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  • Restrictive routing best practices for Google App Engine with python?

    - by Aleksandr Makov
    Say I have a simple structure: app = webapp2.WSGIApplication([ (r'/', 'pages.login'), (r'/profile', 'pages.profile'), (r'/dashboard', 'pages.dash'), ], debug=True) Basically all pages require authentication except for the login. If visitor tries to reach a restrictive page and he isn't authorized (or lacks privileges) then he gets redirected to the login view. The question is about the routing design. Should I check the auth and ACL privs in each of the modules (pages.profile and pages.dash from example above), or just pass all requests through the single routing mechanism: app = webapp2.WSGIApplication([ (r'/', 'pages.login'), (r'/.+', 'router') ], debug=True) I'm still quite new to the GAE, but my app requires authentication as well as ACL. I'm aware that there's login directive on the server config level, but I don't know how it works and how I can tight it with my ACL logic and what's worse I cannot estimate time needed to get it running. Besides, it looks only to provide only 2 user groups: admin and user. In any case, that's the configuration I use: handlers: - url: /favicon.ico static_files: static/favicon.ico upload: static/favicon.ico - url: /static/* static_dir: static - url: .* script: main.app secure: always Or I miss something here and ACL can be set in the config file? Thanks.

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  • Using automated bdd-gui-tests to keep user-documentation-screenshots up do date?

    - by k3b
    Are there developpers out there, who (ab)use the CaptureScreenshot() function of their automated gui-tests to also create uptodate-screenshots for the userdocumentation? Background: Whithin the lifetime of an application, its gui-elements are constantly changing. It makes a lot of work to keep the userdocumentation uptodate, especially if the example data in the pictures should match the textual description. If you already have automated bdd-gui-tests why not let them take screenshots at certain points? I am currently playing with webapps in dotnet+specflow+selenium, but this topic also applies to other bdd-engines (JRuby-Cucumber, mspec, rspec, ...) and gui-test-Frameworks (WaitN, WaitR, MsWhite, ....) Any experience, thoughts or url-links to this topic would be helpfull. How is the cost/benefit relation? Is it worth the efford? What are the Drawbacks? See also: Is it practical to retroactively write specifications documenting a system via automated acceptance tests?

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  • Linear Search in Python? [closed]

    - by POTUS
    def find_interval(mesh,x): '''This function finds the interval containing x according to the following rules, mesh is an ordered list with n numbers return 0 if x < mesh[0] return n if mesh[n-1] < x return k if mesh[k-1] <= x < mesh[k] return n-1 if mesh[n-2] <= x <= mesh[n-1] This function does a Linear search. 08/29/2012 ''' for n in range(len(mesh)): for k in range(len(mesh)): if x == mesh[n]: print "Found x at index:" return n elif x<mesh[n]: return 0 elif mesh[n-1]<x: return n elif mesh[n-2]<=x<=mesh[n-1]: return n-1 elif mesh[k-1]<=x<mesh[k]: return k mesh = [0, 0.1, 0.25, 0.5, 0.6, 0.75, 0.9, 1] print mesh print find_interval(mesh, -1) print find_interval(mesh, 0) print find_interval(mesh, 0.1) print find_interval(mesh, 0.8) print find_interval(mesh, 0.9) print find_interval(mesh, 1) print find_interval(mesh, 1.01) Output: [0, 0.100000000000000, 0.250000000000000, 0.500000000000000, 0.600000000000000, 0.750000000000000, 0.900000000000000, 1] 0 Found x at index: 0 2 6 -1 -1 0 I don't think the output is correct. Can anyone help me fix it? Thanks.

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  • What does the English word "for" exactly mean in "for" loops?

    - by kol
    English is not my first language, but since the keywords in programming languages are English words, I usually find it easy to read source code as English sentences: if (x > 10) f(); = "If variable x is greater than 10, then call function f." while (i < 10) ++i; = "While variable i is less than 10, increase i by 1." But how a for loop is supposed to be read? for (i = 0; i < 10; ++i) f(i); = ??? I mean, I know what a for loop is and how it works. My problem is only that I don't know what the English word "for" exactly means in for loops.

