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• How would you solve this graph theory handshake problem in python?

  - by Zachary Burt

  I graduated college last year with a degree in Psychology, but I also took a lot of math for fun. I recently got the book "Introductory Graph Theory" by Gary Chartrand to brush up on my math and have some fun. Here is an exercise from the book that I'm finding particularly befuddling: Suppose you and your husband attended a party with three other married couples. Several handshakes took place. No one shook hands with himself (or herself) or with his (or her) spouse, and no one shook hands with the same person more than once. After all the handshaking was completed, suppose you asked each person, including your husband, how many hands he or she had shaken. Each person gave a different answer. a) How many hands did you shake? b) How many hands did your husband shake? Now, I've been reasoning about this for a while, and trying to draw sample graphs that could illustrate a solution, but I'm coming up empty-handed. My logic is this: there are 8 different vertices in the graph, and 7 of them have different degrees. The values for the degrees must therefore be 0, 1, 2, 3, 4, 5, 6, and x. The # of degrees for one married couple is (0, 6). Since all graphs have an even number of odd vertices, x must be either 5, 3, or 1. What's your solution to this problem? And, if you could solve it in python, how would you do it? (python is fun.) Cheers.

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• How would you solve this graph theory handshake problem in python?

  - by Zachary Burt

  I graduated college last year with a degree in Psychology, but I also took a lot of math for fun. I recently got the book "Introductory Graph Theory" by Gary Chartrand to brush up on my math and have some fun. Here is an exercise from the book that I'm finding particularly befuddling: Suppose you and your husband attended a party with three other married couples. Several handshakes took place. No one shook hands with himself (or herself) or with his (or her) spouse, and no one shook hands with the same person more than once. After all the handshaking was completed, suppose you asked each person, including your husband, how many hands he or she had shaken. Each person gave a different answer. a) How many hands did you shake? b) How many hands did your husband shake? Now, I've been reasoning about this for a while, and trying to draw sample graphs that could illustrate a solution, but I'm coming up empty-handed. My logic is this: there are 8 different vertices in the graph, and 7 of them have different degrees. The values for the degrees must therefore be 0, 1, 2, 3, 4, 5, 6, and x. The # of degrees for one married couple is (0, 6). Since all graphs have an even number of odd vertices, x must be either 5, 3, or 1. What's your solution to this problem? And, if you could solve it in python, how would you do it? (python is fun.) Cheers.

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• Max Value of a Multiway Tree in OCaml

  - by Trigork

  I'm an IT Student and kind of a newbie to OCaml Recently, studying for an exam I found this exercise. Given: type 'a tree = Tree of 'a * 'a tree list Define a function mtree : 'a tree -'a, that returns the greatest value of all the nodes in a multiway tree, following the usual order relation in OCaml (<=) I've come to do something like this below, which, of course, is not working. let rec mtree (Tree (r, sub)) = let max_node (Tree(a, l1)) (Tree(b, l2)) = if a >= b then (Tree(a, l1)) else (Tree(b, l2)) in List.fold_left max_node r sub;; After reading an answer to this I'm posting the fixed code. let rec mtree (Tree(r,sub)) = let max_node (Tree(a, l1)) (Tree(b, l2)) = if a >= b then a else b in List.fold_left (max_node) r (List.map mtree sub);; The idea is the same, fold the list comparing the nodes making use of my local function to do so and travel through the tree by calling the function itself over the nodes lists of the consecutive levels. Is still not working, though. Now complains about max_node in the fold_left part. Error: This expression has type 'a tree -> 'a tree -> 'a but an expression was expected of type 'a tree -> 'a tree -> 'a tree And here I'm definitely lost because I can't see why does it expects to return an 'a tree

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• Jar not found when executing class

