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• Error with python-setuptools doing "sudo easy_install python-graph-core"

  - by Dan

  Using easy_install, part of the python-setuptools, I get the following error: $ sudo easy_install python-graph-core [sudo] password for dan: Searching for python-graph-core Reading http://pypi.python.org/simple/python-graph-core/ Reading http://code.google.com/p/python-graph/ Reading http://code.google.com/p/python-graph/downloads/list?can=1 Reading http://code.google.com/p/python-graph/downloads/list Best match: python-graph-core 1.7.0 Downloading http://python-graph.googlecode.com/files/python-graph-core-1.7.0.tar.gz Processing python-graph-core-1.7.0.tar.gz Running python-graph-core-1.7.0/setup.py -q bdist_egg --dist-dir /tmp/easy_install-GwpYiM/python-graph-core-1.7.0/egg-dist-tmp-1yqbyV setup.py:8: Warning: 'as' will become a reserved keyword in Python 2.6 Traceback (most recent call last): File "/usr/bin/easy_install", line 8, in <module> load_entry_point('setuptools==0.6c9', 'console_scripts', 'easy_install')() File "/usr/lib/python2.5/site-packages/setuptools/command/easy_install.py", line 1671, in main with_ei_usage(lambda: File "/usr/lib/python2.5/site-packages/setuptools/command/easy_install.py", line 1659, in with_ei_usage return f() File "/usr/lib/python2.5/site-packages/setuptools/command/easy_install.py", line 1675, in <lambda> distclass=DistributionWithoutHelpCommands, **kw File "/usr/lib/python2.5/distutils/core.py", line 151, in setup dist.run_commands() File "/usr/lib/python2.5/distutils/dist.py", line 974, in run_commands self.run_command(cmd) File "/usr/lib/python2.5/distutils/dist.py", line 994, in run_command cmd_obj.run() File "/usr/lib/python2.5/site-packages/setuptools/command/easy_install.py", line 211, in run self.easy_install(spec, not self.no_deps) File "/usr/lib/python2.5/site-packages/setuptools/command/easy_install.py", line 446, in easy_install return self.install_item(spec, dist.location, tmpdir, deps) File "/usr/lib/python2.5/site-packages/setuptools/command/easy_install.py", line 476, in install_item dists = self.install_eggs(spec, download, tmpdir) File "/usr/lib/python2.5/site-packages/setuptools/command/easy_install.py", line 655, in install_eggs return self.build_and_install(setup_script, setup_base) File "/usr/lib/python2.5/site-packages/setuptools/command/easy_install.py", line 930, in build_and_install self.run_setup(setup_script, setup_base, args) File "/usr/lib/python2.5/site-packages/setuptools/command/easy_install.py", line 919, in run_setup run_setup(setup_script, args) File "/usr/lib/python2.5/site-packages/setuptools/sandbox.py", line 27, in run_setup lambda: execfile( File "/usr/lib/python2.5/site-packages/setuptools/sandbox.py", line 63, in run return func() File "/usr/lib/python2.5/site-packages/setuptools/sandbox.py", line 29, in <lambda> {'__file__':setup_script, '__name__':'__main__'} File "setup.py", line 8 except ImportError as ie: ^ SyntaxError: invalid syntax Any suggestions to what I may be doing wrong? Thanks, Dan

