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• Can a binary tree or tree be always represented in a Database table as 1 table and self-referencing?

  - by Jian Lin

  I didn't feel this rule before, but it seems that a binary tree or any tree (each node can have many children but children cannot point back to any parent), then this data structure can be represented as 1 table in a database, with each row having an ID for itself and a parentID that points back to the parent node. That is in fact the classical Employee - Manager diagram: one boss can have many people under him... and each person under him can have n people under him, etc. This is a tree structure and is represented in database books as a common example as a single table Employee.

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• Load external swf from a button in external swf and unload self?

  - by ChristinaR

  Hello, I am an uber n00b to flash AS3. And it is not my intention to sound like a complete moron, but honestly, I have had a hard enough time figuring out just how to load an external .swf into my main file! And now my friend is asking me if I could please add a button within the external .swf which will unload itself and load a new on in its place... I have looked around in the forums for an answer for a while now and I believe it is time for me to break down, admit defeat, and ask for help. Can someone please tell me it's not that difficult..? Surely it is possible... Thank you in advance for any advice at all! I am looking forward to the time when I can post a response here!

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• How to (legitimately) access files after putting self into chrooted sandbox?

  - by unknown google user

  Changing a Linux C++ program which gives the user limited file access. Thus the program chroots itself to a sandbox with the files the user can get at. All worked well. Now, however, the program needs to access some files for its own needs (not the user's) but they are outside the sandbox. I know chroot allows access to files opened before the chroot but in this case the needed files could a few among many hundreds so it is obviously impractical to open them all just for the couple that might be required. Is there any way to get at the files?

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• Trouble using South with Django and Heroku

  - by Dan

  I had an existing Django project that I've just added South to. I ran syncdb locally. I ran manage.py schemamigration app_name locally I ran manage.py migrate app_name --fake locally I commit and pushed to heroku master I ran syncdb on heroku I ran manage.py schemamigration app_name on heroku I ran manage.py migrate app_name on heroku I then receive this: $ heroku run python notecard/manage.py migrate notecards Running python notecard/manage.py migrate notecards attached to terminal... up, run.1 Running migrations for notecards: - Migrating forwards to 0005_initial. > notecards:0003_initial Traceback (most recent call last): File "notecard/manage.py", line 14, in <module> execute_manager(settings) File "/app/lib/python2.7/site-packages/django/core/management/__init__.py", line 438, in execute_manager utility.execute() File "/app/lib/python2.7/site-packages/django/core/management/__init__.py", line 379, in execute self.fetch_command(subcommand).run_from_argv(self.argv) File "/app/lib/python2.7/site-packages/django/core/management/base.py", line 191, in run_from_argv self.execute(*args, **options.__dict__) File "/app/lib/python2.7/site-packages/django/core/management/base.py", line 220, in execute output = self.handle(*args, **options) File "/app/lib/python2.7/site-packages/south/management/commands/migrate.py", line 105, in handle ignore_ghosts = ignore_ghosts, File "/app/lib/python2.7/site-packages/south/migration/__init__.py", line 191, in migrate_app success = migrator.migrate_many(target, workplan, database) File "/app/lib/python2.7/site-packages/south/migration/migrators.py", line 221, in migrate_many result = migrator.__class__.migrate_many(migrator, target, migrations, database) File "/app/lib/python2.7/site-packages/south/migration/migrators.py", line 292, in migrate_many result = self.migrate(migration, database) File "/app/lib/python2.7/site-packages/south/migration/migrators.py", line 125, in migrate result = self.run(migration) File "/app/lib/python2.7/site-packages/south/migration/migrators.py", line 99, in run return self.run_migration(migration) File "/app/lib/python2.7/site-packages/south/migration/migrators.py", line 81, in run_migration migration_function() File "/app/lib/python2.7/site-packages/south/migration/migrators.py", line 57, in <lambda> return (lambda: direction(orm)) File "/app/notecard/notecards/migrations/0003_initial.py", line 15, in forwards ('user', self.gf('django.db.models.fields.related.ForeignKey')(to=orm['auth.User'])), File "/app/lib/python2.7/site-packages/south/db/generic.py", line 226, in create_table ', '.join([col for col in columns if col]), File "/app/lib/python2.7/site-packages/south/db/generic.py", line 150, in execute cursor.execute(sql, params) File "/app/lib/python2.7/site-packages/django/db/backends/util.py", line 34, in execute return self.cursor.execute(sql, params) File "/app/lib/python2.7/site-packages/django/db/backends/postgresql_psycopg2/base.py", line 44, in execute return self.cursor.execute(query, args) django.db.utils.DatabaseError: relation "notecards_semester" already exists I have 3 models. Section, Semester, and Notecards. I've added one field to the Notecards model and I cannot get it added on Heroku. Thank you.

