OOP & classes
Classes, instances, methods, dataclasses, and object-oriented design in Python.
How to Sort Data in Python with a Class Helper
This beginner-friendly class wraps the built-in sorted() function to sort numbers, strings ignoring case, and dictionaries by a specified key.
class DataSorter:
def __init__(self, data):
self.data = data
def sort_numbers(self, reverse=False):
return sorted(self.data, reverse=reverse)
def sort_strings_ignore_case(self, reverse=False):
return sorted(self.data, key=str.lower, reverse=reverse)
def sort_dicts_by_key(self…How to Use IntEnum Arithmetic for Priority Levels in Python
Demonstrates Python IntEnum arithmetic for priority levels, showing how enum members behave like integers in calculations and comparisons.
from enum import IntEnum
class Priority(IntEnum):
LOW = 1
MEDIUM = 5
HIGH = 10
CRITICAL = 20
if __name__ == "__main__":
current = Priority.MEDIUM
boosted = current + 3
lowered = current - 2
doubled = current * 2
print(f"Current: {current} ({current.value})")
print(f"Boosted (…How to Validate Data Types in Python with a Class
A beginner-friendly Python class that checks if a value is a string, integer, float, list, or empty, using simple methods and isinstance checks.
class DataValidator:
"""A simple data validation helper for beginners."""
def __init__(self, data):
self.data = data
def is_string(self):
return isinstance(self.data, str)
def is_integer(self):
return isinstance(self.data, int) and not isinstance(self.data, bool)
…How to Validate User Input with a Dataclass in Python
A dataclass stores name, age, and email, and a validator class checks each field, returning a dictionary of boolean results.
from dataclasses import dataclass
@dataclass
class UserInput:
name: str
age: int
email: str
def is_valid_name(self) -> bool:
return bool(self.name.strip()) and len(self.name.strip()) >= 2
def is_valid_age(self) -> bool:
return isinstance(self.age, int) and 0 < self.age < 150
…How to define a custom exception class in Python with an error code attribute
Create a custom exception class with extra attributes like an error code, then raise and catch it in a try/except block.
class UserNotFoundError(Exception):
def __init__(self, user_id, error_code=404):
self.user_id = user_id
self.error_code = error_code
super().__init__(f"User with ID {user_id} was not found (error code: {error_code})")
def find_user(user_id, users_db):
if user_id not in users_db:
…How to merge dictionaries by a key in Python with a class
This code defines a DataMerger class that collects dictionary records and merges them by a specified key, combining fields from multiple records with the same key.
class DataMerger:
def __init__(self):
self.records = []
def add_record(self, record):
if isinstance(record, dict):
self.records.append(record)
else:
raise TypeError("Record must be a dictionary")
def merge_by_key(self, key):
merged = {}
for …Parse CSV Data with a Python Class
Encapsulate CSV file loading and column/row access methods in a reusable DataParser class for beginners.
class DataParser:
def __init__(self, file_path):
self.file_path = file_path
self.data = []
def load_data(self):
with open(self.file_path, 'r') as file:
for line in file:
row = line.strip().split(',')
self.data.append(row)
return self.…Slots Class: How to Reduce Memory Usage in Python
Use __slots__ to prevent dynamic attribute creation and reduce per-instance memory overhead, while keeping methods intact.
class SlotsDemo:
__slots__ = ("name", "age", "email")
def __init__(self, name, age, email):
self.name = name
self.age = age
self.email = email
def describe(self):
return f"{self.name}, {self.age}, {self.email}"
if __name__ == "__main__":
instance = SlotsDemo("Alice", …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.
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…Browse by section
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OOP & classes — Python code examples
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