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  • Right design to validate attributes of a class instance

    - by systempuntoout
    Having a simple Python class like this: class Spam(object): __init__(self, description, value): self.description = description self.value = value Which is the correct approach to check these constraints: "description cannot be empty" "value must be greater than zero" Should i: 1.validate data before creating spam object ? 2.check data on __init__ method ? 3.create an is_valid method on Spam class and call it with spam.isValid() ? 4.create an is_valid static method on Spam class and call it with Spam.isValid(description, value) ? 5.check data on setters? 6.... Could you recommend a well designed\Pythonic\not verbose (on class with many attributes)\elegant approach?

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  • "Overriding" instance variables in subtype: Possible risks?

    - by sebastiangeiger
    Say I had a class SuperClass and two subclasses SubClassA and SubClassB that inherit from SuperClass. abstract class SuperClass{ ... List someList; ... } class SubClassA extends SuperClass{ ... List<String> someList; ... } class SubClassB extends SuperClass{ ... List<Integer> someList; ... } That way it is convenient because I can get someList.size() in Superclass and have Typesafety in the Subclasses. The problem is that it does not "feel" right, can you think of potential hazards this apporach has that I am not aware of?

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  • Ruby on Rails: instance & class variables not maintaining value in controller

    - by DerNalia
    at the top of my controller, outside of any method, I have @@javascript_is_disabled = false and I have methods that that the view calls and invokes something like this @@javascript_is_disabled = params[:javascript_disabled] but when I need the @@javascript_is_disabled in completely different method.. it is always false. I know it changes in the method with params args... cause those methods behave differently, and appropriately And ideas?

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  • StructureMap IoC problem getting the instance in runtime

    - by user274269
    i have 2 concrete types "CategoryFilter" & "StopWordsFilter" that implements "IWordTokensFilter". Below is my setup: ForRequestedType<IWordTokensFilter>().TheDefaultIsConcreteType<CategoryFilter>() .AddInstances(x => { x.OfConcreteType<StopWordsFilter>(); } ); The problem is the run-time when structure map auto inject it on my class, bec. i have arguments with same plugin-type: public ClassA(IWordTokensFilter stopWordsFilter, IWordTokensFilter categoryFilter) i'm always getting CategoryFilter in my first argument but it should be stopWordsFilter. How can i setup this in a right way? thanks in advance

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  • C++ calculation evaluated to 0

    - by Alexander Stolz
    I'm parsing a file and trying to decode coordinates to the right unit. What happens is that this code is evaluated to 0. If I type it into gdb the result is correct. int pLat = (int)( (argv[6].data() == "plus" ? 1 : -1) * ( atoi(argv[7].data()) + atoi(argv[8].data()) / 60. + atoi(argv[9].data()) / 36000.) * 2.145767 * 0.0001); P.s. If someone knows a better title for this question, please change it

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  • What is the best design to this class?

    - by HPT
    assume this class: public class Logger { static TextWriter fs = null; public Logger(string path) { fs = File.CreateText(path); } public static void Log(Exception ex) { ///do logging } public static void Log(string text) { ///do logging } } and I have to use this like: Logger log = new Logger(path); and then use Logger.Log() to log what I want. the question is: is this a good design? to instantiate a class and then always call it's static method? any suggestion yield in better design is appreciated.

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  • Can a function/class know the context from where it is being invoked or instantiated?

    - by vrode
    Let's take this class as example and assume that get_context() returns the source of the call: class A { public function __construct( ) { if( get_class( get_context( ) ) == B ) { return true; } else { return false; } } } class B { function __construct( ) { $a = new A( ); } } $a = new B( ); // returns true, as B is the invoking class of A $a = new A( ); // returns false, as B is invoked outside of any class So, my questions are: 1) can a function know the context that calls it? 2) can a object know context from where it has been instantiated? Or am I dreaming up new features not implementable in PHP?