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• Functional Adaptation

  - by Charles Courchaine

  In real life and OO programming we’re often faced with using adapters, DVI to VGA, 1/4” to 1/8” audio connections, 110V to 220V, wrapping an incompatible interface with a new one, and so on.  Where the adapter pattern is generally considered for interfaces and classes a similar technique can be applied to method signatures.  To be fair, this adaptation is generally used to reduce the number of parameters but I’m sure there are other clever possibilities to be had.  As Jan questioned in the last post, how can we use a common method to execute an action if the action has a differing number of parameters, going back to the greeting example it was suggested having an AddName method that takes a first and last name as parameters.  This is exactly what we’ll address in this post. Let’s set the stage with some review and some code changes.  First, our method that handles the setup/tear-down infrastructure for our WCF service: 1: private static TResult ExecuteGreetingFunc<TResult>(Func<IGreeting, TResult> theGreetingFunc) 2: { 3: IGreeting aGreetingService = null; 4: try 5: { 6: aGreetingService = GetGreetingChannel(); 7: return theGreetingFunc(aGreetingService); 8: } 9: finally 10: { 11: CloseWCFChannel((IChannel)aGreetingService); 12: } 13: } Our original AddName method: 1: private static string AddName(string theName) 2: { 3: return ExecuteGreetingFunc<string>(theGreetingService => theGreetingService.AddName(theName)); 4: } Our new AddName method: 1: private static int AddName(string firstName, string lastName) 2: { 3: return ExecuteGreetingFunc<int>(theGreetingService => theGreetingService.AddName(firstName, lastName)); 4: } Let’s change the AddName method, just a little bit more for this example and have it take the greeting service as a parameter. 1: private static int AddName(IGreeting greetingService, string firstName, string lastName) 2: { 3: return greetingService.AddName(firstName, lastName); 4: } The new signature of AddName using the Func delegate is now Func<IGreeting, string, string, int>, which can’t be used with ExecuteGreetingFunc as is because it expects Func<IGreeting, TResult>.  Somehow we have to eliminate the two string parameters before we can use this with our existing method.  This is where we need to adapt AddName to match what ExecuteGreetingFunc expects, and we’ll do so in the following progression. 1: Func<IGreeting, string, string, int> -> Func<IGreeting, string, int> 2: Func<IGreeting, string, int> -> Func<IGreeting, int>   For the first step, we’ll create a method using the lambda syntax that will “eliminate” the last name parameter: 1: string lastNameToAdd = "Smith"; 2: //Func<IGreeting, string, string, int> -> Func<IGreeting, string, int> 3: Func<IGreeting, string, int> addName = (greetingService, firstName) => AddName(greetingService, firstName, lastNameToAdd); The new addName method gets us one step close to the signature we need.  Let’s say we’re going to call this in a loop to add several names, we’ll take the final step from Func<IGreeting, string, int> -> Func<IGreeting, int> in line as a lambda passed to ExecuteGreetingFunc like so: 1: List<string> firstNames = new List<string>() { "Bob", "John" }; 2: int aID; 3: foreach (string firstName in firstNames) 4: { 5: //Func<IGreeting, string, int> -> Func<IGreeting, int> 6: aID = ExecuteGreetingFunc<int>(greetingService => addName(greetingService, firstName)); 7: Console.WriteLine(GetGreeting(aID)); 8: } If for some reason you needed to break out the lambda on line 6 you could replace it with 1: aID = ExecuteGreetingFunc<int>(ApplyAddName(addName, firstName)); and use this method: 1: private static Func<IGreeting, int> ApplyAddName(Func<IGreeting, string, int> addName, string lastName) 2: { 3: return greetingService => addName(greetingService, lastName); 4: } Splitting out a lambda into its own method is useful both in this style of coding as well as LINQ queries to improve the debugging experience.  It is not strictly necessary to break apart the steps & functions as was shown above; the lambda in line 6 (of the foreach example) could include both the last name and first name instead of being composed of two functions.  The process demonstrated above is one of partially applying functions, this could have also been done with Currying (also see Dustin Campbell’s excellent post on Currying for the canonical curried add example).  Matthew Podwysocki also has some good posts explaining both Currying and partial application and a follow up post that further clarifies the difference between Currying and partial application.  In either technique the ultimate goal is to reduce the number of parameters passed to a function.  Currying makes it a single parameter passed at each step, where partial application allows one to use multiple parameters at a time as we’ve done here.  This technique isn’t for everyone or every problem, but can be extremely handy when you need to adapt a call to something you don’t control.

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• A Reusable Builder Class for Ruby Testing

  - by Liam McLennan

  My last post was about a class for building test data objects in C#. This post describes the same tool, but implemented in Ruby. The C# version was written first but I originally came up with the solution in my head using Ruby, and then I translated it to C#. The Ruby version was easier to write and is easier to use thanks to Ruby’s dynamic nature making generics unnecessary.  Here are my example domain classes: class Person attr_accessor :name, :age def initialize(name, age) @name = name @age = age end end class Property attr_accessor :street, :manager def initialize(street, manager) @street = street @manager = manager end end and the test class showing what the builder does: class Test_Builder < Test::Unit::TestCase def setup @build = Builder.new @build.configure({ Property => lambda { Property.new '127 Creek St', @build.a(Person) }, Person => lambda { Person.new 'Liam', 26 } }) end def test_create assert_not_nil @build end def test_can_get_a_person @person = @build.a(Person) assert_not_nil @person assert_equal 'Liam', @person.name assert_equal 26, @person.age end def test_can_get_a_modified_person @person = @build.a Person do |person| person.age = 999 end assert_not_nil @person assert_equal 'Liam', @person.name assert_equal 999, @person.age end def test_can_get_a_different_type_that_depends_on_a_type_that_has_not_been_configured_yet @my_place = @build.a(Property) assert_not_nil @my_place assert_equal '127 Creek St', @my_place.street assert_equal @build.a(Person).name, @my_place.manager.name end end Finally, the implementation of Builder: class Builder # defaults is a hash of Class => creation lambda def configure defaults @defaults = defaults end def a(klass) temp = @defaults[klass].call() yield temp if block_given? temp end end

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• We'll be at QCon San Francisco!

