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Python Classes/Objects · Examples
Object-Oriented Python

Python Classes/Objects Examples

Short, runnable programs that show python classes and objects in action. Read the explanation, press Run, then change the code and try your own ideas. New to the topic? Start with the Python Classes and Objects lesson.

1A method that protects the data

Methods can check a request before changing an attribute. Here spend refuses to take more cash than the wallet holds and returns whether it worked.

A method that protects the data 
class Wallet:
    def __init__(self, cash):
        self.cash = cash

    def spend(self, amount):
        if amount > self.cash:
            return False
        self.cash -= amount
        return True

wallet = Wallet(20)
print(wallet.spend(15), wallet.cash)
print(wallet.spend(15), wallet.cash)
Expected outputTrue 5
False 5

2Class attributes vs instance attributes

school and count live on the class and are shared. name is set on self, so each student has their own.

Class attributes vs instance attributes 
class Student:
    school = "Hillside High"
    count = 0

    def __init__(self, name):
        self.name = name
        Student.count += 1

a = Student("Asha")
b = Student("Ben")
print(a.name, "|", b.name)
print(a.school, "|", b.school)
print("Students created:", Student.count)
Expected outputAsha | Ben
Hillside High | Hillside High
Students created: 2

3__str__ for people, __repr__ for programmers

print() uses __str__. A list shows its items with __repr__, and f-strings can ask for it with !r.

__str__ for people, __repr__ for programmers 
class Point:
    def __init__(self, x, y):
        self.x = x
        self.y = y

    def __str__(self):
        return f"({self.x}, {self.y})"

    def __repr__(self):
        return f"Point(x={self.x}, y={self.y})"

p = Point(2, 5)
print(p)
print([p, Point(0, 0)])
print(f"Debug: {p!r}")
Expected output(2, 5)
[Point(x=2, y=5), Point(x=0, y=0)]
Debug: Point(x=2, y=5)

4A list of objects

Objects fit anywhere other values do. Each Item knows how to calculate its own total, so the loop stays simple.

A list of objects 
class Item:
    def __init__(self, name, price, qty):
        self.name = name
        self.price = price
        self.qty = qty

    def total(self):
        return self.price * self.qty

cart = [Item("pen", 1.5, 4), Item("notebook", 3.25, 2), Item("bag", 24.0, 1)]
for item in cart:
    print(f"{item.name:<10}{item.total():>6.2f}")
print("Grand total:", sum(item.total() for item in cart))
Expected outputpen         6.00
notebook    6.50
bag        24.00
Grand total: 36.5

Practise next

Python Classes and Objects exercises → Back to the lesson

Python Class Attributes vs Instance Attributes examplesPython Encapsulation: Public, Protected and Private examplesPython Dunder (Magic) Methods examples