  - by Simon

  Hi there, I'm working through the ANTLR book and there are many examples that should be easy to compile using the command line. Some information to get te problem: antlr-3.2.jar contains the ANTLR classes. I added the antlr-3.2.jar to the CLASSPATH environment variable (Windows 7) and when compiling the classes with javac everything works fine. This is what i execute to compile my program: javac Test.java ExprLexer.java ExprParser.java Test.java contains my main()-method whereas ExprLexer and ExprParser are generated by ANTLR. All three classes use classes contained in the antlr-3.2.jar. But so far so good. As I just said, compiling works fine. It's when I try to execute the Test.class that I get trouble. This is what I type: java -cp ./ Test When executing this, the interpreter tells me that he can't find the ANTLR-classes contained in the antlr-3.2.jar, altough I added an entry in the CLASSPATH variable. E:\simone\Programmierung\Language Processing Tools\ANTLR\Book Samples and Exercises\Exercise\1\output\Test.java Exception in thread "main" java.lang.NoClassDefFoundError: org/antlr/runtime/Cha rStream Caused by: java.lang.ClassNotFoundException: org.antlr.runtime.CharStream at java.net.URLClassLoader$1.run(URLClassLoader.java:202) at java.security.AccessController.doPrivileged(Native Method) at java.net.URLClassLoader.findClass(URLClassLoader.java:190) at java.lang.ClassLoader.loadClass(ClassLoader.java:307) at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:301) at java.lang.ClassLoader.loadClass(ClassLoader.java:248) Could not find the main class: Test. Program will exit. I'm using Windows 7 and Java 1.6_20. Can someone tell what is going on? Why will the interpreter not look in the jar-Archive I specified in the CLASSPATH? I found some kind of workaroud. I copied the antlr-3.2.jar into the directory where the Test.class is located and then executed: java -cp ./;antlr-3.2.jar Test This worked out. But I don't want to type the jar-Archive everytime I execute my test programs. Is there a possibility to tell the interpreter that he should automatically look into the archive?

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• Double type returns -1.#IND/NaN error when calculating pi iteratively

  - by Draak

  I am working through a problem for my MCTS certification. The program has to calculate pi until the user presses a key, at which point the thread is aborted, the result returned to the main thread and printed in the console. Simple enough, right? This exercise is really meant to be about threading, but I'm running into another problem. The procedure that calculates pi returns -1.#IND. I've read some of the material on the web about this error, but I'm still not sure how to fix it. When I change double to Decimal type, I unsurprisingly get Overflow Exception very quickly. So, the question is how do I store the numbers correctly? Do I have to create a class to somehow store parts of the number when it gets too big to be contained in a Decimal? Class PiCalculator Dim a As Double = 1 Dim b As Double = 1 / Math.Sqrt(2) Dim t As Double = 1 / 4 Dim p As Double = 1 Dim pi As Double Dim callback As DelegateResult Sub New(ByVal _callback As DelegateResult) callback = _callback End Sub Sub Calculate() Try Do While True Dim a1 = (a + b) / 2 Dim b1 = Math.Sqrt(a * b) Dim t1 = t - p * (a - a1) ^ 2 Dim p1 = 2 * p a = a1 b = b1 t = t1 p = p1 pi = ((a + b) ^ 2) / (4 * t) Loop Catch ex As ThreadAbortException Finally callback(pi) End Try End Sub End Class

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• Renaming column in Android sqlite database results in error

  - by Apophenia Overload

  I've been modifying the Notepad tutorial for Android very subtly- all I did was rename the column from title to name: Before: public static final String KEY_TITLE = "title"; ... private static final String DATABASE_CREATE = "create table notes (_id integer primary key autoincrement, " + "title text not null, body text not null);"; After: public static final String KEY_TITLE = "name"; ... private static final String DATABASE_CREATE = "create table notes (_id integer primary key autoincrement, " + "name text not null, body text not null);"; However, it always results in this: 06-10 03:29:38.421: ERROR/AndroidRuntime(344): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.android.demo.notepad1/com.android.demo.notepad1.Notepadv1}: android.database.sqlite.SQLiteException: no such column: name: , while compiling: SELECT _id, name, body FROM notes ... 06-10 03:29:38.421: ERROR/AndroidRuntime(344): Caused by: android.database.sqlite.SQLiteException: no such column: name: , while compiling: SELECT _id, name, body FROM notes Am I failing to rename something? All I am modifying is the Exercise 1 Solution program from the Notepad tutorial.