  - by Carlos Chang

  Oracle Technology Network is a Platinum sponsor at QCon San Francisco. Don’t miss these great developer focused sessions: Shay Shmeltzer - How we simplified Web, Mobile and Cloud development for our own developers? - the Oracle Story Over the past several years, Oracle has beendeveloping a new set of enterprise applications in what is probably one of the largest Java based development project in the world. How do you take 3000 developers and make them productive? How do you insure the delivery of cutting edge UIs for both Mobile and Web channels? How do you enable Cloud based development and deployment? Come and learn how we did it at Oracle, and see how the same technologies and methodologies can apply to your development efforts. Dan Smith - Project Lambda in Java 8 Java SE 8 will include major enhancements to the Java Programming Language and its core libraries.  This suite of new features, known as Project Lambda in the OpenJDK community, includes lambda expressions, default methods, and parallel collections (and much more!).  The result will be a next-generation Java programming experience with more flexibility and better abstractions.   This talk will introduce the new Java features and offer a behind-the-scenes view of how they evolved and why they work the way that they do. Arun Gupta - JSR 356: Building HTML5 WebSocket Applications in Java The family of HTML5 technologies has pushed the pendulum away from rich client technologies and toward ever-more-capable Web clients running on today’s browsers. In particular, WebSocket brings new opportunities for efficient peer-to-peer communication, providing the basis for a new generation of interactive and “live” Web applications. This session examines the efforts under way to support WebSocket in the Java programming model, from its base-level integration in the Java Servlet and Java EE containers to a new, easy-to-use API and toolset that are destined to become part of the standard Java platform. The complete conference schedule is here: http://qconsf.com/sf2012/schedule/wednesday.jsp But wait, there’s more! At the Oracle booth, we’ll also be covering: Oracle ADF Mobile Oracle Developer Cloud Service Oracle ADF Essentials NetBeans Project Easel Hope to see you there! 

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• Languages with a clear distinction between subroutines that are purely functional, mutating, state-changing, etc?

  - by CPX

  Lately I've become more and more frustrated that in most modern programming languages I've worked with (C/C++, C#, F#, Ruby, Python, JS and more) there is very little, if any, language support for determining what a subroutine will actually do. Consider the following simple pseudo-code: var x = DoSomethingWith(y); How do I determine what the call to DoSomethingWith(y) will actually do? Will it mutate y, or will it return a copy of y? Does it depend on global or local state, or is it only dependent on y? Will it change the global or local state? How does closure affect the outcome of the call? In all languages I've encountered, almost none of these questions can be answered by merely looking at the signature of the subroutine, and there is almost never any compile-time or run-time support either. Usually, the only way is to put your trust in the author of the API, and hope that the documentation and/or naming conventions reveal what the subroutine will actually do. My question is this: Does there exist any languages today that make symbolic distinctions between these types of scenarios, and places compile-time constraints on what code you can actually write? (There is of course some support for this in most modern languages, such as different levels of scope and closure, the separation between static and instance code, lambda functions, et cetera. But too often these seem to come into conflict with each other. For instance, a lambda function will usually either be purely functional, and simply return a value based on input parameters, or mutate the input parameters in some way. But it is usually possible to access static variables from a lambda function, which in turn can give you access to instance variables, and then it all breaks apart.)

