What is the purpose of self?

Question

What is the purpose of the `self` word in Python? I understand it refers to the specific object created from that class, but I can't see why it explicitly needs to be added to every function as a parameter. To illustrate, in Ruby I can do this: class myClass def myFunc(name) @name = name end endWhich I understand, quite easily. However in Python I need to include `self`: class myClass: def myFunc(self, name): self.name = nameCan anyone talk me through this? It is not something I've come across in my (admittedly limited) experience.

Answer 1

I asked the same question when I first started learning Python, and that was when I

had considerable coding experience, so I understand the confusion.

Other OO languages like C++ and Java have an omnipresent reference called "this",

which always refers to "the current object", but DOESN'T need to be explicitly

defined in every method signature.

So if we're implementing a method that needs to reference a data or method member of that

object, "this" would be used to fully qualify that reference.

For example in Java, if we needed to assign 128 to an int data member called 'x',

we would code as follows:

this.x = 128;

Using "this" to fully qualify 'x' above might be required to differentiate it from

another variable/reference 'x' declared in local scope, OR "this" might be used

optionally just to highlight that 'x' is a member of the current object.

In Python, "self" is essentially equivalent to "this" in C++/Java,

except that the Python architects decided to be more explicit

about what's going on here.

When an object method/function is invoked, the instance itself

is transparently passed in as the 1st attribute.

See partial example of a "Calculator" class below (limited to

addition and subtraction).

"self" needs to be defined as the 1st argument in every method ....

class Calculator(object):

__value__ = 0

__valueHistory__ = []

def add(self, number):

self.__valueHistory__.append(self.__value__)

self.__value__ += number

def sub(self, number):

self.__valueHistory__.append(self.__value__)

self.__value__ -= number

... but when we use an instance of Calculator and invoke its methods,

"self" is not included in the method signature.

## Create an instance of the Calculator Class

calc = Calculator()

## add 5 to the calc (5)

calc.add(5)

## subtract 2 from the calc (3)

calc.sub(2)

I have read through many explanations of the "self" reference in Python.

What it is and how it works is quite clear, but why Python language

designers forced its declaration in every object method is not explained beyond,

"Explicit is better than implicit".

One of the better overviews of this topic appears here -> www.programiz.com/article/python-self-why

Clearly, the language could have not mandated its inclusion in every method signature ....