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• Basic drawing with Quartz 2D on iPhone

  - by wwrob

  My goal is to make a program that will draw points whenever the screen is touched. This is what I have so far: The header file: #import <UIKit/UIKit.h> @interface ElSimView : UIView { CGPoint firstTouch; CGPoint lastTouch; UIColor *pointColor; CGRect *points; int npoints; } @property CGPoint firstTouch; @property CGPoint lastTouch; @property (nonatomic, retain) UIColor *pointColor; @property CGRect *points; @property int npoints; @end The implementation file: //@synths etc. - (id)initWithFrame:(CGRect)frame { return self; } - (id)initWithCoder:(NSCoder *)coder { if(self = [super initWithCoder:coder]) { self.npoints = 0; } return self; } - (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event { UITouch *touch = [touches anyObject]; firstTouch = [touch locationInView:self]; lastTouch = [touch locationInView:self]; } - (void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event { UITouch *touch = [touches anyObject]; lastTouch = [touch locationInView:self]; points = (CGRect *)malloc(sizeof(CGRect) * ++npoints); points[npoints-1] = CGRectMake(lastTouch.x-15, lastTouch.y-15,30,30); [self setNeedsDisplay]; } - (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event { UITouch *touch = [touches anyObject]; lastTouch = [touch locationInView:self]; [self setNeedsDisplay]; } - (void)drawRect:(CGRect)rect { CGContextRef context = UIGraphicsGetCurrentContext(); CGContextSetLineWidth(context, 2.0); CGContextSetStrokeColorWithColor(context, [UIColor blackColor].CGColor); CGContextSetFillColorWithColor(context, pointColor.CGColor); for(int i=0; i<npoints; i++) CGContextAddEllipseInRect(context, points[i]); CGContextDrawPath(context, kCGPathFillStroke); } - (void)dealloc { free(points); [super dealloc]; } @end When I load this and click some points, it draws the first points normally, then then next points are drawn along with random ellipses (not even circles). Also I have another question: When is exactly drawRect executed?

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• How to break the following line of python

  - by FrederikNS

  Hello Stack Overflow, I have come upon a couple of lines of code similar to this one, but I'm unsure how I should break it: blueprint = Blueprint(self.blueprint_map[str(self.ui.blueprint_combo.currentText())], runs=self.ui.runs_spin.text(), me=self.ui.me_spin.text(), pe=self.ui.pe_skill_combo.currentIndex()) Thanks in advance

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• How to make a self contained jQuery plugin that finds the tallest image height?

