I've the following function: function Cache($key, $value = null, $ttl = 60) { if (isset($value) === true) { apc_store($key, $value, intval($ttl)); } return apc_fetch($key); } And I'm testing it using the following code: Cache('ktime', time(), 3); // Store sleep(1); var_dump(Cache('ktime') . '-' . time()); echo '<hr />'; // Should Fetch sleep(5); var_dump(Cache('ktime') . '-' . time()); echo '<hr />'; // Should NOT Fetch sleep(1); var_dump(Cache('ktime') . '-' . time()); echo '<hr />'; // Should NOT Fetch sleep(1); var_dump(Cache('ktime') . '-' . time()); echo '<hr />'; // Should NOT Fetch And this is the output: string(21) "1273966771-1273966772" string(21) "1273966771-1273966777" string(21) "1273966771-1273966778" string(21) "1273966771-1273966779" Shouldn't it look like this: string(21) "1273966771-1273966772" string(21) "-1273966777" string(21) "-1273966778" string(21) "-1273966779" I don't understand, can anyone help me figure out this strange behavior?

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• Is it safe to reuse javax.xml.ws.Service objects

  - by Noel Ang

  I have JAX-WS style web service client that was auto-generated with the NetBeans IDE. The generated proxy factory (extends javax.xml.ws.Service) delegates proxy creation to the various Service.getPort methods. The application that I am maintaining instantiates the factory and obtains a proxy each time it calls the targetted service. Creating the new proxy factory instances repeatedly has been shown to be expensive, given that the WSDL documentation supplied to the factory constructor, an HTTP URI, is re-retrieved for each instantiation. We had success in improving the performance by caching the WSDL. But this has ugly maintenance and packaging implications for us. I would like to explore the suitability of caching the proxy factory itself. Is it safe, e.g., can two different client classes, executing on the same JVM and targetting the same web service, safely use the same factory to obtain distinct proxy objects (or a shared, reentrant one)? I've been unable to find guidance from either the JAX-WS specification nor the javax.xml.ws API documentation. The factory-proxy multiplicity is unclear to me. Having Service.getPort rather than Service.createPort does not inspire confidence.

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• Populate an SSRS Report parameter(hidden) by a sproc or user defined function

  - by Nauman

  My SSRS report fetches data from my DATAWAREHOUSE. The ASP.NET application I have is connected to an OLTP database. I invoke the SSRS Report from my ASP.NET application and provide a parameter as CustomerID(this is an application key in datawarehouse) to my report. Since my report is connected to my datawarehouse, I do not query my report databased on the OLTP's CustomerID. Instead I use my datawarehouse's surrogate key (CustomerDimKey). Now, in my report, I need to find the correct surrogate key for the CustomerID parameter, which I passed from my ASP.NET application! My report already has a parameter as @CustomerDimKey(this is used across all the report sprocs). We used it for testing, but now we'll hide this as we have integrated it with the ASP.NET application. I have already added a new parameter to the report as @CustomerID(this will have the OLTP's CustomerID), which will now get a value from ASP.NET. I need to know a way to re-use the @CustomerDimKey report parameter, which should now get value from a sql statement or a sproc once the report is requested. Based on the value contained by the @CustomerID parameter.

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• What's your most controversial programming opinion?

  - by Jon Skeet

  This is definitely subjective, but I'd like to try to avoid it becoming argumentative. I think it could be an interesting question if people treat it appropriately. The idea for this question came from the comment thread from my answer to the "What are five things you hate about your favorite language?" question. I contended that classes in C# should be sealed by default - I won't put my reasoning in the question, but I might write a fuller explanation as an answer to this question. I was surprised at the heat of the discussion in the comments (25 comments currently). So, what contentious opinions do you hold? I'd rather avoid the kind of thing which ends up being pretty religious with relatively little basis (e.g. brace placing) but examples might include things like "unit testing isn't actually terribly helpful" or "public fields are okay really". The important thing (to me, anyway) is that you've got reasons behind your opinions. Please present your opinion and reasoning - I would encourage people to vote for opinions which are well-argued and interesting, whether or not you happen to agree with them.

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• Calling jquery function from ascx not working

  - by Metju

  Hi Guys, I'm having a problem with the following situation. I have an ascx which contains a submit button for a search criteria and I am trying to call a validation function in a js file I've used throughout the site (this is the first time I'm using it in an ascx). Now I've just tried this: <script type="text/javascript" src="js/jquery-1.3.2.js"></script> <script type="text/javascript" src="js/jsAdmin_Generic_SystemValidation.js"></script> <script type="text/javascript"> $(document).ready(function () { $(".submitBtn").click(function (e) { alert("test"); alert($.Validate()); alert("test 2"); }); }); </script> The file is being referenced correctly as I am already seeing posts in Firebug that are done by it. This is the function: jQuery.extend({ Validate: function () { does validation... }); Now at first I was getting "Validate() is not a function" in firebug. Since I did that alert testing, I am getting the first alert, then nothing with no errors. Can anyone shed some light? Thanks

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• URL "fragment identifier" semantics for HTML documents