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  • using a wiki for requirements

    - by apollodude217
    Hi, I'm looking into ways of improving requirements management. Currently, we have a Word document published on a Web site. Unfortunately, we cannot (to my knowledge) look at changes from one revision to the next. I would greatly prefer to be able to do so, much like with a wiki or VCS (or both, like the wiki's on bitbucket!). Also, each document describes changes devs are expected to meet by a given deadline. There is no collection of accumulated app features documented anywhere, so it's sometimes hard to distinguish between a bug and a (poorly-designed) feature when trying to make quick fixes to legacy apps. So I had an idea I wanted to get feedback on. What about: Using a wiki so that we can track who changed what when (mostly to even see if any edits were made since the last time one looked). Having one, say, wiki page per product rather than one per deadline, keeping up with all features of the product rather than the changes that should be implemented. This way, I can look at a particular revision of the page to see what the app should do at a given point in time, and I can look at changes to the page since the last release for the requirements to be implemented by the next deadline. Waddayathink?

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  • Convincing my coworkers to use Hudson CI

    - by in0de
    Im really aware of some benefits of using Hudson as CI server. But, im facing the problem to convince my coworkers to install and use it. To put some context, we are developing two different products (one is an enterprise search engine based on Apache Solr) and several enterprise search projects. We are facing a lot of versioning issues and i think Hudson will solve this problems. They argued about its productivity and learning curve What Hudson's benefits would you spotlight?

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  • I'm porting my app from iOS to Android: what do I need to know?

    - by kubi
    What pitfalls should I avoid? What Java language paradigms do Objective-C developers consistently misunderstand? I learned to program in Java, but I have worked in nothing but Objective-C for years now. How are the design patterns different between Android and iOS? If you've made the transition yourself, what parts of Android confused you or took you longer to learn than it should have? Is Eclipse the best OS X IDE for Android? For the record, my app is very strongly tied to UIKit and Foundation, so the word "porting" may be a misnomer; I'll actually be completely rewriting it for Android. No code reuse. Also, I'm doing this to learn Android, so I'd rather fail at the port and learn Android than take a shortcut.

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  • SOA, Java EE and data organization

    - by jolasveinn
    At the company I work for, we're currently splitting up our monolith solution into a number of small services (SOA). Many of the services are small, so we'd like to deploy a number of these services on the same application server, JBoss 7.1 in this case. As per the SOA philosophy, the independence of each service and the teams working on them is very important. What would be the best way to organize the data? Use one schema per service Would you use one datasource per schema in the application server? Or use one datasource, prefixing all DB object names with the schema name in some transparent manner? Use a shared schema, but evading any naming collisions by requiring each service to use a distinct prefix for all DB objects Other options? Am I maybe thinking this completely wrong here? :)

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  • android app unable to connect to the hsqldb server

    - by Chinta
    I am trying to connect my android app to the hsql db server. Server runs on computer-1. I can connect to the db server from local machine through java as well as Db-visualizer. I can connect to the db server from another computer(computer-2) using Db-visualizer with comouter-1 ip address. Now trying to connect from my app in Nexus 7 the same way I was connecting from computer-2. I am getting "No Suitable Driver" error. Below is the log. 11-02 12:01:41.235: W/System.err(9803): connection string <jdbc:hsqldb:hsql://192.168.2.6:9001/qBank> 11-02 12:01:41.235: W/System.err(9803): user id string <SA> 11-02 12:01:41.235: W/System.err(9803): password string <> 11-02 12:01:41.235: W/System.err(9803): ERROR: failed to get connection. 11-02 12:01:41.235: W/System.err(9803): java.sql.SQLException: No suitable driver 11-02 12:01:41.235: W/System.err(9803): at java.sql.DriverManager.getConnection(DriverManager.java:186) 11-02 12:01:41.235: W/System.err(9803): at java.sql.DriverManager.getConnection(DriverManager.java:213) 11-02 12:01:41.235: W/System.err(9803): at com.scan.util.GatherData.getConnection(GatherData.java:135)

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  • How to do dependency Injection and conditional object creation based on type?

