subclass

How does python prevent a class from being subclassed? [duplicate]

由 时光总嘲笑我的痴心妄想 提交于 2019-11-29 18:00:20
问题 This question already has an answer here: Final classes in Python 3.x- something Guido isn't telling me? 4 answers I came across the following in the python docs: bool([x]) Convert a value to a Boolean, using the standard truth testing procedure. If x is false or omitted, this returns False; otherwise it returns True. bool is also a class, which is a subclass of int. Class bool cannot be subclassed further. Its only instances are False and True. I've never in my life wanted to subclass bool ,

What is the correct (or best) way to subclass the Python set class, adding a new instance variable?

由 大城市里の小女人 提交于 2019-11-29 17:29:17
问题 I'm implementing an object that is almost identical to a set, but requires an extra instance variable, so I am subclassing the built-in set object. What is the best way to make sure that the value of this variable is copied when one of my objects is copied? Using the old sets module, the following code worked perfectly: import sets class Fooset(sets.Set): def __init__(self, s = []): sets.Set.__init__(self, s) if isinstance(s, Fooset): self.foo = s.foo else: self.foo = 'default' f = Fooset([1

How to add constraints on inherited properties in a grails domain sub-class

由 半城伤御伤魂 提交于 2019-11-29 16:21:45
问题 Here's what I'd like to do: class A { String string static constraints = { string(maxSize:100) } } class B extends A { static constraints = { string(url:true) } } So class A should have some constraints and B should have the same plus additional constraints on the same property. I couldn't get that to work though and I can imagine that it would clash with the Table-per-Hierarchy concept. So I tried to work around that problem by introducing a Command object with class B's constraints which

Java: returning subclass in superclass method signature

由 纵然是瞬间 提交于 2019-11-29 16:12:35
问题 I'm working on a problem where there are several implementations of Foo , accompanied by several FooBuilder 's. While Foo 's share several common variables that need to be set, they also have distinct variables that require their respective FooBuilder to implement some specific functionality. For succinctness, I'd like to have the FooBuilder 's setters to use method chaining, like: public abstract class FooBuilder { ... public FooBuilder setA(int A) { this.A = A; return this; } ... } and

python subclasses

由 大城市里の小女人 提交于 2019-11-29 14:38:06
问题 I currently have a class called Polynomial, The initialization looks like this: def __init__(self, *termpairs): self.termdict = dict(termpairs) I'm creating a polynomial by making the keys the exponents and the associated values are the coefficients. To create an instance of this class, you enter as follows: d1 = Polynomial((5,1), (3,-4), (2,10)) which makes a dictionary like so: {2: 10, 3: -4, 5: 1} Now, I want to create a subclass of the Polynomial class called Quadratic. I want to call the

Why does it store or allocate memory for super class variables, in sub class object?

由 前提是你 提交于 2019-11-29 13:05:14
In the following code- class Mammal { String name = "furry "; String makeNoise() { return "generic noise"; } } class Zebra extends Mammal { String name = "stripes "; String makeNoise() { return "bray"; } } public class ZooKeeper { public static void main(String[] args) { new ZooKeeper().go(); } void go() { Mammal m = new Zebra(); System.out.println(m.name + m.makeNoise()); Zebra z = new Zebra(); System.out.println(z.name + z.makeNoise()); } } Both objects ( m and z ), if I see in debug windows of eclipse, contain both values of name variable ( furry and stripes ). I do understand that in

Java — Initializing superclass variables in subclasses?

由 六月ゝ 毕业季﹏ 提交于 2019-11-29 10:32:37
Okay, so, for example, let's say I have an abstract class called "Vehicle". The Vehicle class, has, among other things, a static variable called wheels, which is not initialized. What I want to do is have other subclasses extending from the Vehicle class, like "Motorcycle", and "Truck", and in these subclasses, have the wheels initialized. Code: public abstract class Vehicle { static int wheels; //number of wheels on the vehicle } But the below doesn't work: public class Motorcycle extends Vehicle { wheels = 2; } Is there a way to do this effectively? EDIT: Thank you to all the people who

Issue with a UITapGestureRecognizer

由 心不动则不痛 提交于 2019-11-29 10:24:51
I have a main viewController, it is called WelcomeViewController . I have a UIView subclass and that has some view related stuff in it. I want to add a UITapGestureRecognizer to that subclass. I only want the gesture recognizer to acknowledge taps inside that subview. How do I do that. Should I put the UITapGestureRecognizer in the subclass or should I put it in the Welcome vc. Thanks in advance. Also, I have played around with it a bunch and can't seem to figure it out. It depends on whether you want to handle the tap in your custom view object or in the view controller. If in the view, add

Subclass in type hinting

由 拈花ヽ惹草 提交于 2019-11-29 09:14:39
I want to allow type hinting using Python 3 to accept sub classes of a certain class. E.g.: class A: pass class B(A): pass class C(A): pass def process_any_subclass_type_of_A(cls: A): if cls == B: # do something elif cls == C: # do something else Now when typing the following code: process_any_subclass_type_of_A(B) I get an PyCharm IDE hint 'Expected type A, got Type[B] instead.' How can I change type hinting here to accept any subtypes of A? According to this ( https://www.python.org/dev/peps/pep-0484/#type-definition-syntax , "Expressions whose type is a subtype of a specific argument type

Possible to Subclass UILocalNotification and Change Default “Close” Button Text and Method?

由 半世苍凉 提交于 2019-11-29 09:01:52
Searching for a way to change the "Close" button text/functionality of a UILocalNotification ... I've found that it's impossible to access/call the text/function from another object, although subclassing UILocalNotification should allow implementation method overrides ... not to mention the creation of an accessor to get/set the "Close" button text field. What do you guys think about this? What would Apple? Has anyone tried?... EDIT: 12/21/2011 12:01 PM The question that I'm asking involves an understanding of oop: late/early binding, dynamic method lookup, and declared type vs. runtime type
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