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  • C++ Compound Interest Exercise

    - by Lameste
    I'm a beginner trying to learn C++ using "C++ Primer Plus Sixth Edition". I'm on Chapter 5, going over loops. Anyways I was doing this programming exercise from the book, the problem is: Daphne invests $100 at 10% simple interest.That is, every year, the investment earns 10% of the original investment, or $10 each and every year: interest = 0.10 × original balance At the same time, Cleo invests $100 at 5% compound interest.That is, interest is 5% of the current balance, including previous additions of interest: interest = 0.05 × current balance Cleo earns 5% of $100 the first year, giving her $105.The next year she earns 5% of $105, or $5.25, and so on.Write a program that finds how many years it takes for the value of Cleo’s investment to exceed the value of Daphne’s investment and then displays the value of both investments at that time. Here is the code I have written for this exercise, I'm not getting good results though. #include <iostream> #include <array> double Daphne(int, double, double); double Chleo(double, double); int main() { using namespace std; int p = 100; //Principle double i1 = 0.1; // 10% interest rate double i2 = 0.05; // 5% interest rate double dInv = 0; //Daphnes investment double cInv = 0; // Chleos investment int t=1; //Starting at year 1 double s1 = 0; //Sum 1 for Daphne double s2 = 0; // Sum 2 for Chleo s1 = p + 10; //Initial interest (base case after year 1) for Daphne s2 = p + (i2*p); //Initial interest (base case after year 1) for Chleo /*cout << s1 << endl; cout << s2 << endl;*/ while (cInv < dInv) { dInv = Daphne(p, i1, s1); cInv = Chleo(i2, s2); t++; } cout << "The time taken for Chleos investment to exceed Daphnes was: " << t << endl; cout << "Daphnes investment at " << t << " years is: " << dInv << endl; cout << "Chleos invesment at " << t << " years is: " << cInv << endl; system("pause"); return 0; } double Daphne(int p, double i, double s1) { s1 = s1 + (p*i); return s1; } double Chleo(double i, double s2){ s2 = s2 + (s2*i); return s2; } Output from console: The time taken for Chleos investment to exceed Daphnes was: 1 Daphnes investment at 1 years is: 0 Chleos invesment at 1 years is: 0 Press any key to continue . . . Can anyone explain why I'm getting this current result? The while loop is supposed to continue executing statements until Chleo's investment exceeds Daphnes.

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  • Are doubles faster than floats in c#?

    - by Trap
    I'm writing an application which reads large arrays of floats and performs some simple operations with them. I'm using floats because I thought it'd be faster than doubles, but after doing some research I've found that there's some confusion about this topic. Can anyone elaborate on this? Thanks.

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  • Fetching a result twice with deferend name

    - by user1799842
    I have 1 table with tasks named opentask:columns: id,title,description,expires,creator_id,creator_name, executer_id, executer_name, priority_id, status_id1 table with users named user: with columns: user_id, username What I want is to create a query where there will be all columns from opentask table where the executer_id will be equal to the user_id of user table AND the creator_id will be equal to the user_id again. This creates a confusion because the first equality excludes the second.So I need somehow to create a query where I will include the usernames for the executer with something like where "opentask.executer_id=user_user_id" and at the same time I will include the username again (as a differend name?) for the creator with something like "where opentask.executer_id=user_user_id"So I try this, which of course I know that is missing something, can you help? SELECT DISTINCT id, title, description, expires, creator_id, executer_id, oc_opentask.priority_id, oc_opentask.status_id, priority_name, status_name, user_id, username, (SELECT username FROM oc_opentask, oc_user WHERE oc_opentask.creator_id=oc_user.user_id) AS username2 FROM oc_opentask, oc_opentask_priority, oc_user, oc_opentask_status WHERE oc_opentask.priority_id=oc_opentask_priority.priority_id AND oc_opentask.executer_id=oc_user.user_id AND oc_opentask.status_id=oc_opentask_status.status_id ORDER BY oc_opentask.expires DESC

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  • Returning and instance of a Class given its .class (MyClass.class)

    - by jax
    I have an enum that will hold my algorithms. I cannot instantiate these classes because I need the application context which is only available once the application has started. I want to load the class at runtime when I choose by calling getAlgorithm(Context cnx). How do I easily instantiate a class at runtime given its .class (and my constructor takes arguments)? All my classes are subclasses of Algorithm. public enum AlgorithmTypes { ALL_FROM_9_AND_LAST_FROM_10_ID(AlgorithmFactory.AlgorithmAllFrom9AndLastFrom10Impl.class), ALL_FROM_9_AND_LAST_FROM_10_CURRENCY_ID(AlgorithmFactory.AlgorithmAllFrom9AndLastFrom10Impl.class), DIVIDE_BY_9_LESS_THAN_100(AlgorithmFactory.AlgorithmAllFrom9AndLastFrom10Impl.class), TABLES_BEYOND_5_BY_5(AlgorithmFactory.AlgorithmAllFrom9AndLastFrom10Impl.class); private Class<? extends Algorithm> algorithm; AlgorithmTypes(Class<? extends Algorithm> c) { algorithm = c; } public Algorithm getAlgorithm(Context cnx) { return //needs to return the current algoriths constructor which takes the Context Algorithm(Context cnx); } }

