Introduction

This is a comprehensive tutorial for Python beginners on object-oriented programming, the objective of this tutorial is to give you an insight into object-oriented programming and help you understand its basics through practical examples.
In this tutorial, we will cover the following concepts :

• What is OOP?

• Class vs Object.

• Attributes vs Methods.

• Inheritance

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Requirements

• Basic python understanding.

• A text editor and python installed.

What Is Object-Oriented Programming in Python?

Object-oriented programming is an approach to modeling real-world elements, such as players in a game or employees in a company. A simple example of an object is a car with properties such as color, speed, brand and weight, and methods such as increase or decrease speed, stop, turn right or left, reverse...
An object has basically two characteristics:

• attributes

• behavior

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Class and Object

We can define a class as a blueprint for the object. We can think of it as a sketch of a car containing all the details about the car. When class is defined, only the description for the object is defined. Therefore, no memory or storage is allocated. Meanwhile, an object (instance) is an instantiation of a class, an object is a car with red color for example and 300km/h as maximum speed.
Here I have created a simple visualization of the difference between a class and an object:

If the concept of OOP is not yet clear in your mind, don't worry! The following practical example will make it easier for you.

OOP In python

Attributes

The attributes are a characteristic of an object.
Let's take the previous example and define a class in python called Car, to define a class in python we use the class keyword as follows:

class Car:
    pass

Now let's define our class with some attributes :

class Car:
    def __init__(self, color, brand, maxSpeed):
        self.color = color 
        self.brand = brand
        self.maxSpeed = maxSpeed

The init function the initializer method and it is called when an object is instantiated, for example if we want to create two cars, each with specific properties, we will create two objects of the previous class, one called car1 and the other car2 for example :

car1 = Car('red', 'audi', 300)
car2 = Car("blue", "BMW", 120)

Now, if we want to get an attribute of an object, we will simply type :

print(car1.color)

then, we will get red as output.

Methods

Methods are functions defined inside the body of a class. They are used to define the behaviors of an object.
Now, let's define a method called changeMaxSpeed():

class Car:
    def __init__(self, color, brand, maxSpeed):
        self.color = color 
        self.brand = brand
        self.maxSpeed = maxSpeed

    def changeMaxSpeed(self, newMaxSpeed):
        self.maxSpeed = newMaxSpeed

This function takes two parameters, self which points to the instantiated object, and newMaxSpeed the new maximum speed value.

• Note :

A method must have an extra first parameter in the method definition usually called "self". We do not give a value for this parameter when we call the method, Python provides it If we have a method that takes no arguments, then we still have to have one argument. This is similar to this pointer in C++ and this reference in Java.

Now let's instantiate a car with a maximum speed of 200 and modify it with our method :

car1 = Car('red', 'audi', 200)
car1.changeMaxSpeed(300)

Here, car1 plays the role of self, so it is not necessary to specify it, if you specify it, it will give you an error saying that it was expecting one parameter but two were given.

Inheritance

To understand the concept of inheritance, we will take a simple example, Imagine we have a class called vehicle and our previous class called car, when we first created the class vehicle as follows :

class Vehicle:
    def __init__(self, color, maxSpeed):
        self.color = color 
        self.maxSpeed = maxSpeed

    def changeMaxSpeed(self, newMaxSpeed):
        self.maxSpeed = newMaxSpeed

    def changeColor(self, newColor):
        self.color = newColor

Now when we will create the class Car, we want our class to inherit from the previous class, meaning that we dont want to define the previous attributes and methods again.

class Car(Vehicle):
   def __init__(self, color, maxSpeed, brand):
      self.brand = brand

Now, we can access the variables and methods of the parent class
So basically, Inheritance is the capability of one class to derive or inherit the properties from another class. The class that derives properties is called the child class and the class from which the properties are being derived is called the parent class.

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