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• Scheme Formatting Help

  - by Logan

  I've been working on a project for school that takes functions from a class file and turns them into object/classes. The assignment is all about object oriented programming in scheme. My problem however is that my code doesn't format right. The output it gives me whenever I give it a file to pass in wraps the methods of the class in a list, making it so that the class never really gets declared. I can't for the life of me figure out how to get the parenthesis wrapping the method list to remove. I would really appreciate any help. Below is the code and the class file. ;;;; PART1 --- A super-easy set of classes. Just models points and lines. Tests all of the ;; basics of class behavior without touching on anything particularly complex. (class pointInstance (parent:) (constructor_args:) (ivars: (myx 1) (myy 2)) (methods: (getx () myx) (gety () myy) (setx (x) (set! myx x)) (show () (begin (display "[") (display myx) (display ",") (display myy) (display "]"))) )) (require (lib "trace.ss")) ;; Continue reading until you hit the end of the file, all the while ;; building a list with the contents (define load-file (lambda (port) (let ((rec (read port))) (if (eof-object? rec) '() (cons rec (load-file port)))))) ;; Open a port based on a file name using open-input-file (define (load fname) (let ((fport (open-input-file fname))) (load-file fport))) ;(define lis (load "C:\\Users\\Logan\\Desktop\\simpletest.txt")) ;(define lis (load "C:\\Users\\Logan\\Desktop\\complextest.txt")) (define lis (load "C:\\Users\\Logan\\Desktop\\pointinstance.txt")) ;(display (cdaddr (cdddar lis))) (define makeMethodList (lambda (listToMake retList) ;(display listToMake) (cond [(null? listToMake) retList ;(display "The list passed in to parse was null") ] [else (makeMethodList (cdr listToMake) (append retList (list (getMethodLine listToMake)))) ] ) )) ;(trace makeMethodList) ;this works provided you just pass in the function line (define getMethodLine (lambda (functionList) `((eq? (car msg) ,(caar functionList)) ,(caddar functionList)))) (define load-classes (lambda paramList (cond [(null? paramList) (display "Your parameters are null, man.")] [(null? (car paramList))(display "Done creating class definitions.")] [(not (null? (car paramList))) (begin (let* ((className (cadaar paramList)) (classInstanceVars (cdaddr (cddaar paramList))) (classMethodList (cdr (cadddr (cddaar paramList)))) (desiredMethodList (makeMethodList classMethodList '())) ) ;(display "Classname: ") ;(display className) ;(newline)(newline) ;(display "Class Instance Vars: ") ;(display classInstanceVars) ;(newline)(newline) ;(display "Class Method List: ") ;(display classMethodList) ;(newline) ;(display "Desired Method List: ") ;(display desiredMethodList)) ;(newline)(newline) ;---------------------------------------------------- ;do not delete the below code!` `(define ,className (let ,classInstanceVars (lambda msg ;return the function list here (cond ,(makeMethodList classMethodList '()))) )) ;--------------------------------------------------- ))] ) )) (load-classes lis) ;(load-classes lis) ;(load-classes-helper lis) ;(load-classes "simpletest.txt") ;(load-classes "complextest.txt") ;method list ;(display (cdr (cadddr (cddaar <class>))))

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• request parameter is taking null value in servlets

  - by Dusk

  Hi, I want to know how can I get the value of the request parameters "j_username" and "j_password"? After successfully login using form based authentication, I want my servlet to get the value of parameters "j_username" and "j_password", but I'm getting null as the value in both parameters. Could anyone please tell me how can I get the actual value of both paramters? Servlets class : package foo; import javax.servlet.http.*; import javax.servlet.*; public class RequestHandler extends HttpServlet { public void doGet(HttpServletRequest request, HttpServletResponse response) { try { String user = request.getParameter("j_username"); String password = request.getParameter("j_password"); response.getWriter().println(user+" "+password); } catch(Exception e) { e.printStackTrace(); } } } output: null null

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• Help with iphone dev - beyond bounds error