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• Simple Program Question (TI-84 calculator)

  - by John

  I wrote a program (on my TI-84 calculator) to satisfy the following exercise: Write a program that will print all solutions of the inequality ax + b < c, where a, b, and c are entered by the user. In this program the domain of x will be a set of consecutive integers, where the smallest and largest members of the set will also be entered by the user. (Hint: Use a FOR . . . NEXT loop to test each integer from smallest to largest.) This is the code I have: :Input "A=",A :Input "B=",B :Input "C=",C :Disp "DOMAIN FOR X" :Input "MIN=",D :Input "MAX=",E :For(X,D,E,1) :If AX+B<C :Disp X :End I sort of figured it out by chance; I don't really know how 'If' works inside 'For.' I wanted to have it tell me if there is no solution, though, so I tried: :Input "A=",A :Input "B=",B :Input "C=",C :Disp "DOMAIN FOR X" :Input "MIN=",D :Input "MAX=",E :For(X,D,E,1) :If AX+B<C :Then :Disp X :Else :Disp "NO SOLUTION" :End But this returns the value for "MIN=" Why is this? Can anyone help me understand these work?

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• C#: WebBrowser.Navigated Only Fires when I MessageBox.Show();

  - by tsilb

  I have a WebBrowser control which is being instantiated dynamically from a background STA thread because the parent thread is a BackgroundWorker and has lots of other things to do. The problem is that the Navigated event never fires, unless I pop a MessageBox.Show() in the method that told it to .Navigate(). I shall explain: ThreadStart ts = new ThreadStart(GetLandingPageContent_ChildThread); Thread t = new Thread(ts); t.SetApartmentState(ApartmentState.STA); t.Name = "Mailbox Processor"; t.Start(); protected void GetLandingPageContent_ChildThread() { WebBrowser wb = new WebBrowser(); wb.Navigated += new WebBrowserNavigatedEventHandler(wb_Navigated); wb.Navigate(_url); MessageBox.Show("W00t"); } protected void wb_Navigated(object sender, WebBrowserNavigatedEventArgs e) { WebBrowser wb = (WebBrowser)sender; // Breakpoint HtmlDocument hDoc = wb.Document; } This works fine; but the messagebox will get in the way since this is an automation app. When I remove the MessageBox.Show(), the WebBrowser.Navigated event never fires. I've tried supplanting this line with a Thread.Sleep(), and by suspending the parent thread. Once I get this out of the way, I intend to Suspend the parent thread while the WebBrowser is doing its job and find some way of passing the resulting HTML back to the parent thread so it can continue with further logic. Why does it do this? How can I fix it? If someone can provide me with a way to fetch the content of a web page, fill out some data, and return the content of the page on the other side of the submit button, all against a webserver that doesn't support POST verbs nor passing data via QueryString, I'll also accept that answer as this whole exercise will have been unneccessary.

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• Software development metrics and reporting

  - by David M

  I've had some interesting conversations recently about software development metrics, in particular how they can be used in a reasonably large organisation to help development teams work better. I know there have been Stack Overflow questions about which metrics are good to use - like this one, but my question is more about which metrics are useful to which stakeholders, and at what level of aggregation. As an example, my view is that code coverage is a useful metric in the following ways (and maybe others): For a team's own internal use when combined with other measurements. For facilitating/enabling/mentoring teams, where it might be instructive when considered on a team-by-team basis as a trend (e.g. if team A and B have coverage this month of 75 and 50, I'd be more concerned with team A than B if the previous month they'd had 80 and 40). For senior management when presented as an aggregated statistic across a number of teams or a whole department. But I don't think it's useful for senior management to see this on a team-by-team basis, as this encourages artifical attempts to bolster coverage with tests that merely exercise, rather than test, code. I'm in an organisation with a couple of levels in its management hierarchy, but where the vast majority of managers are technically minded and able (with many still getting their hands dirty). Some of the development teams are leading the way in driving towards agile development practices, but others lag, and there is now a serious mandate from the top for this to be the way the organisation works. A couple of us are starting a programme to encourage this. In this sort of an organisation, what sort of metrics do you think are useful, to whom, why, and at what level of aggregation? I don't want people to feel their performance is being assessed based on a metric that they can artificially influence; at the same time, the senior management are going to want some sort of evidence that progress is being made. What advice or caveats can you provide based on experience in your own organisations? EDIT We are definitely wanting to use metrics as a tool for organisational improvement not as a tool for individual performance measurement.