    - by Pradeep
    I have a service endpoint initialized using DI. It is of the following style. This end point is used across the app. public class CustomerService : ICustomerService { private IValidationService ValidationService { get; set; } private ICustomerRepository Repository { get; set; } public CustomerService(IValidationService validationService,ICustomerRepository repository) { ValidationService = validationService; Repository = repository; } public void Save(CustomerDTO customer) { if (ValidationService.Valid(customer)) Repository.Save(customer); } Now, With the changing requirements, there are going to be different types of customers (Legacy/Regular). The requirement is based on the type of the customer I have to validate and persist the customer in a different way (e.g. if Legacy customer persist to LegacyRepository). The wrong way to do this will be to break DI and do somthing like public void Save(CustomerDTO customer) { if(customer.Type == CustomerTypes.Legacy) { if (LegacyValidationService.Valid(customer)) LegacyRepository.Save(customer); } else { if (ValidationService.Valid(customer)) Repository.Save(customer); } } My options to me seems like DI all possible IValidationService and ICustomerRepository and switch based on type, which seems wrong. The other is to change the service signature to Save(IValidationService validation, ICustomerRepository repository, CustomerDTO customer) which is an invasive change. Break DI. Use the Strategy pattern approach for each type and do something like: validation= CustomerValidationServiceFactory.GetStratedgy(customer.Type); validation.Valid(customer) but now I have a static method which needs to know how to initialize different services. I am sure this is a very common problem, What is the right way to solve this without changing service signatures or breaking DI?

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  • Software development magazines [closed]

    - by Sebastian
    Ive spent the last hour or so browsing the web for professional development magazines. I am mostly interested in the java platform, agile methods, "programming in general" (tutorials on languages or whatever, "hot new stuff" etc) and software craftmanship. My best finding yet was pragpub and maybe MSDN magazine. I am willing to pay and have a Zinio account if anyone knows a magazine about programming that is distributed by them. Ive already browsed a couple of related threads here on stackexchange. ACM and IEEE does not seem relevant, as Im not interested in research articles. Maybe conferences like OOPSLA as somebody mentioned in another thread. PS. I prefer if they are in pdf or readable on kindle or a tablet. DS. BR Sebastian

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  • Date calculation algorithm

    - by Julian Cuevas
    I'm working on a project to schedule a machine shop, basically I've got everything covered BUT date calculations, I've got a method called schedule (working on PHP here): public function schedule($start_date, $duration_in_minutes) Now my problem is, currently I'm calculating end time manually because time calculations have the following rules: During weekdays, work with business hours (7:00 AM to 5:00 PM) Work on Saturdays from 7:00 AM to 2:00 PM Ignore holidays (in Colombia we have A LOT of holidays) I already have a lookup table for holidays, I also have a Java version of this algorithm that I wrote for a previous version of the project, but that one's also manual. Is there any way to calculate an end time from a start time given duration?, my problem is that I have to consider the above rules, I'm looking for a (maybe?) math based solution, however I currently don't have the mind to devise such a solution myself. I'll be happy to provide code samples if necessary.

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  • How to Rotate different data in days of the week in php [migrated]

    - by shihon
    I am working on a project in which i have to distribute different ad's per day, the ad's in form of array are: $ad = array( 'attribute1_value' => "12", 'attribute2_value' => "xyz", 'attribute3_value' => 'http://example.com', 'attribute4_value' => 'data'); The logic i am using with switch case : $day = date('w',time()); switch ($day) { case '0': if($day == '0') { $count = 0; echo $ad; $count++; } else { $count = 7; echo $ad; } break; case '1': if($day == '1') { $count = 1; echo $ad; $count++; } else { $count = 8; echo $ad; } break; Problem is if i have ~15 ad's then i want to distribute ad/day, date('w') output's the present day but after day 7 i.e saturday, on sunday ad number 8 initiate. I have to implement this scenario using date function. Also i have to send ad's to those user who are not experience this ad before. I am not expert in php, as a beginner working in php/mysql. Kindly help me to improve this concept

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  • How to use correctly the comments in C/++

    - by Lucio
    I'm learning to program in C and in my stage, the best form to use correctly the comments is writing good comments from the beginning. As the comments are not just for that one understands better the code but others too, I want to know the views of all of you to reach a consensus. So what I want is that the most experienced users edit the following code as you please. (If it's unnecessary, delete it; If it's wrong, correct it; If needed, add more) Thus there'll be multiple answers with different syntax and the responses with the most votes will be taken as referring when commenting. The code to copy, paste and edit to your pleasure is: (And I remark again, just import the comments, not the code) /* This programs find 1 number in 1 file. The file is binary type and has integers in series. The number is integer type and it's entered from the keyboard. When finished the program, a poster will show the results: Saying if the number is in the file or not. */ #include <stdio.h> //FUNCTION 1 //Open file 'path' and closes it. void openf(char path[]) { int num; //Read from Keyboard a Number and it save it into 'num' var printf("Ready for read number.\n\nNumber --> "); fflush(stdin); scanf("%d",&num); //Open file 'path' in READ mode FILE *fvar; fvar=fopen(path,"rb"); //IF error happens when open file, exit of function if (fvar==NULL) { printf("ERROR while open file %s in read mode.",path); exit(1); } /*Verify the result of 'funct' function IF TRUE, 'num' it's in the file*/ if (funct(path,fvar,num)) printf("The number %d it is in the file %s.",num,path); else printf("The number %d it is not in the file %s.",num,path); fclose(fvar); } /*FUNCTION 2 It is a recursive function. Reads number by number until the file is empty or the number is found. Parameters received: 'path' -> Directory file 'fvar' -> Pointer file 'num' -> Number to compare */ int funct(char path[],FILE *fvar,int num) { int compare; //FALSE condition when the pointer reaches the end if (fread(&compare,sizeof(int),1,fvar)>0) /*TRUE condition when the number readed is iqual that 'num' ELSE will go to the function itself*/ if (compare!=num) funct(path,fvar,num); else return 1; else return 0; } int main(int argc, char **argv) { char path[30]="file.bin"; //Direction of the file to process openf(path); //Function with algorithm return 0; }

