subclass

I was surprised to to learn that a class variable of a subclass can't access a class variable of the parent without specifically indicating the class name of the parent: >>> class A(object): ... x = 0 ... >>> class B(A): ... y = x+1 ... Traceback (most recent call last): File "<stdin>", line 1, in <module> File "<stdin>", line 2, in B NameError: name 'x' is not defined >>> class B(A): ... y = A.x + 1 ... >>> B.x 0 >>> B.y 1 Why is it that in defining B.y I have to refer to A.x and not just x? This is counter to my intuition from instance variables, and since I can refer to B.x after B is

Let's say that I have a class Suit and four subclasses of suit: Heart, Spade, Diamond, Club. class Suit: ... class Heart(Suit): ... class Spade(Suit): ... class Diamond(Suit): ... class Club(Suit): ... I have a method which receives a suit as a parameter, which is a class object, not an instance. More precisely, it may receive only one of the four values: Heart, Spade, Diamond, Club. How can I make an assertion which ensures such a thing? Something like: def my_method(suit): assert(suit subclass of Suit) ... I'm using Python 3. You can use issubclass() like this assert issubclass(suit, Suit) .

Is there a way to make the background of a UIView a gradient without subclassing it? I'd rather not use an image file to accomplish this either. It just seems obtuse to have to subclass UIView just to draw a gradient for the background. rpetrich You can use +[UIColor colorWithPatternImage:] to produce a patterned background. Example (bring your own CGGradient): // Allocate color space CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB(); // Allocate bitmap context CGContextRef bitmapContext = CGBitmapContextCreate(NULL, 320, 480, 8, 4 * 320, colorSpace, kCGImageAlphaNoneSkipFirst); /

Background and goal Goal: I want to rotate and flip a UITextView . ( Why: see my previous question ) Problem: If I do the transform directly on the UITextView , the text layout gets messed up for some unknown reason. Solution: Put the UITextView in a UIView container, and then do the transform on the container. New problem: Auto Layout (or any sort of layout) on the rotated view becomes a major headache . Proposed solution: Make a subclass of UIView that acts as an additional container for the rotated and flipped UIView . Auto Layout should then work on this custom view. Current Problem It

Does calling [super init] do the same thing in a category as a subclass? If not, what's the difference? In order to understand this, it's probably important to understand the way an object is stored during runtime. There is a class object 1 , which holds all the method implementations, and separately, there is a structure with the storage for the instance's variables. All instances of a class share the one class object. When you call a method on an instance, the compiler turns that into a call to objc_msgSend ; the method implementation is looked up in the class object, and then run with the