  - by Jannis

  I have been trying to make this to be a little jQuery plugin that I can reuse in the future without having to write the following into my actions.js file in full. This works when loaded in the same file where I set the height using my variable tallest. var tallest = null; $('.slideshow img').each(function(index) { if ($(this).height() >= tallest ) { tallest = $(this).height(); } }); $('.slideshow').height(tallest); This works and will cycle through all the items, then set the value of tallest to the greatest height found. The following however does not work: This would be the plugin, loaded from its own file (before the actions.js file that contains the parts using this): (function($){ $.fn.extend({ tallest: function() { var tallest = null; return this.each(function() { if ($(this).height() >= tallest ) { tallest = $(this).height(); } }); } }); })(jQuery); Once loaded I am trying to use it as follows: $('.slideshow img').tallest(); $('.slideshow').height(tallest); However the above two lines return an error of 'tallest is undefined'. How can I make this work? Any ideas would be appreciated. Thinking about this even more the perfect usage of this would be as follows: $('.container').height(tallest('.container item')); But I wouldn't even know where to begin to get this to work in the manner that you pass the object to be measured into the function by adding it into the brackets of the function name. Thanks for reading, Jannis

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• Pass information to php file from javascript while restricting user from doing it their self?

  - by Sean Madigan

  I am making a game where the battle system uses javascript to battle. At the end of the battle you either win or lose. If the user wins, I need to update the mysql database with the XP they earned. The best way I can think of doing this is to have the javascript run an ajax function when the user wins that POSTs something like addxp.php?amount=235, but if I do that then the user can easilly look at the source and see that they can just enter in that page themself to update their xp without battling. But this is the only way I know how to do it? Help please :-/

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• Django save_m2m() and excluded field

  - by jul

  hi, in a ModelForm I replaced a field by excluding it and adding a new one with the same name, as shown below in AddRestaurantForm. When saving the form with the code shown below, I get an error in form.save_m2m() ("Truncated incorrect DOUBLE value"), which seems to be due to the function to attempt to save the tag field, while it is excluded. Is the save_m2m() function supposed to save excluded fields? Is there anything wrong in my code? Thanks Jul (...) new_restaurant = form.save(commit=False) new_restaurant.city = city new_restaurant.save() tags = form.cleaned_data['tag'] if(tags!=''): tags=tags.split(',') for t in tags: tag, created = Tag.objects.get_or_create(name = t.strip()) tag.save() new_restaurant.tag.add(tag) new_restaurant.save() form.save_m2m() models.py class Tag(models.Model): name = models.CharField(max_length=100, unique=True) class Restaurant(models.Model): name = models.CharField(max_length=50) city=models.ForeignKey(City) category=models.ManyToManyField(Category) tag=models.ManyToManyField(Tag, blank=True, null=True) forms.py class AddRestaurantForm(ModelForm): name = forms.CharField(widget=forms.TextInput(attrs=classtext)) city = forms.CharField(widget=forms.TextInput(attrs=classtext), max_length=100) tag = forms.CharField(widget=forms.TextInput(attrs=classtext), required=False) class Meta: model = Restaurant exclude = ('city','tag') Traceback: File "/var/lib/python-support/python2.5/django/core/handlers/base.py" in get_response 92. response = callback(request, *callback_args, **callback_kwargs) File "/home/jul/atable/../atable/resto/views.py" in addRestaurant 498. form.save_m2m() File "/var/lib/python-support/python2.5/django/forms/models.py" in save_m2m 75. f.save_form_data(instance, cleaned_data[f.name]) File "/var/lib/python-support/python2.5/django/db/models/fields/ related.py" in save_form_data 967. setattr(instance, self.attname, data) File "/var/lib/python-support/python2.5/django/db/models/fields/ related.py" in set 627. manager.add(*value) File "/var/lib/python-support/python2.5/django/db/models/fields/ related.py" in add 430. self._add_items(self.source_col_name, self.target_col_name, *objs) File "/var/lib/python-support/python2.5/django/db/models/fields/ related.py" in _add_items 497. [self._pk_val] + list(new_ids)) File "/var/lib/python-support/python2.5/django/db/backends/util.py" in execute 19. return self.cursor.execute(sql, params) File "/var/lib/python-support/python2.5/django/db/backends/mysql/ base.py" in execute 84. return self.cursor.execute(query, args) File "/var/lib/python-support/python2.5/MySQLdb/cursors.py" in execute 168. if not self._defer_warnings: self._warning_check() File "/var/lib/python-support/python2.5/MySQLdb/cursors.py" in _warning_check 82. warn(w[-1], self.Warning, 3) File "/usr/lib/python2.5/warnings.py" in warn 62. globals) File "/usr/lib/python2.5/warnings.py" in warn_explicit 102. raise message Exception Type: Warning at /restaurant/add/ Exception Value: Truncated incorrect DOUBLE value: 'a'