  - by dusk

  I'm just learning iphone development, so please forgive me for what is probably a beginner error. I've searched around and haven't found anything specific to my problem, so hopefully it is an easy fix. The book has examples of building a table from data hard coded via an array. Unfortunately it never really tells you how to get data from a URL, so I've had to look that up and that is where my problems show up. When I debug in xcode, it seems like the count is correct, so I don't understand why it is going out of bounds? This is the error message: 2010-05-03 12:50:42.705 Simple Table[3310:20b] *** Terminating app due to uncaught exception 'NSRangeException', reason: '*** -[NSCFArray objectAtIndex:]: index (1) beyond bounds (0)' My URL returns the following string: first,second,third,fourth And here is the iphone code with the book's working example commented out #import "Simple_TableViewController.h" @implementation Simple_TableViewController @synthesize listData; - (void)viewDidLoad { /* //working code from book NSArray *array = [[NSArray alloc] initWithObjects:@"Sleepy", @"Sneezy", @"Bashful", @"Bashful", @"Happy", @"Doc", @"Grumpy", @"Thorin", @"Dorin", @"Norin", @"Ori", @"Balin", @"Dwalin", @"Fili", @"Kili", @"Oin", @"Gloin", @"Bifur", @"Bofur", @"Bombur", nil]; self.listData = array; [array release]; */ //code from interwebz that crashes NSString *urlstr = [[NSString alloc] initWithFormat:@"http://www.mysite.com/folder/iphone-test.php"]; NSURL *url = [[NSURL alloc] initWithString:urlstr]; NSString *ans = [NSString stringWithContentsOfURL:url]; NSArray *listItems = [ans componentsSeparatedByString:@","]; self.listData = listItems; [urlstr release]; [url release]; [ans release]; [listItems release]; [super viewDidLoad]; } - (void)didReceiveMemoryWarning { // Releases the view if it doesn't have a superview. [super didReceiveMemoryWarning]; // Release any cached data, images, etc that aren't in use. } - (void)viewDidUnload { // Release any retained subviews of the main view. // e.g. self.myOutlet = nil; self.listData = nil; [super viewDidUnload]; } - (void)dealloc { [listData release]; [super dealloc]; } #pragma mark - #pragma mark Table View Data Source Methods - (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section { return [self.listData count]; } - (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath { static NSString *SimpleTableIdentifier = @"SimpleTableIdentifier"; UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:SimpleTableIdentifier]; if (cell == nil) { cell = [[[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:SimpleTableIdentifier] autorelease]; } NSUInteger row = [indexPath row]; cell.textLabel.text = [listData objectAtIndex:row]; return cell; } @end

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• How to set the email protocol in JavaMail

  - by Dusk

  If I need to get inbox messages by passing request from servlets to javamail API , how can I know the protocol in which to retrieve inbox messages? Do I have to state the protocol in request URL? I've already checked in gmail, where they haven't stated any protocol, then How can I get inbox messages based on particular protocol like: POP3 or IMAP

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• How to configure tomcat 6.0 for mysql

  - by Dusk

  I'm using Tomcat 6.0, and I want to know how can I configure Tomcat's server.xml file to connect to mysql database, and enable form based authentication in java. I'm currently using mysql 5.1, and I've already downloaded mysql connector jar file, and put in lib directory of Tomcat.

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• how to know the protocol from servlets

  - by Dusk

  If I need to get inbox messages by passing request from servlets to javamail API , how can I know the protocol in which to retrieve inbox messages? Do I have to state the protocol in request URL? I've already checked in gmail, where they haven't stated any protocol, then How can I get inbox messages based on particular protocol like: POP3 or IMAP

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• How to get login password in servlets

  - by Dusk

  I've successfully implemented form based authentication, and now I want to get the username and password to initialize session object in javamail from servlets. How can I do that? I can getlogin username by using method request.getRemoteUser(), but I don't know how to get the password. If I create any session object like: authentication = new PasswordAuthentication(user,password); Properties props = new Properties(); props.put("mail.host", "localhost"); props.put("mail.debug",true); props.put("mail.store.protocol", "pop3"); props.put("mail.transport.protocol", "smtp"); Session session = Session.getInstance(props, this); then how can I get inbox messages from mail server based upon particular username and password, if I don't pass any password from servlets to PasswordAuthentication object?

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• ClassNotFoundException com.mysql.jdbc.Driver

  - by Dusk

  This question might have asked here number of times . After doing some google search for the above error and doing some update, I can't understand why I'm still getting that error. I've already put my driver-- mysql-connector-java-5.1.5-bin in the classpath: Java_Home\jre\lib\ Java_Home\jre\lib\ext\ Java_Home\lib and the code which I'm using to connect to mysql database is: try{ Class.forName("com.mysql.jdbc.Driver"); Connection con=DriverManager.getConnection("jdbc:mysql://localhost:3306/mail","root",""); Statement stmt = con.createStatement(); ResultSet rs = stmt.executeQuery("select message_body from deadletter"); String dbtime; while (rs.next()) { dbtime = rs.getString(1); System.out.println(dbtime); } con.close(); } catch (SQLException e) { System.out.println("Connection Failed! Check output console"); e.printStackTrace(); } } and the complete stacktrace of the above exception is: java.lang.ClassNotFoundException: com.mysql.jdbc:Driver at java.net.URLClassLoader$1.run(URLClassLoader.java:200) at java.security.AccessController.doPrivileged(Native Method) at java.net.URLClassLoader.findClass(URLClassLoader.java:307) at java.lang.ClassLoader.loadClass(ClassLoader.java:307) at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:301) at java.lang.ClassLoader.loadClass(ClassLoader.java:252) at java.lang.ClassLoader.loadClassInternal(ClassLoader.java:320) at java.lang.Class.forName0(Native Method) at java.lang.Class.forName(Class.java:169) at mail.main(mail.java:114) Now, what's wrong I'm doing here?