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• Is there any special tool for interactive GUI development

  - by niko

  Hi, Currently I am preparing exercises about networks and mobile communications for students. I was thinking about creating an interactive user-interface which enables the user to drag&drop predefined elements and then implement a logic based upon element distances etc. An example would be to place two base stations (a predefined element with several properties), set the scale in the interface and then check the signal interferrence in the environment (user-interface). The first part might be too abstract whereas the example might be too specific, but I was wondering whether there already exists any friendly framework or language which enables developers to create interactive interfaces (for teaching/learning purpouses) in short ammount of time. Usually I write applications for PC environment in .NET but in this case it would take too much time to create a specific interface for every exercise. I would appreciate if anyone could suggest any way to create interactive user-interface in short ammount of time. Are there any special programming languages or development tools for this kind of applications or are there any useful frameworks for .NET, Java or any other language to speed up the development of user-interfaces? Thank you!

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• TypeError: coercing to Unicode: need string or buffer, User found

  - by Clemens

  hi, i have to crawl last.fm for users (university exercise). I'm new to python and get following error: Traceback (most recent call last): File "crawler.py", line 23, in <module> for f in user_.get_friends(limit='200'): File "/opt/local/Library/Frameworks/Python.framework/Versions/2.6/lib/python2.6/site-packages/pylast.py", line 2717, in get_friends for node in _collect_nodes(limit, self, "user.getFriends", False): File "/opt/local/Library/Frameworks/Python.framework/Versions/2.6/lib/python2.6/site-packages/pylast.py", line 3409, in _collect_nodes doc = sender._request(method_name, cacheable, params) File "/opt/local/Library/Frameworks/Python.framework/Versions/2.6/lib/python2.6/site-packages/pylast.py", line 969, in _request return _Request(self.network, method_name, params).execute(cacheable) File "/opt/local/Library/Frameworks/Python.framework/Versions/2.6/lib/python2.6/site-packages/pylast.py", line 721, in __init__ self.sign_it() File "/opt/local/Library/Frameworks/Python.framework/Versions/2.6/lib/python2.6/site-packages/pylast.py", line 727, in sign_it self.params['api_sig'] = self._get_signature() File "/opt/local/Library/Frameworks/Python.framework/Versions/2.6/lib/python2.6/site-packages/pylast.py", line 740, in _get_signature string += self.params[name] TypeError: coercing to Unicode: need string or buffer, User found i use the pylast lib for crawling. what i want to do: i want to get a users friends and the friends of the users friends. the error occurs, when i have a for loop in another for loop. here's the code: network = pylast.get_lastfm_network(api_key = API_KEY, api_secret = API_SECRET, username = username, password_hash = password_hash) user = network.get_user("vidarnelson") friends = user.get_friends(limit='200') i = 1 for friend in friends: user_ = network.get_user(friend) print '#%d %s' % (i, friend) i = i + 1 for f in user_.get_friends(limit='200'): print f any advice? thanks in advance. regards!

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• JSONP request using jquery $.getJSON not working on well formed JSON.

  - by Antti

  I'm not sure is it possible now from the url I am trying. Please see this url: http://www.heiaheia.com/voimakaksikko/stats.json It always serves the same padding function "voimakaksikkoStats". It is well formed JSON, but I have not been able to load it from remote server. Does it need some work from the server side or can it be loaded with javascript? I think the problems gotta to have something to with that callback function... JQuery is not requirement, but it would be nice. This (callback=voimakaksikkoStats) returns nothing (firebug - net - response), and alert doesn't fire: $.getJSON("http://www.heiaheia.com/voimakaksikko/stats.json?callback=voimakaksikkoStats", function(data){ alert(data); }) but this (callback=?): $.getJSON("http://www.heiaheia.com/voimakaksikko/stats.json?callback=?", function(data){ alert(data); }) returns: voimakaksikkoStats({"Top5Sports":[],"Top5Tests":{"8":"No-exercise ennuste","1":"Painoindeksi","2":"Vy\u00f6t\u00e4r\u00f6n ymp\u00e4rys","10":"Cooperin testi","4":"Etunojapunnerrus"},"Top5CitiesByTests":[],"Top5CitiesByExercises":[],"ExercisesLogged":0,"Top5CitiesByUsers":[""],"TestsTaken":22,"RegisteredUsers":1}); But I cannot access it... In both examples the alert never fires. Can someone help?

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• Bubble Breaker Game Solver better than greedy?