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• t-sql - find differences for pk's in a single table (Self join?)

  - by Pace

  Hi Experts, My situation is this. I have a table of products with a pk "Parent" which has "Components" The data looks something like this Parent(PK) Component Car1 Wheel Car1 Tyre Car1 Roof Car2 Alloy Car2 Tyre Car2 Roof Car3 Alloy Car3 Tyre Car3 Roof Car3 Leather Seats Now what I want to do is some query that I can feed two codes in and see the differences... IE If I feed in "Car1", "Car2" it would return something like; Parent Component Car1 Wheel Car2 Alloy As this is the difference between the two. If I said "Car1", "Car3" I would expect; Parent Component Car1 Wheel Car3 Alloy Car3 Leather Seats Your help with this matter would be greatly appreciated.

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• Passing parameter to base class constructor or using instance variable?

  - by deamon

  All classes derived from a certain base class have to define an attribute called "path". In the sense of duck typing I could rely upon definition in the subclasses: class Base: pass # no "path" variable here def Sub(Base): def __init__(self): self.path = "something/" Another possiblity would be to use the base class constructor: class Base: def __init__(self, path): self.path = path def Sub(Base): def __init__(self): super().__init__("something/") What would you prefer and why? Is there a better way?

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• How can I create a self-consistent .jar file with Eclipse?

  - by Roman

  I wrote my Java application in Eclipse. Now I would like to generate a .jar file which can be run on other systems from the command line. Is there a easy way to do it in Eclipse? In particular I am wondering what should I do with the jar files of external library that I use (should it be included into my .jar file?). Moreover, should I generate some manifest files?

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• Error with python decorator

  - by Timmy

  I get this error object has no attribute 'im_func' with this class Test(object): def __init__(self, f): self.func = f def __call__( self, *args ): return self.func(*args) pylons code: class TestController(BaseController): @Test def index(self): return 'hello world'

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• Does my function right on python?

  - by Ali Ismayilov

  Write a function which takes a string argument, and creates and returns an Employee object containing details of the employee specified by the string. The string should be assumed to have the format 12345 25000 Consultant Bart Simpson The first three items in the line will be the payroll number, salary and job title and the rest of the line will be the name. There will be no spaces in the job title but there may be one or more spaces in the name. My function: def __str__(self): return format(self.payroll, "d") + format(self.salary, "d") + ' ' \ + self.jobtitle + self.name

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• Is there any issues with always self closing empty tags in html?

  - by Simon

  Are there any browser issues with always collapsing empty tags in html. So for example and empty head can be written like this <head></head> but is can also be written like this <head/> Will the second case cause issues in any scenerio? Thanks

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• [Errno 10061] No connection could be made because the target machine actively refused it

  - by user551717

  I've tried to connect to my local machine every time I try and run my program. I am a nub, so it's probably a simple mistake somewhere. def connect(self): self.conn = socket.socket(socket.AF_INET, socket.SOCK_STREAM) self.conn.connect((self.host,self.port)) That is the code causing the error. The host and port are defined. Why is it giving me this error report? [Errno 10061] No connection could be made because the target machine actively refused it

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• How to add a constructor to a subclassed numeric type?

