Python - OOP Basics

Overview

Estimated time: 35–45 minutes

Define classes, use instance/class/static methods, create computed attributes with @property, and simplify data containers with dataclasses.

Learning Objectives

• Define a simple class with methods and attributes.
• Use @property for validation/computed values.
• Create lightweight data containers with @dataclass.

Prerequisites

• Python - Errors & Exceptions

Classes and methods

class Counter:
    def __init__(self, start=0):
        self.value = start
    def inc(self):
        self.value += 1

c = Counter()
c.inc()
print(c.value)

Expected Output: 1

@property

class Person:
    def __init__(self, first, last):
        self.first = first
        self.last = last
    @property
    def full_name(self):
        return f"{self.first} {self.last}"

p = Person("Ann", "Lee")
print(p.full_name)

Expected Output: Ann Lee

Dataclasses

from dataclasses import dataclass

@dataclass
class Point:
    x: int
    y: int

pt = Point(3, 4)
print(pt)

Expected Output: Point(x=3, y=4)

Common Pitfalls

• Forgetting self in instance method definitions.
• Mutating shared class attributes when you meant instance attributes.

Checks for Understanding

1. What is @property used for?
2. How does @dataclass help compared to writing __init__ manually?

Exercises

1. Create a Rectangle class with width/height and an area @property.
2. Make a dataclass for a Task with title and done flag; print friendly text.