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  • How to get a list of users for all instance's databases

    - by stee1rat
    I guess the procedure should be something like this: declare @db varchar(100) declare @user varchar(100) declare c cursor for select name from sys.sysdatabases open c fetch next from c into @db while @@fetch_status = 0 begin print @db exec ('use ' + @db) declare u cursor for select name from sys.sysusers where issqlrole <> 1 and hasdbaccess <> 0 and isntname <> 1 open u fetch next from u into @user while @@fetch_status = 0 begin print @user fetch next from u into @user end print '--------------------------------------------------' close u deallocate u fetch next from c into @db end close c deallocate c But the problem is that exec ('use ' + @db) doesn't work. And i always get user list of currently chosen database. How should i fix that? P.S.: I want this code to work on both 2000 and 2005 sql servers.

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  • Create a new instance in a static function of an abstract class

    - by arno
    abstract class db_table { static function get_all_rows() { ... while(...) { $rows[] = new self(); ... } return $rows; } } class user extends db_table { } $rows = user::get_all_rows(); I want to create instances of a class from a static method defined in the abstract parent class but PHP tells me "Fatal error: Cannot instantiate abstract class ..." How should I implement it correctly?

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  • Detect if an instance is running with kernel32::CreateMutexA

    - by moz
    Hello. I'm working on an NSIS installer, and trying to check if a certain application is running before uninstalling. So, I use kernel32::CreateMutexA call. Here is the chunk: System::Call 'kernel32::CreateMutexA(i 0, i 0, t "cmd.exe") i .r1 ?e' Pop $R0 StrCmp $R0 0 +3 MessageBox MB_USERICON "The application is already running." Abort I put it into un.onInit. Trouble is, the process (cmd.exe here) is never detected. Did I miss something? Tx.

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  • how to generate the instance for logger?

    - by Elakkiya
    Here is my code package com.my; import org.apache.log4j.spi.LoggerFactory; import java.io.*; import java.util.logging.*; public class Log { public static void main(String[] args) { try{ FileHandler hand = new FileHandler("vk.log"); Logger log = Logger.getLogger("log_file"); log.addHandler(hand); log.warning("Doing carefully!"); log.info("Doing something ..."); log.severe("Doing strictily "); System.out.println(log.getName()); } catch(IOException e){ System.out.println(e) } } }

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  • Reference to an instance method of a particular object

    - by Andrey
    In the following code, if i try to pass method reference using the class name, works. But passing the reference variable compiler gives an error, i do not understand why? public class User { private String name; public User(String name) { this.name = name; } public void printName() { System.out.println(name); } } public class Main { public static void main(String[] args) { User u1 = new User("AAA"); User u2 = new User("BBB"); User u3 = new User("ZZZ"); List<User> userList = Arrays.asList(u1, u2, u3); userList.forEach(User::printName); // works userList.forEach(u1::printName); // compile error } } Thanks,

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  • Correct Path for Git Remote Add from Amazon EC2 Instance to OSX Client Machine

    - by filmnut
    I'm trying to do a git remote add from a repository that sits on a remote Amazon AMI back to a cloned copy of the SAME repository that is sitting on my local OSX machine. I'm confused about what file path to use. I assume it's something like: git remote add my_clone <OSX_User_Name>@<OSX_HOST_NAME>:<PATH_TO_CLONED_REPO> I obviously know what my <OSX_User_Name> is, and I can figure out my <PATH_TO_CLONED_REPO>, but I have no idea how to determine a <OSX_HOST_NAME> that would actually work. Can I just put in my external IP address, followed by my machine's internal IP address? (Note that I'm working behind a router.) Is ssh:// the correct protocol? Do I need to set up ssh access from the Amazon EC2 machine to the local OSX machine?

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  • Android Static Variable Scope and Lifetime

    - by Edison
    I have an application that has a Service uses a ArrayList to store in the background for a very long time, the variable is initialized when the service started. The service is in the background and there will be frequent access to the variable (that's why i don't want to use file management or settings since it will be very expensive for a file I/O for the sake of battery life). The variable will likely to be ~1MB-2MB over its life tie. Is it safe to say that it will never be nulled by GC or the system or is there any way to prevent it? Thanks.

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