  - by Pointy

  I've been working with a new installation of the "MoinMoin" wiki software. As I was playing with it, typing in mostly random test pages, I created a link with a fragment blah blah see also [[SomeStuff#whatever|some other stuff about whatever]] Then I needed to figure out how to create the anchor for that "whatever" fragment identifier. I don't recall having to do that with MediaWiki, so I had to dig around, but finally I found that MoinMoin has an "Anchor" macro: == Whatever == <<Anchor(whatever)>> Looking at the generated HTML, I was surprised to see an empty <span> tag with an "id" value of "whatever". I expected that it'd be an <a> tag with a "name" attribute of "whatever". I dug around and found the source, and there's a comment that says they changed it from an <a> tag in order to avoid some IE problem with <pre> sections. This confused me — not because of the IE thing, but because it looked to me as if their "fix" had left the whole anchor mechanism completely broken. Much to my surprise, however, further testing indicated that it worked fine. I wrote a test page with 300 <span> tags all with "id" values, and I further shocked myself when Firefox behaved exactly as I would have expected it to had I used <a> tags. It also worked when I changed all the <span> tags to <em>. So by this time, you're either as surprised as I was, or else you're thinking "how can somebody that dumb have so many reputation points?" If you're in the second category, is it really the case that I've been typing in HTML for about 15 years now — a lot of HTML — and it's somehow escaped my notice that browsers use the HTML fragment to find any sort of element with a matching "id"? mind status: blown

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• PySide Qt script doesn't launch from Spyder but works from shell

  - by Maxim Zaslavsky

  I have a weird bug in my project that uses PySide for its Qt GUI, and in response I'm trying to test with simpler code that sets up the environment. Here is the code I am testing with: http://stackoverflow.com/a/6906552/130164 When I launch that from my shell (python test.py), it works perfectly. However, when I run that script in Spyder, I get the following error: Traceback (most recent call last): File "/home/test/Desktop/test/test.py", line 31, in <module> app = QtGui.QApplication(sys.argv) RuntimeError: A QApplication instance already exists. If it helps, I also get the following warning: /usr/lib/pymodules/python2.6/matplotlib/__init__.py:835: UserWarning: This call to matplotlib.use() has no effect because the the backend has already been chosen; matplotlib.use() must be called *before* pylab, matplotlib.pyplot, or matplotlib.backends is imported for the first time. Why does that code work when launched from my shell but not from Spyder? Update: Mata answered that the problem happens because Spyder uses Qt, which makes sense. For now, I've set up execution in Spyder using the "Execute in an external system terminal" option, which doesn't cause errors but doesn't allow debugging, either. Does Spyder have any built-in workarounds to this?

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• How should I avoid memoization causing bugs in Ruby?

  - by Andrew Grimm

  Is there a consensus on how to avoid memoization causing bugs due to mutable state? In this example, a cached result had its state mutated, and therefore gave the wrong result the second time it was called. class Greeter def initialize @greeting_cache = {} end def expensive_greeting_calculation(formality) case formality when :casual then "Hi" when :formal then "Hello" end end def greeting(formality) unless @greeting_cache.has_key?(formality) @greeting_cache[formality] = expensive_greeting_calculation(formality) end @greeting_cache[formality] end end def memoization_mutator greeter = Greeter.new first_person = "Bob" # Mildly contrived in this case, # but you could encounter this in more complex scenarios puts(greeter.greeting(:casual) << " " << first_person) # => Hi Bob second_person = "Sue" puts(greeter.greeting(:casual) << " " << second_person) # => Hi Bob Sue end memoization_mutator Approaches I can see to avoid this are: greeting could return a dup or clone of @greeting_cache[formality] greeting could freeze the result of @greeting_cache[formality]. That'd cause an exception to be raised when memoization_mutator appends strings to it. Check all code that uses the result of greeting to ensure none of it does any mutating of the string. Is there a consensus on the best approach? Is the only disadvantage of doing (1) or (2) decreased performance? (I also suspect freezing an object may not work fully if it has references to other objects) Side note: this problem doesn't affect the main application of memoization: as Fixnums are immutable, calculating Fibonacci sequences doesn't have problems with mutable state. :)

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• Simplest way to automatically alter "const" value in Java during compile time

  - by Michael Mao

  Hi all: This is a question corresponds to my uni assignment so I am very sorry to say I cannot adopt any one of the following best practices in a short time -- you know -- assignment is due tomorrow :( link to Best way to alter const in Java on StackOverflow Basically the only task (I hope so) left for me is the performance tuning. I've got a bunch of predefined "const" values in my single-class agent source code like this: //static final values private static final long FT_THRESHOLD = 400; private static final long FT_THRESHOLD_MARGIN = 50; private static final long FT_SMOOTH_PRICE_IDICATOR = 20; private static final long FT_BUY_PRICE_MODIFIER = 0; private static final long FT_LAST_ROUNDS_STARTTIME = 90; private static final long FT_AMOUNT_ADJUST_MODIFIER = 5; private static final long FT_HISTORY_PIRCES_LENGTH = 10; private static final long FT_TRACK_DURATION = 5; private static final int MAX_BED_BID_NUM_PER_AUC = 12; I can definitely alter the values manually and then compile the code to give it another go around. But the execution time for a thorough "statistic analysis" usually requires over 2000 times of execution, which will typically lasts more than half an hour on my own laptop... So I hope there is a way to alter values using other ways than dig into the source code to change the "const" values there, so I can automatically distributed compiled code to other people's PC and let them run the statistic analysis instead. One other reason for a automatically value adjustment is that I can try using my own agent to defeat itself by choosing different "const" values. Although my values are derived from previous history and statistical results, they are far from the most optimized values. I hope there is a easy way so I can quickly adopt that so to have a good sleep tonight while the computer does everything for me... :) Any hints on this sort of stuff? Any suggestion is welcomed and much appreciated.

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