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  • Beginner having a problem with classes

    - by David
    I'm working through O'Reilly's "Learning Python" and having a problem with classes. I think I understand the concept, but in practice have stumbled upon this problem. Fron page 88-89: >>> class Worker: def __innit__(self, name, pay): self.name=name self.pay=pay def lastName(self): return self.name.split()[-1] def giveRaise(self, percent): self.pay*=(1.0+percent) Then the book says "Calling the class like a function generates instances of a new type ...etc" and gives this example. bob = Worker('Bob Smith', 50000) This gives me this error: TypeError: this constructor takes no arguments. And then I start muttering profanities. So what am I doing wrong here? Thanks for the help.

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  • doubt about radio button mysql php beginner

    - by Marcelo
    Hi, i'm an engineering student and i'm developing a simple software based on html,php and mysql. I learned this topics on w3schools, i know only the basics. I tired to search about this in this website but I thought the doubts about php,mysql, radio buttons but they were much more complex than I need, and that i could understand. Sorry for the english. (Q1)Ex: $email=$_REQUEST['email'] , in this case the input is text, if it where like a radio button for ex: sex: male or female, how would it be? (Q2) what would be the type of this field (for exemple sex in question 1) in the database: text, int, varchar ? thanks for the attention

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  • Python beginner confused by a complex line of code

    - by Protean
    I understand the gist of the code, that it forms permutations; however, I was wondering if someone could explain exactly what is going on in the return statement. def perm(l): sz = len(l) print (l) if sz <= 1: print ('sz <= 1') return [l] return [p[:i]+[l[0]]+p[i:] for i in range(sz) for p in perm(l[1:])]

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  • How is Java Platform independent when it needs JVM to run ?

    - by happysoul
    Just started learning Java and I am confused about this whole independent platform thingy. Doesn't independent means that Java code should be able to run on any machine and would need no special software to be installed (JVM in this case has to be present in the machine)? Like, for example, we need to have Turbo C Compiler in order to compile C/C++ source code and then execute it.. The machine has to have the C compiler. guess I am confused..Somebody please explain in simple language or may be direct me to a tutorial that explain things in simple language ? that would be great I am just not getting the concept.

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  • Python beginner, strange output problem

    - by Protean
    I'm having a weird problem with the following piece of code. from math import sqrt def Permute(array): result1 = [] result2 = [] if len(array) <= 1: return array for subarray in Permute(array[1:]): for i in range(len(array)): temp1 = subarray[:i]+array[0]+subarray[i:] temp2 = [0] for num in range(len(array)-1): temp2[0] += (sqrt(pow((temp1[num+1][1][0]-temp1[num][1][0]),2) + pow((temp1[num+1][1][1]-temp1[num][1][1]),2))) result1.append(temp1+temp2) return result1 a = [['A',[50,1]]] b = [['B',[1,1]]] c = [['C',[100,1]]] array = [a,b,c] result1 = Permute(array) for i in range(len(result1)): print (result1[i]) print (len(result1)) What it does is find all the permutations of the points abc and then returns them along with the sum of the distances between each ordered point. It does this; however, it also seems to report a strange additional value, 99. I figure that the 99 is coming from the computation of the distance between point a and c but I don't understand why it is appearing in the final output as it does.

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  • Validating Age field javascript beginner

    - by Marcelo
    Hi people, I'm trying to validate an age field in a form but I'm having some problem. First I tried to make sure that the field will not be send empty. I don't know javascript so I searched some scripts and adapted them to this: function isInteger (s) { var i; if (isEmpty(s)) if (isInteger.arguments.length == 1) return 0; else return (isInteger.arguments[1] == true); for (i = 0; i < s.length; i++) { var c = s.charAt(i); if (!isDigit(c)) return false; } return true; } function isEmpty(s) { return ((s == null) || (s.length == 0)) } function validate_required(field,alerttxt) { with (field) { if (value==null||value=="") { alert(alerttxt);return false; } else { return true; } } } function validate_form(thisform) { with (thisform) { if ((validate_required(age,"Age must be filled out!")==false) || isInteger(age,"Age must be and int number")==false)) {email.focus();return false;} } } //html part <form action="doador.php" onsubmit="return validate_form(this)" method="post"> It's working fine for empty fields, but if I type any letters or characters in age field, it'll be sent and saved a 0 in my database. Can any one help me ? Sorry for any mistake in English, and thanks in andvance for your help.