  - by abbot

  I want to subclass a numeric type (say, int) in python and give it a shiny complex constructor. Something like this: class NamedInteger(int): def __init__(self, value): super(NamedInteger, self).__init__(value) self.name = 'pony' def __str__(self): return self.name x = NamedInteger(5) print x + 3 print str(x) This works fine under Python 2.4, but Python 2.6 gives a deprecation warning. What is the best way to subclass a numeric type and to redefine constructors for builtin types in newer Python versions?

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• Python unittest: Generate multiple tests programmatically?

  - by Rosarch

  I have a function to test, under_test, and a set of expected input/output pairs: [ (2, 332), (234, 99213), (9, 3), # ... ] I would like each one of these input/output pairs to be tested in its own test_* method. Is that possible? This is sort of what I want, but forcing every single input/output pair into a single test: class TestPreReqs(unittest.TestCase): def setUp(self): self.expected_pairs = [(23, 55), (4, 32)] def test_expected(self): for exp in self.expected_pairs: self.assertEqual(under_test(exp[0]), exp[1]) if __name__ == '__main__': unittest.main()

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• How to make an custom button with an self-stretching image?

  - by mystify

  I slightly remember that there is an class which is capable of stretching an image in such a way, that the first x pixels and the last y pixels won't get stretched. For example if you have an button image with round corners, you would want those round corners to stay intact while the middle part of that image gets stretched.

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• Cocos2d score resetting is messing up (long post warning)

