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Questions tagged [self]

A keyword used in instance methods to refer to the object on which they are working.

In many object-oriented programming languages, self (also called this or Me) is a keyword that is used in instance methods to refer to the object on which they are working. Languages like and others such as , and use self. uses self or super; and languages which derive in style from it (such as , , and ) generally use this. Visual Basic uses Me.

Invoking a method on the self searches for the method implementation of the method in the usual manner, starting in the dispatch table of the receiving object’s class.

Example:

[self startThread];
self.hostReach = YES;
BOOL value = self.hostReach;

Here, self is a variable name that can be used in any number of ways, even assigned a new value.

Inside an instance method, self refers to the instance; inside a class method, self refers to the class object.

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What is the purpose of the `self` parameter? Why is it needed?

Consider this example: class MyClass: def func(self, name): self.name = name I know that self refers to the specific instance of MyClass. But why must func explicitly include self as a parameter? Why do we need to use self in the…
richzilla
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What do __init__ and self do in Python?

I'm learning the Python programming language and I've came across something I don't fully understand. In a method like: def method(self, blah): def __init__(?): .... .... What does self do? What is it meant to be? Is it…
GUIDED BOMB
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"TypeError: method() takes 1 positional argument but 2 were given" but I only passed one

If I have a class ... class MyClass: def method(arg): print(arg) ... which I use to create an object ... my_object = MyClass() ... on which I call method("foo") like so ... >>> my_object.method("foo") Traceback (most recent call…
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Why do I get "TypeError: Missing 1 required positional argument: 'self'" trying to call a method from the class directly?

I have some code like: class Pump: def __init__(self): print("init") def getPumps(self): pass p = Pump.getPumps() print(p) But I get an error like: Traceback (most recent call last): File…
DominicM
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Difference between 'cls' and 'self' in Python classes?

Why is cls sometimes used instead of self as an argument in Python classes? For example: class Person: def __init__(self, firstname, lastname): self.firstname = firstname self.lastname = lastname @classmethod def…
Scaraffe
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Why do you need explicitly have the "self" argument in a Python method?

When defining a method on a class in Python, it looks something like this: class MyClass(object): def __init__(self, x, y): self.x = x self.y = y But in some other languages, such as C#, you have a reference to the object that…
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Python decorators in classes

Can one write something like: class Test(object): def _decorator(self, foo): foo() @self._decorator def bar(self): pass This fails: self in @self is unknown I also tried: @Test._decorator(self) which also fails: Test…
hcvst
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Instance variable: self vs @

Here is some code: class Person def initialize(age) @age = age end def age @age end def age_difference_with(other_person) (self.age - other_person.age).abs end protected :age end What I want to know is the difference…
sarunw
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How to avoid explicit 'self' in Python?

I have been learning Python by following some pygame tutorials. Therein I found extensive use of the keyword self, and coming from a primarily Java background, I find that I keep forgetting to type self. For example, instead of self.rect.centerx I…
bguiz
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What does new self(); mean in PHP?

I've never seen code like this: public static function getInstance() { if ( ! isset(self::$_instance)) { self::$_instance = new self(); } return self::$_instance; } Is it the same as new className() ? EDIT If the class is…
user198729
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WPF Bind to itself

I've got a WPF Window, and somewhere there is a ListView where I bind a List to. Now somewhere in my ListView there is a TextBox and the Content property is set to {Binding}. But this is the shorthand. How do I write the full binding to…
Anemoia
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Difference between Python self and Java this

I had done a bit of Python long back. I am however moving over to Java now. I wanted to know if there were any differences between the Python "self" method and Java "this". I know that "self" is not a keyword while "this" is. And that is pretty much…
Bayko
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When to use self in Model?

Question: when do I need to use self in my models in Rails? I have a set method in one of my models. class SomeData < ActiveRecord::Base def set_active_flag(val) self.active_flag = val self.save! end end When I do this, everything works…
varatis
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Python - self, no self and cls

Yet another question on what the 'self' is for, what happens if you don't use 'self' and what's 'cls' for. I "have done my homework", I just want to make sure I got it all. self - To access an attribute of an object, you need to prefix the attribute…
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Distinction in Swift between uppercase "Self" and lowercase "self"

While playing in a Swift playground I noticed that Self, with capital "S", is available along with the lowercase self. Is there any difference between them? If so, what are usages for these two, especially for Self?
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