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• Arithmetic operator confusion

  - by Dusk

  Why I'm getting two different values while using the arithmetic operators for the same value of variables. I've just altered little bit my second program, which is resulted in giving me the different output. Could anyone please tell me why? int number=113; int rot=0; rot=number%10; rot*=100+number/10; System.out.println(rot);//333 int number=113; int rot=0; rot=number%10; rot=rot*100+number/10; System.out.println(rot);//311

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• Confusion in RegExp Reluctant quantifier? Java

  - by Dusk

  Hi, Could anyone please tell me the reason of getting an output as: ab for the following RegExp code using Relcutant quantifier? Pattern p = Pattern.compile("abc*?"); Matcher m = p.matcher("abcfoo"); while(m.find()) System.out.println(m.group()); // ab and getting empty indices for the following code? Pattern p = Pattern.compile(".*?"); Matcher m = p.matcher("abcfoo"); while(m.find()) System.out.println(m.group());

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• How to check a bool setting in my iphone app

  - by dusk

  I have a setting in Root.plist with Key = 'latestNews' of type PSToggleSwitchSpecifier and DefaultValue as a boolean that is checked. If I understand that correctly, it should = YES when I pull it in to my code. I'm trying to check that value and set an int var to pass it to my php script. What is happening is that my boolean is either nil or NO and then my int var = 0. What am I doing wrong? int latestFlag; NSUserDefaults *prefs = [NSUserDefaults standardUserDefaults]; BOOL latestNews = [prefs boolForKey:@"latestNews"]; if (latestNews) latestFlag = 1; else latestFlag = 0; NSString *urlstr = [[NSString alloc] initWithFormat:@"http://www.mysite.com/folder/iphone-test.php?latest=%d", latestFlag]; NSURL *url = [[NSURL alloc] initWithString:urlstr]; //these are auto-released NSString *ans = [NSString stringWithContentsOfURL:url]; NSArray *listItems = [ans componentsSeparatedByString:@","]; self.listData = listItems; [urlstr release]; [url release];

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• Confusion in JavaScript RegExp ? Quantifier

  - by Dusk

  Hi, May I know the reason of getting the output of the following code as: 1,10,10? Why not it is as: 10, 10? <script type="text/javascript"> var str="1, 100 or 1000?"; var patt1=/10?/g; document.write(str.match(patt1)); </script>

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• How to validate username using Javascript?

  - by Dusk

  Hi, I want to know how can I validate using Javascript that if user has entered any username at the time of creating an account is already present in database and ask user to type any other username?

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• How do I defer execution of some Ruby code until later and run it on demand in this scenario?

  - by Kyle Kaitan

  I've got some code that looks like the following. First, there's a simple Parser class for parsing command-line arguments with options. class Parser def initialize(&b); ...; end # Create new parser. def parse(args = ARGV); ...; end # Consume command-line args. def opt(...); ...; end # Declare supported option. def die(...); ...; end # Validation handler. end Then I have my own Parsers module which holds some metadata about parsers that I want to track. module Parsers ParserMap = {} def self.make_parser(kind, desc, &b) b ||= lambda {} module_eval { ParserMap[kind] = {:desc => "", :validation => lambda {} } ParserMap[kind][:desc] = desc # Create new parser identified by `<Kind>Parser`. Making a Parser is very # expensive, so we defer its creation until it's actually needed later # by wrapping it in a lambda and calling it when we actually need it. const_set(name_for_parser(kind), lambda { Parser.new(&b) }) } end # ... end Now when you want to add a new parser, you can call make_parser like so: make_parser :db, "login to database" do # Options that this parser knows how to parse. opt :verbose, "be verbose with output messages" opt :uid, "user id" opt :pwd, "password" end Cool. But there's a problem. We want to optionally associate validation with each parser, so that we can write something like: validation = lambda { |parser, opts| parser.die unless opts[:uid] && opts[:pwd] # Must provide login. } The interface contract with Parser says that we can't do any validation until after Parser#parse has been called. So, we want to do the following: Associate an optional block with every Parser we make with make_parser. We also want to be able to run this block, ideally as a new method called Parser#validate. But any on-demand method is equally suitable. How do we do that?