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  • Beginner to RUBY - Array Question

    - by WANNABE
    a = [ 1, 3, 5, 7, 9 ] ? [1, 3, 5, 7, 9] a[2, 2] = ’cat’ ? [1, 3, "cat", 9] a[2, 0] = ’dog’ ? [1, 3, "dog", "cat", 9] a[1, 1] = [ 9, 8, 7 ] ? [1, 9, 8, 7, "dog", "cat", 9] a[0..3] = [] ? ["dog", "cat", 9] a[5..6] = 99, 98 ? ["dog", "cat", 9, nil, nil, 99, 98] I can understand how the last four amendments to this array work, but why do they use a[2, 2] = 'cat' and a[2,0] = 'dog' ??? What do the two numbers represent? Couldnt they just use a[2] = 'dog'?

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  • TDD - beginner problems and stumbling blocks

    - by Noufal Ibrahim
    While I've written unit tests for most of the code I've done, I only recently got my hands on a copy of TDD by example by Kent Beck. I have always regretted certain design decisions I made since they prevented the application from being 'testable'. I read through the book and while some of it looks alien, I felt that I could manage it and decided to try it out on my current project which is basically a client/server system where the two pieces communicate via. USB. One on the gadget and the other on the host. The application is in Python. I started off and very soon got entangled in a mess of rewrites and tiny tests which I later figured didn't really test anything. I threw away most of them and and now have a working application for which the tests have all coagulated into just 2. Based on my experiences, I have a few questions which I'd like to ask. I gained some information from http://stackoverflow.com/questions/1146218/new-to-tdd-are-there-sample-applications-with-tests-to-show-how-to-do-tdd but have some specific questions which I'd like answers to/discussion on. Kent Beck uses a list which he adds to and strikes out from to guide the development process. How do you make such a list? I initially had a few items like "server should start up", "server should abort if channel is not available" etc. but they got mixed and finally now, it's just something like "client should be able to connect to server" (which subsumed server startup etc.). How do you handle rewrites? I initially selected a half duplex system based on named pipes so that I could develop the application logic on my own machine and then later add the USB communication part. It them moved to become a socket based thing and then moved from using raw sockets to using the Python SocketServer module. Each time things changed, I found that I had to rewrite considerable parts of the tests which was annoying. I'd figured that the tests would be a somewhat invariable guide during my development. They just felt like more code to handle. I needed a client and a server to communicate through the channel to test either side. I could mock one of the sides to test the other but then the whole channel wouldn't be tested and I worry that I'd miss that. This detracted from the whole red/green/refactor rhythm. Is this just lack of experience or am I doing something wrong? The "Fake it till you make it" left me with a lot of messy code that I later spent a lot of time to refactor and clean up. Is this the way things work? At the end of the session, I now have my client and server running with around 3 or 4 unit tests. It took me around a week to do it. I think I could have done it in a day if I were using the unit tests after code way. I fail to see the gain. I'm looking for comments and advice from people who have implemented large non trivial projects completely (or almost completely) using this methodology. It makes sense to me to follow the way after I have something already running and want to add a new feature but doing it from scratch seems to tiresome and not worth the effort. P.S. : Please let me know if this should be community wiki and I'll mark it like that. Update 0 : All the answers were equally helpful. I picked the one I did because it resonated with my experiences the most. Update 1: Practice Practice Practice!

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  • Beginner assembly programming memory usage question

    - by Daniel
    I've been getting into some assembly lately and its fun as it challenges everything i have learned. I was wondering if i could ask a few questions When running an executable, does the entire executable get loaded into memory? From a bit of fiddling i've found that constants aren't really constants? Is it just a compiler thing? const int i = 5; _asm { mov i, 0 } // i is now 0 and compiles fine So are all variables assigned with a constant value embedded into the file as well? Meaning: int a = 1; const int b = 2; void something() { const int c = 3; int d = 4; } Will i find all of these variables embedded in the file (in a hex editor or something)? If the executable is loaded into memory then "constants" are technically using memory? I've read around on the net people saying that constants don't use memory, is this true?

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  • Java: how to have global values inside a class?

