- Object Oriented Programming -

In OOP, we can represent an entity using a class.

 A class bundles data (features/properties of entity - color, height, width) and functionality (movement, expression) together.

 An instance of a class is known as an object. 

Which is the only cartoon series that had predicted that Trump would be elected as the president of the USA and also predicted the coronavirus spread? 

 Answer: Simpsons. 

Simpsons is a very popular animated show. You can build something similar with python. 

But have you ever wondered, how Simpsons look the same in all the series? Only his movement looking and, expression change but his main features like color, height, and face look exactly the same all the time.

 This is because we create a ‘blueprint’ of Simpsons and whenever we have to simulate him on screen we use this blueprint. This keeps a record of all the features of Simpsons and recreates it whenever we want. 

This is where Object-Oriented Programming(OOP) helps us.

For eg: 

1. You have a class Rectangle whose

        a. properties are length, width, color, thickness and 

        b. functionalities are the draw, move.

2. You create 2 objects r1 and r2. 

         Here r1 and r2 are instances of Rectangle. 

3. Both r1 and r2 can assign different values to their properties. But their functionality (method) like how they are drawn or how they move will be the same. 

Features of class 

● Class acts as a blueprint to create complex entities. 

● Objects are real-world instances of a class.

 ● Property/Attribute values of objects can vary. 

● Methods/Functionalities applicable to objects remain the same.

 Syntax To create an object:-

 < object_name > =< class_name >(arguments) 

eg:- r1=Rectangle()

 Note: <rguments> are optional 

To access a property/method of a class we use a ‘.’ operator.

Syntax- <object_name>.<property/method_name>

eg:-

r1.height 

r1.draw() 

Let us see more about these classes and objects, using the library pygame. 

Pygame:

 Pygame is a library that helps us in python graphics i.e. draw shapes, patterns, make games, etc.

 Pixels and coordinates

 A display window can be divided into many small squares called pixels. So if we say length=50, it means 50 pixels on the screen. 

Each point on the screen is referenced by a pair (x,y) known as coordinates. 

x represents the horizontal position and y represents the vertical position. 

For eg:- 

The point (1,3) and (2,1)on the screen can be represented as :

Setup pygame display. 

Note: 500,500 specifies the [width, height] of the screen 

Draw rectangles of different sizes, different colors, and different locations.

 

Explanation: 

Here we are creating 3 instances of the rectangle. 

In first one , top left corner is (50,20) ,length is 120 ,height is 100 and color is RED

In second  one, toptheto thto the toe  left corner is (100,6), the length is 200, is 250 and the color is GREEN 

In ththirdirdthe  one, the top left corner is (150,100), the length is 40, the height is 50 and the color is BLUE 

The properties here are color, length, height, and coordinates of the top left corner. 

The method draw() is used to draw the rectangle instance. 

Method ‘rect()’ creates an instance of class Rect (a class name for Rectangle in pygame) and returns it.

Note: Different instances(objects) of rectangle look different with different properties, but ultimately they are similar in structure / how they are drawn. Output.

How to Install pygame

 Go to the terminal and give the command.

 windows

 pip3 install pygame 

Mac

 python3 -m pip install pygame --pre --user 

ChromeOS/Linux 

sudo pip3 install pygame