  - by Gregory

  For a mental exercise I decided to try and solve the bubble breaker game found on many cell phones as well as an example here:Bubble Break Game The random (N,M,C) board consists N rows x M columns with C colors The goal is to get the highest score by picking the sequence of bubble groups that ultimately leads to the highest score A bubble group is 2 or more bubbles of the same color that are adjacent to each other in either x or y direction. Diagonals do not count When a group is picked, the bubbles disappear, any holes are filled with bubbles from above first, ie shift down, then any holes are filled by shifting right A bubble group score = n * (n - 1) where n is the number of bubbles in the bubble group The first algorithm is a simple exhaustive recursive algorithm which explores going through the board row by row and column by column picking bubble groups. Once the bubble group is picked, we create a new board and try to solve that board, recursively descending down Some of the ideas I am using include normalized memoization. Once a board is solved we store the board and the best score in a memoization table. I create a prototype in python which shows a (2,15,5) board takes 8859 boards to solve in about 3 seconds. A (3,15,5) board takes 12,384,726 boards in 50 minutes on a server. The solver rate is ~3k-4k boards/sec and gradually decreases as the memoization search takes longer. Memoization table grows to 5,692,482 boards, and hits 6,713,566 times. What other approaches could yield high scores besides the exhaustive search? I don't seen any obvious way to divide and conquer. But trending towards larger and larger bubbles groups seems to be one approach Thanks to David Locke for posting the paper link which talks above a window solver which uses a constant-depth lookahead heuristic.

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• DrScheme versus mzscheme: treatment of definitions

  - by speciousfool

  One long term project I have is working through all the exercises of SICP. I noticed something a bit odd with the most recent exercise. I am testing a Huffman encoding tree. When I execute the following code in DrScheme I get the expected result: (a d a b b c a) However, if I execute this same code in mzscheme by calling (load "2.67.scm") or by running mzscheme -f 2.67.scm, it reports: symbols: expected symbols as arguments, given: (leaf D 1) My question is: why? Is it because mzscheme and drscheme use different rules for loading program definitions? The program code is below. ;; Define an encoding tree and a sample message ;; Use the decode procedure to decode the message, and give the result. (define (make-leaf symbol weight) (list 'leaf symbol weight)) (define (leaf? object) (eq? (car object) 'leaf)) (define (symbol-leaf x) (cadr x)) (define (weight-leaf x) (caddr x)) (define (make-code-tree left right) (list left right (append (symbols left) (symbols right)) (+ (weight left) (weight right)))) (define (left-branch tree) (car tree)) (define (right-branch tree) (cadr tree)) (define (symbols tree) (if (leaf? tree) (list (symbol-leaf tree)) (caddr tree))) (define (weight tree) (if (leaf? tree) (weight-leaf tree) (cadddr tree))) (define (decode bits tree) (define (decode-1 bits current-branch) (if (null? bits) '() (let ((next-branch (choose-branch (car bits) current-branch))) (if (leaf? next-branch) (cons (symbol-leaf next-branch) (decode-1 (cdr bits) tree)) (decode-1 (cdr bits) next-branch))))) (decode-1 bits tree)) (define (choose-branch bit branch) (cond ((= bit 0) (left-branch branch)) ((= bit 1) (right-branch branch)) (else (error "bad bit -- CHOOSE-BRANCH" bit)))) (define (test s-exp) (display s-exp) (newline)) (define sample-tree (make-code-tree (make-leaf 'A 4) (make-code-tree (make-leaf 'B 2) (make-code-tree (make-leaf 'D 1) (make-leaf 'C 1))))) (define sample-message '(0 1 1 0 0 1 0 1 0 1 1 1 0)) (test (decode sample-message sample-tree))

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• Resizing image algorithm in python

  - by hippocampus

  So, I'm learning my self python by this tutorial and I'm stuck with exercise number 13 which says: Write a function to uniformly shrink or enlarge an image. Your function should take an image along with a scaling factor. To shrink the image the scale factor should be between 0 and 1 to enlarge the image the scaling factor should be greater than 1. This is not meant as a question about PIL, but to ask which algorithm to use so I can code it myself. I've found some similar questions like this, but I dunno how to translate this into python. Any help would be appreciated. I've come to this: import image win = image.ImageWin() img = image.Image("cy.png") factor = 2 W = img.getWidth() H = img.getHeight() newW = int(W*factor) newH = int(H*factor) newImage = image.EmptyImage(newW, newH) for col in range(newW): for row in range(newH): p = img.getPixel(col,row) newImage.setPixel(col*factor,row*factor,p) newImage.draw(win) win.exitonclick() I should do this in a function, but this doesn't matter right now. Arguments for function would be (image, factor). You can try it on OP tutorial in ActiveCode. It makes a stretched image with empty columns :.