    - by HH
    I want less methods. I want a common global TestClass from which I could use any of its value inside the class. import java.util.*; import java.io.*; public class TestClass { TestClass(String hello){ String hallo = hello; String halloSecond = "Saluto!"; } public static void main(String[] args) { TestClass test = new TestClass("Tjena!"); System.out.println("I want "Tjena!": " + test.hallo); TestClass testSecond = new TestClass("1"); System.out.println("I want Saluto!:" + test.halloSecond); System.out.println("I want Saluto!:" + testSecond.halloSecond); // How can I get glob.vars like the "Saluto!"? } }

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  • C++ Beginner - 'friend' functions and << operator overloading: What is the proper way to overload an

    - by Francisco P.
    Hello, everyone! In a project I'm working on, I have a Score class, defined below in score.h. I am trying to overload it so, when a << operation is performed on it, _points + " " + _name is returned. Here's what I tried to do: ostream & Score::operator<< (ostream & os, Score right) { os << right.getPoints() << " " << right.scoreGetName(); return os; } Here are the errors returned: 1>c:\users\francisco\documents\feup\1a2s\prog\projecto3\projecto3\score.h(30) : error C2804: binary 'operator <<' has too many parameters (This error appears 4 times, actually) I managed to get it working by declaring the overload as a friend function: friend ostream & operator<< (ostream & os, Score right); And removing the Score:: from the function declaration in score.cpp (effectively not declaring it as a member). Why does this work, yet the code describe above doesn't? Thanks for your time! Below is the full score.h /////////////////////////////////////////////////////////// // Score.h // Implementation of the Class Score // Created on: 10-Mai-2010 11:43:56 // Original author: Francisco /////////////////////////////////////////////////////////// #ifndef SCORE_H_ #define SCORE_H_ #include <string> #include <iostream> #include <iostream> using std::string; using std::ostream; class Score { public: Score(string name); Score(); virtual ~Score(); void addPoints(int n); string scoreGetName() const; int getPoints() const; void scoreSetName(string name); bool operator>(const Score right) const; ostream & operator<< (ostream & os, Score right); private: string _name; int _points; }; #endif

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  • Beginner SQL section: avoiding repeated expression

    - by polygenelubricants
    I'm entirely new at SQL, but let's say that on the StackExchange Data Explorer, I just want to list the top 15 users by reputation, and I wrote something like this: SELECT TOP 15 DisplayName, Id, Reputation, Reputation/1000 As RepInK FROM Users WHERE RepInK > 10 ORDER BY Reputation DESC Currently this gives an Error: Invalid column name 'RepInK', which makes sense, I think, because RepInK is not a column in Users. I can easily fix this by saying WHERE Reputation/1000 > 10, essentially repeating the formula. So the questions are: Can I actually use the RepInK "column" in the WHERE clause? Do I perhaps need to create a virtual table/view with this column, and then do a SELECT/WHERE query on it? Can I name an expression, e.g. Reputation/1000, so I only have to repeat the names in a few places instead of the formula? What do you call this? A substitution macro? A function? A stored procedure? Is there an SQL quicksheet, glossary of terms, language specification, anything I can use to quickly pick up the syntax and semantics of the language? I understand that there are different "flavors"?

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  • Beginner C++ - Trouble using global constants in a header file

    - by Francisco P.
    Hello! Yet another Scrabble project question... This is a simple one. It seems I am having trouble getting my global constants recognized: My board.h: http://pastebin.com/R10HrYVT Errors returned: 1>C:\Users\Francisco\Documents\FEUP\1A2S\PROG\projecto3\projecto3\Board.h(34): error: variable "TOTAL_ROWS" is not a type name 1> vector< vector<Cell> > _matrix(TOTAL_ROWS , vector<Cell>(TOTAL_COLUMNS)); 1> 1>main.cpp 1>compilation aborted for .\Game.cpp (code 2) 1>Board.cpp 1>.\Board.h(34): error: variable "TOTAL_ROWS" is not a type name 1> vector< vector<Cell> > _matrix(TOTAL_ROWS , vector<Cell>(TOTAL_COLUMNS)); 1> ^ 1> Why does this happen? Why is the compiler expecting types? Thanks for your time!

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  • C# Keyboard Input (Beginner Help)

    - by ThickBook
    I am trying to ask user "enter any key and when that key is pressed it shows that "You Pressed "Key". Can you help what's wrong in this code? This is what I have written using System; class Program { public static void Main(string[] args) { Console.Write("Enter any Key: "); char name = Console.Read(); Console.WriteLine("You pressed {0}", name); } }

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  • Beginner += in Ruby

    - by WANNABE
    Looking at this block, I can follow the whole program until I hit, sum += square. What is he point of this line, what does it say??? sum = 0 [1, 2, 3, 4].each do |value| square = value * value sum += square end puts sum

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  • Beginner PHP: I can't insert data into MYSQL database

