Python Classes, Objects and OOP concepts

Classes Objects in Python

All modern day programming languages are based on the concept of OOP – object oriented programming and support classes and objects. Python too is an object oriented language right from the very beginning. Let’s have a look at the basics of object oriented programming. An object is creating or encapsulating your customized group of variables that has its own set of attributes, functions and properties. A call defines all the characteristics and properties of an object. The object can access methods with the help of dot notation. A variable that holds data values associated with a class and its objects is known as data member.

OOP Classes, Sub Classes and Objects
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Following are some more terms that you would need to know  about Python classes/objects:
1. A variable that is defined inside a method of a class and can be accessed only by the instance of that class are called instance variable.
2. If you derive a class from another class such that it has all the characteristics of the parent class is called Inheritance.
3. An object of a class is also known as an instance.
4. When you create an instance of a class it is called instantiation.
5. A function that is part of class definition is known as a method

The syntax for defining a class is as follows:

class Class_Name:

The syntax for creating an object is:

object_name = Class_Name()

Now let’s try to understand how a class works with the help of a simple example:

class Hello_World:
    def hello_world(self,x):
        self.x = x

obj_hellow = Hello_World()
obj_hellow.hello_world("Hello World")    

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Python self keyword

In Python, in every function, the first argument refers to its current instance and this argument is the self. Notice this in the code above. When we make a call to a function we don’t pass any value for self.

If there is a need to customize an object to an initial state when it is created then you will have to define an __init__() function in the class. Look at the following piece of code:

class Hello_World:
    def __init__ (self, x):
        self.x = x
obj_hellow = Hello_World("Hello World")

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So, here you can see when you create the object, a string value “Hello World” is passed as an argument. The __init__() function assigns this value to the attribute x. So, to access this value you can access the variable with a dot notation obj_hellow.x.

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