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• should this database table be normalized?

  - by oo

  i have taken over a database that stores fitness information and we were having a debate about a certain table and whether it should stay as one table or get broken up into three tables. Today, there is one table called: workouts that has the following fields id, exercise_id, reps, weight, date, person_id So if i did 2 sets of 3 different exercises on one day, i would have 6 records in that table for that day. for example: id, exercise_id, reps, weight, date, person_id 1, 1, 10, 100, 1/1/2010, 10 2, 1, 10, 100, 1/1/2010, 10 3, 1, 10, 100, 1/1/2010, 10 4, 2, 10, 100, 1/1/2010, 10 5, 2, 10, 100, 1/1/2010, 10 6, 2, 10, 100, 1/1/2010, 10 So the question is, given that there is some redundant data (date, personid, exercise_id) in multiple records, should this be normalized to three tables WorkoutSummary: - id - date - person_id WorkoutExercise: - id - workout_id (foreign key into WorkoutSummary) - exercise_id WorkoutSets: - id - workout_exercise_id (foreign key into WorkoutExercise) - reps - weight I would guess the downside is that the queries would be slower after this refactoring as now we would need to join 3 tables to do the same query that had no joins before. The benefit of the refactoring allows up in the future to add new fields at the workout summary level or the exercise level with out adding in more duplication. any feedback on this debate?

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• populate UITableView from json

  - by mcgrailm

  Hello all working on my building my first iDevice app and I am trying to populate a UITableView with data from json result I can get it to load from plist array no propblem and I can even see my json the problem I'm having is that the UITableView never gets to see the json results please bare with me as this is first time with obj-c or anything like it in my .h file @interface TableViewViewController : UIViewController <UITableViewDataSource, UITableViewDelegate> { NSArray *exercises; NSMutableData *responseData; } in my .m file - (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section { return exercises.count; } - (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath { //create a cell UITableViewCell *cell = [[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:@"cell"]; // fill it with contnets cell.textLabel.text = [exercises objectAtIndex:indexPath.row]; // return it return cell; } // Implement viewDidLoad to do additional setup after loading the view, typically from a nib. - (void)viewDidLoad { responseData = [[NSMutableData data] retain]; NSURLRequest *request = [NSURLRequest requestWithURL:[NSURL URLWithString:@"http://url_to_json"]]; [[NSURLConnection alloc] initWithRequest:request delegate:self ]; // load from plist //NSString *myfile = [[NSBundle mainBundle] pathForResource:@"exercise" ofType:@"plist"]; //exercises = [[NSArray alloc] initWithContentsOfFile:myfile]; [super viewDidLoad]; } - (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response { [responseData setLength:0]; } - (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data { [responseData appendData:data]; } - (void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error { NSLog(@"Connection failed: %@", [error description]); } - (void)connectionDidFinishLoading:(NSURLConnection *)connection { [connection release]; NSString *responseString = [[NSString alloc] initWithData:responseData encoding:NSUTF8StringEncoding]; [responseData release]; NSDictionary *dictionary = [responseString JSONValue]; NSArray *response = [dictionary objectForKey:@"response"]; exercises = [[NSArray alloc] initWithArray:response]; }

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• What are the primitive Forth operators?

  - by Barry Brown

  I'm interested in implementing a Forth system, just so I can get some experience building a simple VM and runtime. When starting in Forth, one typically learns about the stack and its operators (DROP, DUP, SWAP, etc.) first, so it's natural to think of these as being among the primitive operators. But they're not. Each of them can be broken down into operators that directly manipulate memory and the stack pointers. Later one learns about store (!) and fetch (@) which can be used to implement DUP, SWAP, and so forth (ha!). So what are the primitive operators? Which ones must be implemented directly in the runtime environment from which all others can be built? I'm not interested in high-performance; I want something that I (and others) can learn from. Operator optimization can come later. (Yes, I'm aware that I can start with a Turing machine and go from there. That's a bit extreme.) Edit: What I'm aiming for is akin to bootstrapping an operating system or a new compiler. What do I need do implement, at minimum, so that I can construct the rest of the system out of those primitive building blocks? I won't implement this on bare hardware; as an educational exercise, I'd write my own minimal VM.

