Reference library

OOP & classes

Classes, instances, methods, dataclasses, and object-oriented design in Python.

5 matches
OOP & classes easy

Compute Derived Fields with @dataclass __post_init__ in Python

Compute derived fields like distance, area, and perimeter automatically in Python dataclasses using __post_init__ and field(init=False).

dataclasses oop derived-fields
Python 
from dataclasses import dataclass, field
from math import sqrt


@dataclass
class Point:
    x: float
    y: float
    distance: float = field(init=False)

    def __post_init__(self):
        self.distance = sqrt(self.x ** 2 + self.y ** 2)


@dataclass
class Rectangle:
    width: float
    height: float
    area: flo…
12 0 Open
OOP & classes easy

How to Call a Parent Class __init__ with super() in Python

Shows how to chain __init__ calls through a class hierarchy using super(), so each class sets its own attributes while reusing the parent's initialization logic.

oop inheritance super
Python 
class Animal:
    def __init__(self, name, species):
        self.name = name
        self.species = species
        print(f"Animal init: {self.name}, {self.species}")

class Mammal(Animal):
    def __init__(self, name, species, fur_color):
        super().__init__(name, species)
        self.fur_color = fur_color
   …
13 0 Open
OOP & classes easy

How to Define a Simple Class with __init__ and __repr__ in Python

Defines a Person class with __init__ to store name and age, and __repr__ to give a readable string representation.

class oop init
Python 
class Person:
    def __init__(self, name, age):
        self.name = name
        self.age = age

    def __repr__(self):
        return f"Person(name='{self.name}', age={self.age})"


if __name__ == "__main__":
    p1 = Person("Alice", 30)
    p2 = Person("Bob", 25)
    print(p1)
    print(p2)
10 0 Open
OOP & classes easy

How to Define a Simple Python Class with __init__ and __repr__

Define a basic Python class with an __init__ method to set instance attributes and a __repr__ method for a readable representation of objects.

classes oop init
Python 
class Person:
    def __init__(self, name, age):
        self.name = name
        self.age = age

    def __repr__(self):
        return f"Person(name={self.name!r}, age={self.age!r})"


if __name__ == "__main__":
    person = Person("Alice", 30)
    print(person)
15 0 Open
OOP & classes easy

Validate dataclass fields with __post_init__ in Python

Add custom validation to a Python dataclass inside __post_init__, raising ValueError or TypeError for invalid field values.

dataclasses validation post-init
Python 
from dataclasses import dataclass, field
from typing import Optional


@dataclass
class Product:
    name: str
    price: float
    quantity: int = 1
    category: Optional[str] = None

    def __post_init__(self):
        if not self.name or not isinstance(self.name, str):
            raise ValueError("name must be a…
11 0 Open

Browse by section

Each section groups closely related Python snippets.

OOP & classes — Python code examples

What you will find here

This page collects oop & classes snippets — short, copy-ready Python you can paste into our free online IDE and run without installing anything. Each sample includes a plain-English explanation and the full source code.

Samples vs tutorials and challenges

Samples are quick reference — one concept per page. For step-by-step teaching, use our Python tutorials. To test yourself, try quizzes or coding challenges. Clean up style with the Python formatter.

Related coding tools

Free online Python IDE Write and run Python in your browser — no install. Free Python code formatter Format with autopep8 — side-by-side PEP 8 cleanup. Python code samples Copy-ready snippets to study and run in the IDE.