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• Using Lambdas for return values in Rhino.Mocks

  - by PSteele

  In a recent StackOverflow question, someone showed some sample code they’d like to be able to use.  The particular syntax they used isn’t supported by Rhino.Mocks, but it was an interesting idea that I thought could be easily implemented with an extension method. Background When stubbing a method return value, Rhino.Mocks supports the following syntax: dependency.Stub(s => s.GetSomething()).Return(new Order()); The method signature is generic and therefore you get compile-time type checking that the object you’re returning matches the return value defined by the “GetSomething” method. You could also have Rhino.Mocks execute arbitrary code using the “Do” method: dependency.Stub(s => s.GetSomething()).Do((Func<Order>) (() => new Order())); This requires the cast though.  It works, but isn’t as clean as the original poster wanted.  They showed a simple example of something they’d like to see: dependency.Stub(s => s.GetSomething()).Return(() => new Order()); Very clean, simple and no casting required.  While Rhino.Mocks doesn’t support this syntax, it’s easy to add it via an extension method. The Rhino.Mocks “Stub” method returns an IMethodOptions<T>.  We just need to accept a Func<T> and use that as the return value.  At first, this would seem straightforward: public static IMethodOptions<T> Return<T>(this IMethodOptions<T> opts, Func<T> factory) { opts.Return(factory()); return opts; } And this would work and would provide the syntax the user was looking for.  But the problem with this is that you loose the late-bound semantics of a lambda.  The Func<T> is executed immediately and stored as the return value.  At the point you’re setting up your mocks and stubs (the “Arrange” part of “Arrange, Act, Assert”), you may not want the lambda executing – you probably want it delayed until the method is actually executed and Rhino.Mocks plugs in your return value. So let’s make a few small tweaks: public static IMethodOptions<T> Return<T>(this IMethodOptions<T> opts, Func<T> factory) { opts.Return(default(T)); // required for Rhino.Mocks on non-void methods opts.WhenCalled(mi => mi.ReturnValue = factory()); return opts; } As you can see, we still need to set up some kind of return value or Rhino.Mocks will complain as soon as it intercepts a call to our stubbed method.  We use the “WhenCalled” method to set the return value equal to the execution of our lambda.  This gives us the delayed execution we’re looking for and a nice syntax for lambda-based return values in Rhino.Mocks. Technorati Tags: .NET,Rhino.Mocks,Mocking,Extension Methods

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• Help with dynamic-wind and call/cc

  - by josh

  I am having some trouble understanding the behavior of the following Scheme program: (define c (dynamic-wind (lambda () (display 'IN)(newline)) (lambda () (call/cc (lambda (k) (display 'X)(newline) k))) (lambda () (display 'OUT)(newline)))) As I understand, c will be bound to the continution created right before "(display 'X)". But using c seems to modify itself! The define above prints (as I expected) IN, X and OUT: IN X OUT And it is a procedure: #;2> c #<procedure (a9869 . results1678)> Now, I would expect that when it is called again, X would be printed, and it is not! #;3> (c) IN OUT And now c is not a procedure anymore, and a second invokation of c won't work! #;4> c ;; the REPL doesn't answer this, so there are no values returned #;5> (c) Error: call of non-procedure: #<unspecified> Call history: <syntax> (c) <eval> (c) <-- I was expecting that each invokation to (c) would do the same thing -- print IN, X, and OUT. What am I missing?

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• CarrierWave and nested forms saving empty image object if photo :title is included in form

  - by Wasabi Developer

  I'm after some advice in regards to handling nested form data and I would be ever so grateful for any insights. The trouble is I'm not 100% sure why I require the following code in my model accepts_nested_attributes_for :holiday_image, allow_destroy: true, :reject_if => lambda { |a| a[:title].blank? } If I don't understand why I require to tact on on my accepts_nested_attributes_for association: :reject_if => lambda { |a| a[:title].blank? } If I remove this :reject_if lambda, it will save a blank holiday photo object in the database. I presume because it takes the :title field from the form as an empty string? I guess my question is, am I doing this right or is there a better way of this this within nested forms if I want to extend my HolidayImage model to include more strings like description, notes? Sorry If I can't be more succinct. My simple holiday app. # holiday.rb class Holiday < ActiveRecord::Base has_many :holiday_image accepts_nested_attributes_for :holiday_image, allow_destroy: true, :reject_if => lambda { |a| a[:title].blank? } attr_accessible :name, :content, :holiday_image_attributes end I'm using CarrierWave for image uploads. # holiday_image.rb class HolidayImage < ActiveRecord::Base belongs_to :holiday attr_accessible :holiday_id, :image, :title mount_uploader :image, ImageUploader end Inside my _form partial there is a field_for block <h3>Photo gallery</h3> <%= f.fields_for :holiday_image do |holiday_image| %> <% if holiday_image.object.new_record? %> <%= holiday_image.label :title, "Image Title" %> <%= holiday_image.text_field :title %> <%= holiday_image.file_field :image %> <% else %> Title: <%= holiday_image.object.title %> <%= image_tag(holiday_image.object.image.url(:thumb)) %> Tick to delete: <%= holiday_image.check_box :_destroy %> <% end %> Thanks again for your patience.