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• How to effectively use WorkbookBeforeClose event correctly?

  - by Ahmad

  On a daily basis, a person needs to check that specific workbooks have been correctly updated with Bloomberg and Reuters market data ie. all data has pulled through and that the 'numbers look correct'. In the past, people were not checking the 'numbers' which led to inaccurate uploads to other systems etc. The idea is that 'something' needs to be developed to prevent the use from closing/saving the workbook unless he/she has checked that the updates are correct/accurate. The numbers look correct action is purely an intuitive exercise, thus will not be coded in any way. The simple solution was to prompt users prior to closing the specific workbook to verify that the data has been checked. Using VSTO SE for Excel 2007, an Add-in was created which hooks into the WorkbookBeforeClose event which is initialised in the add-in ThisAddIn_Startup private void wb_BeforeClose(Xl.Workbook wb, ref bool cancel) { //.... snip ... if (list.Contains(wb.Name)) { DailogResult result = MessageBox.Show("some message", "sometitle", MessageBoxButtons.YesNo); if (result != DialogResult.Yes) { cancel = true; // i think this prevents the whole application from closing } } } I have found the following ThisApplication.WorkbookBeforeSave vs ThisWorkbook.Application.WorkbookBeforeSave which recommends that one should use the ThisApplication.WorkbookBeforeClose event which I think is what I am doing since will span all files opened. The issue I have with the approach is that assuming that I have several files open, some of which are in my list, the event prevents Excel from closing all files sequentially. It now requires each file to be closed individually. Am I using the event correctly and is this effective & efficient use of the event? Should I use the Application level event or document level event? Is there a way to prevent the above behaviour? Any other suggestions are welcomed VS 2005 with VSTO SE

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• Distutils - Where Am I going wrong?

  - by RJBrady

  I wanted to learn how to create python packages, so I visited http://docs.python.org/distutils/index.html. For this exercise I'm using Python 2.6.2 on Windows XP. I followed along with the simple example and created a small test project: person/ setup.py person/ __init__.py person.py My person.py file is simple: class Person(object): def __init__(self, name="", age=0): self.name = name self.age = age def sound_off(self): print "%s %d" % (self.name, self.age) And my setup.py file is: from distutils.core import setup setup(name='person', version='0.1', packages=['person'], ) I ran python setup.py sdist and it created MANIFEST, dist/ and build/. Next I ran python setup.py install and it installed it to my site packages directory. I run the python console and can import the person module, but I cannot import the Person class. >>>import person >>>from person import Person Traceback (most recent call last): File "<stdin>", line 1, in <module> ImportError: cannot import name Person I checked the files added to site-packages and checked the sys.path in the console, they seem ok. Why can't I import the Person class. Where did I go wrong?

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• How to disable Safari Reader in a web page

  - by michael

  I'm curious to know more about what triggers the Reader option in Safari and what does not. I wouldn't plan to implement anything that would disable it, but curious as a technical exercise. Here is what I've learned so far with some basic playing around: You need at least one H tag It does not go by character count alone but by the number of P tags and length Probably looks for sentence breaks '.' and other criteria Safari will provide the 'Reader' if, with a H tag, and the following: 1 P tag, 2417 chars 4 P tags, 1527 chars 5 P tags, 1150 chars 6 P tags, 862 chars If you subtract 1 character from any of the above, the 'Reader' option is not available. I should note that the character count of the H tag plays a part but sadly did not realize this when I determined the results above. Assume 20+ characters for H tag and fixed throughout the results above. Some other interesting things: Setting <p style="display:none;"> for P tags removes them from the count Setting display to none, and then showing them 230ms later with Javascript avoided the Reader option too I'd be interested if anyone can determine this in full.