  - by Jhon Doe

  The score is not resetting right at all,I am trying to make a high score counter where every time you passed previous high score it will update.However, right now it is resetting during the game. For example if I had high score of 2 during the game it will take 3 points just to put it up to 3 as high score instead of keep going up until it is game over. I have came to the conclusion that I need to reset it in gameoverlayer so it won't reset during game. I have been trying to to do this but no luck. hello world ./h #import "cocos2d.h" // HelloWorldLayer @interface HelloWorldLayer : CCLayer { int _score; int _oldScore; CCLabelTTF *_scoreLabel; } @property (nonatomic, assign) CCLabelTTF *scoreLabel; hello world init ./m _score = [[NSUserDefaults standardUserDefaults] integerForKey:@"score"]; _oldScore = -1; self.scoreLabel = [CCLabelTTF labelWithString:@"" dimensions:CGSizeMake(100, 50) alignment:UITextAlignmentRight fontName:@"Marker Felt" fontSize:32]; _scoreLabel.position = ccp(winSize.width - _scoreLabel.contentSize.width, _scoreLabel.contentSize.height); _scoreLabel.color = ccc3(255,0,0); [self addChild:_scoreLabel z:1]; hello world implement ./m - (void)update:(ccTime)dt { NSMutableArray *projectilesToDelete = [[NSMutableArray alloc] init]; CGRect projectileRect = CGRectMake( projectile.position.x - (projectile.contentSize.width/2), projectile.position.y - (projectile.contentSize.height/2), projectile.contentSize.width, projectile.contentSize.height); BOOL monsterHit = FALSE; NSMutableArray *targetsToDelete = [[NSMutableArray alloc] init]; for (CCSprite *target in _targets) { CGRect targetRect = CGRectMake( target.position.x - (target.contentSize.width/2), target.position.y - (target.contentSize.height/2), target.contentSize.width, target.contentSize.height); if (CGRectIntersectsRect(projectileRect, targetRect)) { CCParticleFire* explosion = [[CCParticleFire alloc] initWithTotalParticles:200]; explosion.texture =[[CCTextureCache sharedTextureCache] addImage:@"sun.png"]; explosion.autoRemoveOnFinish = YES; explosion.startSize = 20.0f; explosion.speed = 70.0f; explosion.anchorPoint = ccp(0.5f,0.5f); explosion.position = target.position; explosion.duration = 1.0f; [self addChild:explosion z:11]; [explosion release]; monsterHit = TRUE; Monster *monster = (Monster *)target; monster.hp--; if (monster.hp <= 0) { [targetsToDelete addObject:target]; [[SimpleAudioEngine sharedEngine] playEffect:@"splash.wav"]; _score ++; } break; } } for (CCSprite *target in targetsToDelete) { [_targets removeObject:target]; [self removeChild:target cleanup:YES]; } if (targetsToDelete.count > 0) { [ projectilesToDelete addObject:projectile]; } [targetsToDelete release]; if (_score > _oldScore) { _oldScore = _score; [_scoreLabel setString:[NSString stringWithFormat:@"score%d", _score]]; [[NSUserDefaults standardUserDefaults] setInteger:_oldScore forKey:@"score"]; _score = 0; } } - (void)update:(ccTime)dt { NSMutableArray *projectilesToDelete = [[NSMutableArray alloc] init]; CGRect projectileRect = CGRectMake( projectile.position.x - (projectile.contentSize.width/2), projectile.position.y - (projectile.contentSize.height/2), projectile.contentSize.width, projectile.contentSize.height); BOOL monsterHit = FALSE; NSMutableArray *targetsToDelete = [[NSMutableArray alloc] init]; for (CCSprite *target in _targets) { CGRect targetRect = CGRectMake( target.position.x - (target.contentSize.width/2), target.position.y - (target.contentSize.height/2), target.contentSize.width, target.contentSize.height); if (CGRectIntersectsRect(projectileRect, targetRect)) { CCParticleFire* explosion = [[CCParticleFire alloc] initWithTotalParticles:200]; explosion.texture =[[CCTextureCache sharedTextureCache] addImage:@"sun.png"]; explosion.autoRemoveOnFinish = YES; explosion.startSize = 20.0f; explosion.speed = 70.0f; explosion.anchorPoint = ccp(0.5f,0.5f); explosion.position = target.position; explosion.duration = 1.0f; [self addChild:explosion z:11]; [explosion release]; monsterHit = TRUE; Monster *monster = (Monster *)target; monster.hp--; if (monster.hp <= 0) { [targetsToDelete addObject:target]; [[SimpleAudioEngine sharedEngine] playEffect:@"splash.wav"]; _score ++; } break; } } for (CCSprite *target in targetsToDelete) { [_targets removeObject:target]; [self removeChild:target cleanup:YES]; } if (targetsToDelete.count > 0) { [projectilesToDelete addObject:projectile]; } [targetsToDelete release]; if (_score > _oldScore) { _oldScore = _score; [_scoreLabel setString:[NSString stringWithFormat:@"score%d", _score]]; [[NSUserDefaults standardUserDefaults] setInteger:_oldScore forKey:@"score"]; _score = 0; } The game overlayer .h file game over @interface GameOverLayer : CCLayerColor { CCLabelTTF *_label; CCSprite * background; int _score; int _oldScore; } @property (nonatomic, retain) CCLabelTTF *label; @end @interface GameOverScene : CCScene { GameOverLayer *_layer; } @property (nonatomic, retain) GameOverLayer *layer; @end .m file gameover #import "GameOverLayer.h" #import "HelloWorldLayer.h" #import "MainMenuScene.h" @implementation GameOverScene @synthesize layer = _layer; - (id)init { if ((self = [super init])) { self.layer = [GameOverLayer node]; [self addChild:_layer]; } return self; } - (void)dealloc { [_layer release]; _layer = nil; [super dealloc]; } @end @implementation GameOverLayer @synthesize label = _label; -(id) init { if( (self=[super initWithColor:ccc4(0,0,0,0)] )) { CGSize winSize = [[CCDirector sharedDirector] winSize]; self.label = [CCLabelTTF labelWithString:@"" fontName:@"Arial" fontSize:32]; _label.color = ccc3(225,0,0); _label.position = ccp(winSize.width/2, winSize.height/2); [self addChild:_label]; [self runAction:[CCSequence actions: [CCDelayTime actionWithDuration:3], [CCCallFunc actionWithTarget:self selector:@selector(gameOverDone)], nil]]; _score=0; }

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• programming in lua, objects

  - by anon

  Sample code: function Account:new (o) o = o or {} -- create object if user does not provide one setmetatable(o, self) self.__index = self return o end taken from: http://www.lua.org/pil/16.1.html What is the purpose of the: self.__index = self line? And why is it executed every time an object is created?