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• do the Python libraries have a natural dependence on the global namespace?

  - by msw

  I first ran into this when trying to determine the relative performance of two generators: t = timeit.repeat('g.get()', setup='g = my_generator()') So I dug into the timeit module and found that the setup and statement are evaluated with their own private, initially empty namespaces so naturally the binding of g never becomes accessible to the g.get() statement. The obvious solution is to wrap them into a class, thus adding to the global namespace. I bumped into this again when attempting, in another project, to use the multiprocessing module to divide a task among workers. I even bundled everything nicely into a class but unfortunately the call pool.apply_async(runmc, arg) fails with a PicklingError because buried inside the work object that runmc instantiates is (effectively) an assignment: self.predicate = lambda x, y: x > y so the whole object can't be (understandably) pickled and whereas: def foo(x, y): return x > y pickle.dumps(foo) is fine, the sequence bar = lambda x, y: x > y yields True from callable(bar) and from type(bar), but it Can't pickle <function <lambda> at 0xb759b764>: it's not found as __main__.<lambda>. I've given only code fragments because I can easily fix these cases by merely pulling them out into module or object level defs. The bug here appears to be in my understanding of the semantics of namespace use in general. If the nature of the language requires that I create more def statements I'll happily do so; I fear that I'm missing an essential concept though. Why is there such a strong reliance on the global namespace? Or, what am I failing to understand? Namespaces are one honking great idea -- let's do more of those!

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• using Python reduce over a list of pairs

  - by user248237

  I'm trying to pair together a bunch of elements in a list to create a final object, in a way that's analogous to making a sum of objects. I'm trying to use a simple variation on reduce where you consider a list of pairs rather than a flat list to do this. I want to do something along the lines of: nums = [1, 2, 3] reduce(lambda x, y: x + y, nums) except I'd like to add additional information to the sum that is specific to each element in the list of numbers nums. For example for each pair (a,b) in the list, run the sum as (a+b): nums = [(1, 0), (2, 5), (3, 10)] reduce(lambda x, y: (x[0]+x[1]) + (y[0]+y[1]), nums) This does not work: >>> reduce(lambda x, y: (x[0]+x[1]) + (y[0]+y[1]), nums) Traceback (most recent call last): File "<stdin>", line 1, in <module> File "<stdin>", line 1, in <lambda> TypeError: 'int' object is unsubscriptable Why does it not work? I know I can encode nums as a flat list - that is not the point - I just want to be able to create a reduce operation that can iterate over a list of pairs, or over two lists of the same length simultaneously and pool information from both lists. thanks.

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• Scheme Function to reverse elements of list of 2-list

  - by sudhirc

  This is an exercise from EOPL. Procedure (invert lst) takes lst which is a list of 2-lists and returns a list with each 2-list reversed. (define invert (lambda (lst) (cond((null? lst ) '()) ((= 2 (rtn-len (car lst))) ( cons(swap-elem (car lst)) (invert (cdr lst)))) ("List is not a 2-List")))) ;; Auxiliry Procedure swap-elements of 2 element list (define swap-elem (lambda (lst) (cons (car (cdr lst)) (car lst)))) ;; returns lengh of the list by calling (define rtn-len (lambda (lst) (calc-len lst 0))) ;; calculate length of the list (define calc-len (lambda (lst n) (if (null? lst) n (calc-len (cdr lst) (+ n 1))))) This seems to work however looks very verbose. Can this be shortened or written in more elegant way ? How I can halt the processing in any of the individual element is not a 2-list? At the moment execution proceed to next member and replacing current member with "List is not a 2-List" if current member is not a 2-list.

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