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  • What triggered the popularity of lambda functions in modern mainstream programming languages?

    - by Giorgio
    In the last few years anonymous functions (AKA lambda functions) have become a very popular language construct and almost every major / mainstream programming language has introduced them or is planned to introduce them in an upcoming revision of the standard. Yet, anonymous functions are a very old and very well-known concept in Mathematics and Computer Science (invented by the mathematician Alonzo Church around 1936, and used by the Lisp programming language since 1958, see e.g. here). So why didn't today's mainstream programming languages (many of which originated 15 to 20 years ago) support lambda functions from the very beginning and only introduced them later? And what triggered the massive adoption of anonymous functions in the last few years? Is there some specific event, new requirement or programming technique that started this phenomenon? IMPORTANT NOTE The focus of this question is the introduction of anonymous functions in modern, main-stream (and therefore, maybe with a few exceptions, non functional) languages. Also, note that anonymous functions (blocks) are present in Smalltalk, which is not a functional language, and that normal named functions have been present even in procedural languages like C and Pascal for a long time. Please do not overgeneralize your answers by speaking about "the adoption of the functional paradigm and its benefits", because this is not the topic of the question.

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  • Company wants to write custom project management tool, rather then use third party product.

    - by Jason Evans
    At the company I work, we are really wanting to get into the agile methodology for developing software. One thing that I'm not excited about is the fact that management wants us to build a custom project management feature inside the company's Intranet. I think this is a total waste of time. There are many great third party tools available (e.g. Axosoft OnTime) that can do everything we need, and more. For how much development time it would cost us to build our own project management module, we could buy numerous licences for a third party product. One concern is that, whilst we are writing code for a client, and using our custom Intranet project management module, we find bugs in the module that need fixing ASAP. That means having to stop work on the client code to fix the Intranet. That just puts shivers down my spine. Another worry I have is lack of functionality. This custom module is going to be so basic, that it will just feel really crap to use. That might sound a bit snooty, but for goodness sake, many third party tools are so feature rich, that the idea of having to write our own tool makes feel very uneasy. In fact, I can't be bothered. What do you guys think? I'm going to raise this issue with my boss, since I feel it's such an important topic to talk about. EDIT: Thanks for the great responses, much appreciated. To summarize some of them: Money Naturally my boss does want to save money, by not forking out a few hundred £'s for licences. However, for us to write a custom tool, it will take x number of days, multiplied by approx £500, which is our costs. I don't see the business value in this. Management have mentioned that they want to sell the Intranet as a product in the future, but it's so custom to our needs (and downright basic), that in order to give it to another client, I can see us having to fork a version of the code and rebuild the majority of it anyway. So it's not like we're gaining anything there in reuse. Features Having our own custom module means not feature bloat - only the functionality we require will be in the product. My issue is that there are plenty of free, open-source project management tools out there with minimal features already. So even if cost is an issue, we could look into open-source. Again it all boils down to the fact that I don't see the point in writing a project management tool in this day and age. It's a bit like writing your own web browser - why?, what's the point? Although management are asking for this tool, just because they are, it does not mean I'm going to please them and do it just because they asked for it. If something does not make sense, then I will raise it as a concern. At the end of the day, it's the developers who write the code, it's the developers who make money for a business. Thus, as far I'm concerned, the devs have a very big role in deciding how a company should manage projects and what tools are used. "I am Spartan, argh!" :) Hmm, I've not been able to make this question a wiki for some reason, thus I'm going to have to pick an answer to accept. Cheers. Jas.