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• URL redirection if wrong url

  - by xRobot

  I have this method in my book model: def get_absolute_url(self): return "/book/%s/%s/%i/%i/" % ( self.book_title, self.book_editor, self.book_pages, self.id) So the urls of each book are like this: example.com/book/the-bible/gesu-crist/938/12/ I want that if there is an error in the url, then I get redirected to the real url by using book.id in the end of the url. For example if I go to: example.com/book/A-bible/gesu-crist/938/12/ the I will get redirected to: example.com/book/the-bible/gesu-crist/938/12/ How can I do that ?

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• How to make every Class Method call a specified method before execution?

  - by norm

  I want to make my Python Class behave in such a way that when any Class method is called a default method is executed first without explicitly specifying this in the called Class. An example may help :) Class animals: def _internalMethod(): self.respires = True def cat(): self._internalMethod() self.name = 'cat' def dog(): self._internalMethod() self.name = 'dog' I want _internalMethod() to be called automatically when any method is called from an instance of animals, rather than stating it explicitly in the def of each method. Is there an elegant way to do this? Cheers,

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• unrecognized selector sent to instance while trying to add an object to a mutable array

  - by madpoet

  I'm following the "Your Second iOS App" and I decided to play with the code to understand Objective C well... What I'm trying to do is simply adding an object to a mutable array in a class. Here are the classes: BirdSighting.h #import <Foundation/Foundation.h> @interface BirdSighting : NSObject @property (nonatomic, copy) NSString *name; @property (nonatomic, copy) NSString *location; @property (nonatomic, copy) NSDate *date; -(id) initWithName: (NSString *) name location:(NSString *) location date:(NSDate *) date; @end BirdSighting.m #import "BirdSighting.h" @implementation BirdSighting -(id) initWithName:(NSString *)name location:(NSString *)location date:(NSDate *)date { self = [super init]; if(self) { _name = name; _location = location; _date = date; return self; } return nil; } @end BirdSightingDataController.h #import <Foundation/Foundation.h> @class BirdSighting; @interface BirdSightingDataController : NSObject @property (nonatomic, copy) NSMutableArray *masterBirdSightingList; - (NSUInteger) countOfList; - (BirdSighting *) objectInListAtIndex: (NSUInteger) theIndex; - (void) addBirdSightingWithSighting: (BirdSighting *) sighting; @end BirdSightingDataController.m #import "BirdSightingDataController.h" @implementation BirdSightingDataController - (id) init { if(self = [super init]) { NSMutableArray *sightingList = [[NSMutableArray alloc] init]; self.masterBirdSightingList = sightingList; return self; } return nil; } -(NSUInteger) countOfList { return [self.masterBirdSightingList count]; } - (BirdSighting *) objectInListAtIndex: (NSUInteger) theIndex { return [self.masterBirdSightingList objectAtIndex:theIndex]; } - (void) addBirdSightingWithSighting: (BirdSighting *) sighting { [self.masterBirdSightingList addObject:sighting]; } @end And this is where I'm trying to add a BirdSighting instance to the mutable array: #import "BirdsMasterViewController.h" #import "BirdsDetailViewController.h" #import "BirdSightingDataController.h" #import "BirdSighting.h" @implementation BirdsMasterViewController - (void)awakeFromNib { [super awakeFromNib]; BirdSightingDataController *dataController = [[BirdSightingDataController alloc] init]; NSDate *date = [NSDate date]; BirdSighting *sighting = [[[BirdSighting alloc] init] initWithName:@"Ebabil" location:@"Ankara" date: date]; [dataController addBirdSightingWithSighting: sighting]; NSLog(@"dataController: %@", dataController.masterBirdSightingList); self.dataController = dataController; } .......... @end It throws NSInvalidArgumentException in BirdSightingDataController addBirdSightingWithSighting method... What am I doing wrong?

