The self Keyword in Python

This tutorial will explain the purpose and use of the self keyword in Python. In object-oriented programming, we have classes, and each class has various attributes and methods. Whenever an object or instance of a class is created, the constructor (__init__() method in Python) is called to initialize the instance’s attributes.

While creating an instance of a class, we need to differentiate or specify the instance attributes from the arguments and other variables. And that’s where we need the self keyword to specify that we are passing the value to the instance attributes and not to the local variable or argument with the same name.

Suppose, for a class car we pass argument color to the __init__() method to initialize the color attribute of the car class, we will specify the color attribute of the instance as self.color, which shows that the class car has an attribute color and we assige the value to that attribute.

Similarly, we can also call the class’s instance methods using the self keyword like self.start() method of the car class. So in short we can say that the self keyword allows the user to specify and access the attributes and methods of an instance of the class.

Use and Example Codes of the self Keyword in Python

Now, let us look into how the self keyword is used in Python to specify an instance’s methods and attributes through the example code.

The first example code given below demonstrates how the self keyword is used in the __init__() method to initialize the attributes of the instance being initialized. We do not need to declare or create variables before initializing or assigning values to them so that we can initialize the instance attributes in the following way:

class car:

    def __init__(self, model, color):

        self.model = model
        self.color = color

mycar = car('model XYZ','red')
print(mycar.model)
print(mycar.color)

Output:

model XYZ
red

As can be seen above, the __init__() method is called automatically on creating a new instance of the class, and its attributes get initialized. The self needs to be the method’s parameter to access the instances’ methods and attributes.

The below example code demonstrates how to use the self keyword to call the instance/class methods within other class methods in Python.

class car:
    def __init__(self, model, color):

        self.model = model
        self.color = color

        self.start()

    def start(self):

        print(self.model + ", has started!")

mycar = car('model XYZ','red')

Output:

model XYZ, has started!

As in the above example code, we can call class methods using the self keyword and access the attributes in any class method by passing the instance of the class as self parameter.

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