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  • What effects do various drugs have on coding style / productivity? [closed]

    - by codecraft
    Can anyone tell me what the effect of various drugs are on coding style, and if coding on drugs can be more productive, or more fun? Are some types of drugs better suited to certain tasks and phases of software development? And which programming languages are best suited to coding on drugs? It would be great if you could back up your answers by data, probably even code snippets showcasing the effect of the drug experience.

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  • Is Windows 7 written in Xaml? [closed]

    - by Jordan
    Is Windows 7 written using Xaml? Edit Wow, so much hate for such a little question. I'm not an idiot. I know what XAML is. I use it every day. I was just curious whether some of the visual features were laid out with XAML, or if XAML was incorporated in some way to the product. I'm sorry if it is a programming sin not to know what Windows 7 was written in. I mean, I know Windows XP et al used C++/C, I've used Win32 quite a lot (and MFC and .NET).

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  • Internal and external API architecture

    - by Tacomanator
    The company I work for maintains a successful SaaS product that grew "organically" over the years. We are planning to expand the line with a suite of new products that will share data with the existing product. To support this, we are looking to consolidate business logic into a single place: a web service layer. The WS layer will be used by: The web applications A tool to import data A tool to integrate with other client software (not an API per se) We also want to create an API that can be used by our customers that are capable of using it to create their own integrations. We are struggling with the following question: Should the internal API (aka the WS layer) and the external API be one in the same, with security and permission settings to control what can be done by who, or should they be two separate applications where the external API just calls the internal API like any other application? So far in our debate it seems that separating them may be more secure, but will add overhead. What have others done in a similar situation?

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  • Cheerp -- C++ for web: advance or regression?

    - by Henrique Barcelos
    Recently I've run into Cheerp, a C++ to Javascript compiler, which uses a modified version of clang to generate Javascript code from C++ sources. That makes me wonder: why in the seven kingdoms would someone do this in their right mind? I mean: why would you take a language that is not designed for web at all, that is far more convoluted and bureaucratic, write your code and then compile it into Javascript itself? Can anybody see any advantages in doing so? We surely can discard performance as a reason, because in the end it generates pure Javascript code. Is there anyone here that have real experience with this? P.S.: I'm not sure if this is an on topic question, but this is the most general forum about programming that I could find in the StackExchange network. Edit Although this seems like a subjective question, it is not. I am asking for reasons that this tool could be useful. I got interested at first, but started wondering why would someone use it.

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  • What is the use of Association, Aggregation and Composition (Encapsulation) in Classes

    - by SahilMahajanMj
    I have gone through lots of theories about what is encapsulation and the three techniques of implementing it, which are Association, Aggregation and Composition. What i found is, Encapsulation Encapsulation is the technique of making the fields in a class private and providing access to the fields via public methods. If a field is declared private, it cannot be accessed by anyone outside the class, thereby hiding the fields within the class. For this reason, encapsulation is also referred to as data hiding. Encapsulation can be described as a protective barrier that prevents the code and data being randomly accessed by other code defined outside the class. Access to the data and code is tightly controlled by an interface. The main benefit of encapsulation is the ability to modify our implemented code without breaking the code of others who use our code. With this feature Encapsulation gives maintainability, flexibility and extensibility to our code. Association Association is a relationship where all object have their own lifecycle and there is no owner. Let’s take an example of Teacher and Student. Multiple students can associate with single teacher and single student can associate with multiple teachers but there is no ownership between the objects and both have their own lifecycle. Both can create and delete independently. Aggregation Aggregation is a specialize form of Association where all object have their own lifecycle but there is ownership and child object can not belongs to another parent object. Let’s take an example of Department and teacher. A single teacher can not belongs to multiple departments, but if we delete the department teacher object will not destroy. We can think about “has-a” relationship. Composition Composition is again specialize form of Aggregation and we can call this as a “death” relationship. It is a strong type of Aggregation. Child object dose not have their lifecycle and if parent object deletes all child object will also be deleted. Let’s take again an example of relationship between House and rooms. House can contain multiple rooms there is no independent life of room and any room can not belongs to two different house if we delete the house room will automatically delete. The question is: Now these all are real world examples. I am looking for some description about how to use these techniques in actual class code. I mean what is the point for using three different techniques for encapsulation, How these techniques could be implemented and How to choose which technique is applicable at time.

