Lesson 2

Exploring Class Attributes and Methods in Python

Course Overview and Lesson Goal

Hello, Explorer! Today, we're delving into the realm of Python's Object-Oriented Programming (OOP), focusing on class attributes and methods. Our goal is to grasp these concepts using clear, practical examples. Let's get started!

Introduction to Class Attributes

Class attributes are properties of class instances. For instance, a Spaceship class could include attributes such as color, max speed, and fuel capacity. These are defined within the class block, as shown below:

Python
1class Spaceship: 2 color = "white" 3 max_speed = 10000 4 fuel_capacity = 20000

These attributes can be accessed through a class instance, like so:

Python
1enterprise = Spaceship() 2print(enterprise.color) # prints: white 3print(enterprise.max_speed) # prints: 10000
Methods in Action

Class methods define a class's behavior. For example, a spaceship can fly. Methods are essentially functions within a class. The fly method below enables an instance of the Spaceship class to fly:

Python
1class Spaceship: 2 color = "white" 3 fuel_capacity = 20000 4 5 def fly(self, speed): 6 return f"The {self.color} spaceship is flying! Speed = {speed}, fuel_capacity = {self.fuel_capacity}"

Note, that when referring to class attributes inside the class, you should always use the self keyword that's always provided as a first parameter in every method of the class, similarly to how we used self.color, and self.fuel_capacity in the example above. At the same time, the provided parameter speed is just used as is, as it's not a class attribute but an external parameter.

This fly method can be invoked in the following manner:

Python
1enterprise = Spaceship() 2print(enterprise.fly(10000)) # prints: The white spaceship is flying! Speed = 10000, fuel_capacity = 20000
Interacting with Class Attributes and Methods

Attributes and methods can be accessed and implemented through class instances. The attributes of a class can be set, and its methods can be called, as demonstrated below:

Python
1enterprise = Spaceship() 2enterprise.color = "blue" # setting an attribute 3enterprise.fly() # calling a method
Interactions between Classes

Different classes can interact with each other:

Python
1class Star: 2 brightness = 5 3 4 def shine(self): 5 return self.brightness 6 7class Planet: 8 star = Star() 9 10 def get_light(self): 11 return self.star.shine() 12 13earth = Planet() 14print(earth.get_light()) # Prints: 5

See how the Planet class created an attribute that is an instance of the Star class and how we then use it in the get_light() method in the Planet class.

Constants: A Special Kind of Class Attributes

Constants are class attributes that remain unchanged. They are typically declared in capitalized letters, as follows:

Python
1class Physics: 2 UNIVERSAL_GRAVITATIONAL_CONSTANT = 6.6743 * 10**(-11)

In this case, the UNIVERSAL_GRAVITATIONAL_CONSTANT constant doesn't vary across instances of the Physics class.

Lesson Summary

Congratulations! You now understand class attributes and methods. Continue exploring and anticipate our next Python adventure: the study of the __init__ method, inheritance, and more!

Today, we unraveled the details of class attributes and methods in Python. You've learned how to define them and bring Python objects to life. A hands-on exercise follows next. Remember, practice is the key to mastering these concepts. Happy coding!

Enjoy this lesson? Now it's time to practice with Cosmo!

Practice is how you turn knowledge into actual skills.