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• factory class, wrong number of arguments being passed to subclass constructor

  - by Hugh Bothwell

  I was looking at Python: Exception in the separated module works wrong which uses a multi-purpose GnuLibError class to 'stand in' for a variety of different errors. Each sub-error has its own ID number and error format string. I figured it would be better written as a hierarchy of Exception classes, and set out to do so: class GNULibError(Exception): sub_exceptions = 0 # patched with dict of subclasses once subclasses are created err_num = 0 err_format = None def __new__(cls, *args): print("new {}".format(cls)) # DEBUG if len(args) and args[0] in GNULibError.sub_exceptions: print(" factory -> {} {}".format(GNULibError.sub_exceptions[args[0]], args[1:])) # DEBUG return super(GNULibError, cls).__new__(GNULibError.sub_exceptions[args[0]], *(args[1:])) else: print(" plain {} {}".format(cls, args)) # DEBUG return super(GNULibError, cls).__new__(cls, *args) def __init__(self, *args): cls = type(self) print("init {} {}".format(cls, args)) # DEBUG self.args = args if cls.err_format is None: self.message = str(args) else: self.message = "[GNU Error {}] ".format(cls.err_num) + cls.err_format.format(*args) def __str__(self): return self.message def __repr__(self): return '{}{}'.format(type(self).__name__, self.args) class GNULibError_Directory(GNULibError): err_num = 1 err_format = "destination directory does not exist: {}" class GNULibError_Config(GNULibError): err_num = 2 err_format = "configure file does not exist: {}" class GNULibError_Module(GNULibError): err_num = 3 err_format = "selected module does not exist: {}" class GNULibError_Cache(GNULibError): err_num = 4 err_format = "{} is expected to contain gl_M4_BASE({})" class GNULibError_Sourcebase(GNULibError): err_num = 5 err_format = "missing sourcebase argument: {}" class GNULibError_Docbase(GNULibError): err_num = 6 err_format = "missing docbase argument: {}" class GNULibError_Testbase(GNULibError): err_num = 7 err_format = "missing testsbase argument: {}" class GNULibError_Libname(GNULibError): err_num = 8 err_format = "missing libname argument: {}" # patch master class with subclass reference # (TO DO: auto-detect all available subclasses instead of hardcoding them) GNULibError.sub_exceptions = { 1: GNULibError_Directory, 2: GNULibError_Config, 3: GNULibError_Module, 4: GNULibError_Cache, 5: GNULibError_Sourcebase, 6: GNULibError_Docbase, 7: GNULibError_Testbase, 8: GNULibError_Libname } This starts out with GNULibError as a factory class - if you call it with an error number belonging to a recognized subclass, it returns an object belonging to that subclass, otherwise it returns itself as a default error type. Based on this code, the following should be exactly equivalent (but aren't): e = GNULibError(3, 'missing.lib') f = GNULibError_Module('missing.lib') print e # -> '[GNU Error 3] selected module does not exist: 3' print f # -> '[GNU Error 3] selected module does not exist: missing.lib' I added some strategic print statements, and the error seems to be in GNULibError.__new__: >>> e = GNULibError(3, 'missing.lib') new <class '__main__.GNULibError'> factory -> <class '__main__.GNULibError_Module'> ('missing.lib',) # good... init <class '__main__.GNULibError_Module'> (3, 'missing.lib') # NO! ^ why? I call the subclass constructor as subclass.__new__(*args[1:]) - this should drop the 3, the subclass type ID - and yet its __init__ is still getting the 3 anyway! How can I trim the argument list that gets passed to subclass.__init__?

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