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  • Should extension scripts be run in a sandbox?

    - by Cubic
    In particular, this is about game extensions written in lua (luajit-2.0). I was contemplating whether I should restrict what these scripts can do, and arrived at the conclusion that I probably shouldn't: It's hard to get right. Sounds silly, but chances are my sandbox is gonna end up leaky anyways. The only benefit I could think of would be giving users some sense of security when running third party scripts. The disadvantages would be that it's just incredibly annoying for extension writers. That is, for now, myself (game content will be mostly scripted). The reason I'm asking this now before I actually have anything presentable is that adding a sandbox early on is easy, but would impose said annoying restrictions on myself too. However if I first go on with it and then later decide I do need a sandbox after all, I'm gonna run into problems (I'd either have to rewrite the scripts that are already there, or introduce some form of trust management system which seems to be more trouble than it's worth).

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  • Which Shopping Cart is better to run online grocery shop Prestrashop or nopCommerce

    - by Bigmunk
    I have been researching on open source software for an online grocery shop project. I have now narrowed by search to .NET based nopCommerce and the PHP based PrestaShop shopping carts. My plan is to acquire an open source shopping cart and hire a local developer to customize it to our local needs & as per our requirement. I'm now wondering whether I should have a developer start the whole project from scratch, or use an open source software such us PrestaShop or nopCommerce which can then be customized? Note that my store will have thousands of products and services so I want something that can handle up to 5000 products and over. Thanks for your thoughts and advice in advance.

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  • How to manage product backlog/user stories

    - by Andrew Stephens
    We're about to start a new project using Agile (using TFS), and I have a couple of "good practice" questions regarding the product backlog:- When we first start adding users stories, is it a good idea to put them in (say) a "Backlog" iteration, or just leave their iteration blank? Obviously when the time comes to start work on a US it would be moved into the appropriate iteration backlog. When breaking an epic down into smaller USs, would I simply close the original epic, as it's no longer required? Or should I create the new USs as children of the epic? (it's then someone's responsibility to close the epic once all child USs have been completed). Lastly, should the product backlog list all USs regardless of status, or only those that have not been started (i.e in my proposed "Backlog" iteration)? I realise these questions aren't life-or-death, but it would be nice to know how other people manage their product backlogs so we can organise things properly from the start.

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  • How to get better at solving Dynamic programming problems

    - by newbie
    I recently came across this question: "You are given a boolean expression consisting of a string of the symbols 'true', 'false', 'and', 'or', and 'xor'. Count the number of ways to parenthesize the expression such that it will evaluate to true. For example, there is only 1 way to parenthesize 'true and false xor true' such that it evaluates to true." I knew it is a dynamic programming problem so i tried to come up with a solution on my own which is as follows. Suppose we have a expression as A.B.C.....D where '.' represents any of the operations and, or, xor and the capital letters represent true or false. Lets say the number of ways for this expression of size K to produce a true is N. when a new boolean value E is added to this expression there are 2 ways to parenthesize this new expression 1. ((A.B.C.....D).E) ie. with all possible parenthesizations of A.B.C.....D we add E at the end. 2. (A.B.C.(D.E)) ie. evaluate D.E first and then find the number of ways this expression of size K can produce true. suppose T[K] is the number of ways the expression with size K produces true then T[k]=val1+val2+val3 where val1,val2,val3 are calculated as follows. 1)when E is grouped with D. i)It does not change the value of D ii)it inverses the value of D in the first case val1=T[K]=N.( As this reduces to the initial A.B.C....D expression ). In the second case re-evaluate dp[K] with value of D reversed and that is val1. 2)when E is grouped with the whole expression. //val2 contains the number of 'true' E will produce with expressions which gave 'true' among all parenthesized instances of A.B.C.......D i) if true.E = true then val2 = N ii) if true.E = false then val2 = 0 //val3 contains the number of 'true' E will produce with expressions which gave 'false' among all parenthesized instances of A.B.C.......D iii) if false.E=true then val3=( 2^(K-2) - N ) = M ie. number of ways the expression with size K produces a false [ 2^(K-2) is the number of ways to parenthesize an expression of size K ]. iv) if false.E=false then val3 = 0 This is the basic idea i had in mind but when i checked for its solution http://people.csail.mit.edu/bdean/6.046/dp/dp_9.swf the approach there was completely different. Can someone tell me what am I doing wrong and how can i get better at solving DP so that I can come up with solutions like the one given above myself. Thanks in advance.

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