Lesson 3: Object Oriented Programming

Day 5

Overview

This self-study guide will cover how to use object oriented programming. This will include making classes, constructors and methods inside classes, along with calling these functions. This lesson will assume you have a working Python environment using Python (3.10.12) or later, though you only need version 3.0.0 to follow most of the course

Classes

Classes can represent any object that has properties and/or functions. For example a car has properties of the number of wheels, the length width, etc... Classes can also include subclasses such as a wheel for the example of a car.>

Declaration

To declare a class use the class keyword follow by the name of the class. Like functions the contents of the class MUST be indented

class Car:

Fields and Constructor

The fields of the class are variables that the class needs such as wheels or length in the previous example. Constructors are a function that is called when the class is initialized. This can include setting default values or setting values from the user.

In python a constructor MUST be called "__init__"

Heres an example of a field and constructor.

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

Note that the first argument is self representing the object that is created

Day 6

As said before classes can have functions that can modify that data or perform another task. As an example of a car we can repair it increasing the integrity

class Car:
    __init__(self, brand, color, integrity):
      self.brand = brand
      self.color = color
      self.integrity = integrity
    repair(self):
        if (self.integrity > 80):
            self.integrity = 100
        else:
            self.integrity += 20

This will increase the cars integrity by 20% when called

Create an object

To create an object of the class you can just initialize a variable of the class

car1 = Car("Toyota", "red", 99)

This will create a red toyota with 99% integrity

Create a class plan which represents the properties of a plane such as length, capacity, color, maker etc... Make sure you add a constructor and some functions such as fly and land

Challenge

Create a Student Class that represents a student. These should be the fields

grade
name
age
gpa
teachers (array of strings)

and should have these functions

# Modify the students GPA based on the grade and weight of the test in decimal 50% -> (0.5)
def test (grade, weight):
  # Changes the GPA

def attend_class(number):
  # Prints attending class period: number