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• Passing custom Python objects to nosetests

  - by Rob

  I am attempting to re-organize our test libraries for automation and nose seems really promising. My question is, what is the best strategy for passing Python objects into nose tests? Our tests are organized in a testlib with a bunch of modules that exercise different types of request operations. Something like this: testlib \-testmoda \-testmodb \-testmodc In some cases the test modules (i.e. testmoda) is nothing but test_something(), test_something2() functions while in some cases we have a TestModB class in testmob with the test_anotherthing1(), test_anotherthing2() functions. The cool thing is that nose easily finds both. Most of those test functions are request factory stuff that can easily share a single connection to our server farm. Thus we do a lot of test_something1(cnn), TestModB.test_anotherthing2(cnn), etc. Currently we don't use nose, instead we have a hodge-podge of homegrown driver scripts with hard-coded lists of tests to execute. Each of those driver scripts creates its own connection object. Maintaining those scripts and the connection minutia is painful. I'd like to take free advantage of nose's beautiful discovery functionality, passing in a connection object of my choosing. Thanks in advance! Rob P.S. The connection objects are not pickle-able. :(

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• Printing Arrays from Structs

  - by Carlll

  I've been stumped for a few hours on an exercise where I must use functions to build up an array inside a struct and print it. In my current program, it compiles but crashes upon running. #define LIM 10 typedef char letters[LIM]; typedef struct { int counter; letters words[LIM]; } foo; int main(int argc, char **argv){ foo apara; structtest(apara, LIM); print_struct(apara); } int structtest(foo *p, int limit){ p->counter = 0; int i =0; for(i; i< limit ;i++){ strcpy(p->words[p->counter], "x"); //only filling arrays with 'x' as an example p->counter ++; } return; I do believe it's due to my incorrect usage/combination of pointers. I've tried adjusting them, but either an 'incompatible types' error is produced, or the array is seemingly blank } void print_struct(foo p){ printf(p.words); } I haven't made it successfully up to the print_struct stage, but I'm unsure whether p.words is the correct item to be calling. In the output, I would expect the function to return an array of x's. I apologize in advance if I've made some sort of grievous "I should already know this" C mistake. Thanks for your help.

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• Why This Maintainability Index Increase?

  - by Timothy

  I would be appreciative if someone could explain to me the difference between the following two pieces of code in terms of Visual Studio's Code Metrics rules. Why does the Maintainability Index increase slightly if I don't encapsulate everything within using ( )? Sample 1 (MI score of 71) public static String Sha1(String plainText) { using (SHA1Managed sha1 = new SHA1Managed()) { Byte[] text = Encoding.Unicode.GetBytes(plainText); Byte[] hashBytes = sha1.ComputeHash(text); return Convert.ToBase64String(hashBytes); } } Sample 2 (MI score of 73) public static String Sha1(String plainText) { Byte[] text, hashBytes; using (SHA1Managed sha1 = new SHA1Managed()) { text = Encoding.Unicode.GetBytes(plainText); hashBytes = sha1.ComputeHash(text); } return Convert.ToBase64String(hashBytes); } I understand metrics are meaningless outside of a broader context and understanding, and programmers should exercise discretion. While I could boost the score up to 76 with return Convert.ToBase64String(sha1.ComputeHash(Encoding.Unicode.GetBytes(plainText))), I shouldn't. I would clearly be just playing with numbers and it isn't truly any more readable or maintainable at that point. I am curious though as to what the logic might be behind the increase in this case. It's obviously not line-count.

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• Using MD5 to generate an encryption key from password?

  - by Charles

  I'm writing a simple program for file encryption. Mostly as an academic exercise but possibly for future serious use. All of the heavy lifting is done with third-party libraries, but putting the pieces together in a secure manner is still quite a challenge for the non-cryptographer. Basically, I've got just about everything working the way I think it should. I'm using 128-bit AES for the encryption with a 128-bit key length. I want users to be able to enter in variable-length passwords, so I decided to hash the password with MD5 and then use the hash as the key. I figured this was acceptable--the key is always supposed to be a secret, so there's no reason to worry about collision attacks. Now that I've implemented this, I ran across a couple articles indicating that this is a bad idea. My question is: why? If a good password is chosen, the cipher is supposed to be strong enough on its own to never reveal the key except via an extraordinary (read: currently infeasible) brute-force effort, right? Should I be using something like PBKDF2 to generate the key or is that just overkill for all but the most extreme cryptographic applications?

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