Python by Example: Classes

Classes are blueprints for creating objects. They bundle data (attributes) and behavior (methods) together. Use them when you have data that belongs together and functions that operate on it. The __init__ method runs when you create an instance; self refers to the instance.

What you'll learn:

• Defining a class with class
• The __init__ constructor
• Instance attributes and the self parameter
• Creating instances by calling the class

class Dog:
    def __init__(self, name, age):
        self.name = name
        self.age = age

    def bark(self):
        return f"{self.name} says woof!"


dog = Dog("Rex", 3)
print(dog.name)
print(dog.age)
print(dog.bark())

Dog("Rex", 3) creates a new Dog; Python calls __init__(self, "Rex", 3). self.name and self.age store data on the instance. Every instance method takes self as the first parameter.

To run this program:

$ python source/classes.py
Rex
3
Rex says woof!

Tip: Class names use PascalCase (e.g., Dog, UserAccount). Method and attribute names use snake_case (e.g., bark, user_name).

Try it: Add a method that returns the dog's age in "dog years" (age * 7).

Source: classes.py

Next: Methods