    - by Victor
    I'm learning PHP right now and I'm trying to insert data into a MySQL database called "pumpl2" The table is set up like this. create table product ( productid int unsigned not null auto_increment primary key, price int(9) not null, value int(9) not null, description text ); I have a form and want to insert the fields from the form in the database. Here is what the php file looks like. <?php // create short variable names $price = $_POST['price']; $value = $_POST['value']; $description = $_POST['description']; if (!$price || !$value || !$description) { echo "You have not entered all the required details.<br />" ."Please go back and try again."; exit; } @ $db = new mysqli('localhost', 'pumpl', '********', 'pumpl2'); if (mysqli_connect_errno()) { echo "Error: Could not connect to database. Please try again later."; exit; } $query = "insert into pumpl2 values ('".$price."', '".$value."', '".$description."')"; $result = $db->query($query); if ($result) { echo $db->affected_rows." product inserted into database."; } else { echo "An error has occurred. The item was not added."; } $db->close(); ?> When I submit the form, I get an error message "An error has occurred. The item was not added." Does anyone know what the problem is? Thank you!

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  • Beginner questions regarding Python classes.

    - by Andy
    Hi. I am new to Python so please don't flame me if I ask something too noobish :) 1. Consider I have a class: class Test: def __init__(self, x, y): self.x = x self.y = y def wow(): print 5 * 5 Now I try to create an object of the class: x = Test(3, 4) This works as expected. However, when I try to call the method wow(), it returns an error, which is fixed by changing wow() to: def wow(self) Why do I need to include self and if I don't, what does the method mean?2. In the definition of __init__: def __init__(self, x, y): self.x = x self.y = y Why do I need to declare x and y, when I can do this: def __init__(self): self.x = x self.y = y I hope I am being clear... Thanks for your time.

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  • what is a fun beginner project?

    - by Atticum
    I am learning HTML and I have a good book to learn with but my cousin told me that I should pick a fun project to learn how to program but im not sure what I should do. what is the most fun project to do when you are learning HTML?

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  • Quick, Beginner C++ Overloading Question - Getting the compiler to perceive << is defined for a spec

    - by Francisco P.
    Hello everyone. I edited a post of mine so I coul I overloaded << for a class, Score (defined in score.h), in score.cpp. ostream& operator<< (ostream & os, const Score & right) { os << right.getPoints() << " " << right.scoreGetName(); return os; } (getPoints fetches an int attribute, getName a string one) I get this compiling error for a test in main(), contained in main.cpp binary '<<' : no operator found which takes a right-hand operand of type 'Score' (or there is no acceptable conversion) How come the compiler doesn't 'recognize' that overload as valid? (includes are proper) Thanks for your time.

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  • C++ Beginner - Trouble using structs and constants!

    - by Francisco P.
    Hello everyone! I am currently working on a simple Scrabble implementation for a college project. I can't get a part of it to work, though! Check this out: My board.h: http://pastebin.com/J9t8VvvB The subroutine where the error lies: //Following snippet contained in board.cpp //I believe the function is self-explanatory... //Pos is a struct containing a char, y, a int, x and an orientation, o, which is not //used in this particular case void Board::showBoard() { Pos temp; temp.o = 0; for (temp.y = 'A'; temp.y < (65 + TOTAL_COLUMNS); ++temp.y) { for (temp.x = 1; temp-x < (1 + TOTAL_ROWS); ++temp.x) { cout << _matrix[temp].getContents(); } cout << endl; } } The errors returned on compile time: http://pastebin.com/bZv7fggq How come the error states that I am trying to compare two Pos when I am comparing chars and ints? I also really can't place these other errors... Thanks for your time!

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  • Beginner: Best Practices in an Android App UI Navagation

    - by AndyD273
    I am trying to learn how to do stuff in Android, and I'm not sure of the best way to build the interface. I've been working on porting an iPhone app, which uses navigation controllers and table views for looking at the different sections: basically, someone touches a cell in the table, which drills down to another table. when they touch a cell on that table it drills down to a webview that displays the information. I want to do something similar for the android app, but I don't know how, or if there is a better way native to Android. I've figured out how to use the webview to my purposes, but moving forward and backward in the table tree is unclear.

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  • Hardest concept to grasp as a beginner

    - by noizetoys
    When you were starting to program, what was the hardest concept for you to grasp? Was it recursion, pointers, linked lists, assignments, memory management? I was wondering what gave you headaches and how you overcame this issue and learned to love the bomb, I mean understand it. EDIT: As a followup, what helped you grok your hard-to-grasp concept?

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