What are `self` and `__init__` in Python Object-Oriented Programming?

Understanding init and self in Python OOP

When learning object-oriented programming (OOP) in Python, one may encounter the init method and the self variable. These concepts play a crucial role in class definitions and object instantiation.

What is self?

In Python OOP, self is a special variable that represents an instance of the class. It is conventionally used as the first parameter of instance methods and functions, as seen in the example:

def method(self, blah):
    # ...

The self variable is a reference to the current instance of the class. It allows access to the instance's attributes and methods within the method. Without explicitly declaring self, the method would only accept one argument instead of two.

What is __init__?

The init method is a special method that serves as the constructor for a class. It is called automatically when an object of that class is created. Its purpose is to initialize the instance's attributes and set up any necessary class properties.

For example:

class A(object):
    def __init__(self):
        self.x = 'Hello'

    def method_a(self, foo):
        print(self.x + ' ' + foo)

In this example, the init method initializes the instance attribute x with the value 'Hello'. The method_a method then prints the value of x concatenated with the foo parameter.

Necessity of init and self

Both init and self are essential components of OOP in Python. They allow objects to have state (attributes) and methods that operate on that state. Without self, it would be impossible to access instance-specific attributes and methods within methods. Similarly, without the init method, it would not be possible to initialize instance attributes when an object is created.

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