Classes, Modeling the World

Bundle data and behaviour together with class, __init__, and self

How would you approach this? Think first, then expand.

A class is a blueprint for creating objects. An object is an instance of a class, the actual thing built from the blueprint.
Think of a class as a cookie cutter, and objects as the cookies.

Your first classpython

class Dog:
    def __init__(self, name, breed):
        self.name = name    # instance variable
        self.breed = breed

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

    def describe(self):
        return f"{self.name} is a {self.breed}"

# Create instances (objects)
fido = Dog("Fido", "Labrador")
rex = Dog("Rex", "German Shepherd")

print(fido.bark())       # Fido says: Woof!
print(rex.describe())    # Rex is a German Shepherd

`self` is a reference to the current instance. Every method gets it as the first parameter automatically. When you call fido.bark(), Python passes fido as self.

A real-world class: Serverpython

class Server:
    def __init__(self, ip, role):
        self.ip = ip
        self.role = role
        self.is_healthy = True
        self.cpu_usage = 0

    def check_health(self):
        if self.cpu_usage > 90:
            self.is_healthy = False
            return f"ALERT: {self.ip} CPU critical ({self.cpu_usage}%)"
        return f"{self.ip} OK ({self.cpu_usage}% CPU)"

    def set_cpu(self, pct):
        self.cpu_usage = pct

web1 = Server("10.0.0.1", "web")
web1.set_cpu(95)
print(web1.check_health())   # ALERT: 10.0.0.1 CPU critical (95%)

🌍In the Real World...

The Kubernetes Python client uses classes for every resource: Pod, Deployment, Service. boto3 uses classes for EC2Instance, S3Bucket, RDSInstance. Understanding classes lets you use any Python SDK properly.

Practice Exercises

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Exercise 1 of 2mediumGuided

⏱ 00:00

Build a BankAccount Class

Create a BankAccount class with:- __init__(self, owner, balance=0)- deposit(self, amount), adds to balance- withdraw(self, amount), subtracts, but print "Insufficient funds" if not enough- get_balance(self), returns current balance
Expected output:Balance: 150Balance: 100Insufficient funds

solution.py

1 / 2

Exercise 2 of 2easy

⏱ 00:00

Inventory Item

Create an InventoryItem class with name, price, quantity. Add a total_value() method.
Expected output:Widget: 3 x £9.99 = £29.97

solution.py

2 / 2

Solve all 2 exercises to unlock completion

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