Python 3- Deep Dive -part 4 - Oop- ◎

from dataclasses import dataclass @dataclass class Employee: name: str salary: float Responsibility 2: Business logic class PayCalculator: def calculate(self, emp: Employee) -> float: return emp.salary * 0.8 Responsibility 3: Persistence class EmployeeRepository: def save(self, emp: Employee) -> None: # Uses SQLAlchemy, filesystem, etc. pass 2. O: Open/Closed Principle (OCP) Classes should be open for extension, but closed for modification. Deep Dive Issue: Python is not statically typed. Without ABC or Protocol , developers often write long if/elif chains checking type() .

class EmailSender(MessageSender): # Low-level def send(self, message: str) -> None: # SMTP logic here pass Python 3- Deep Dive -Part 4 - OOP-

class Bird: def fly(self, altitude: int) -> None: return f"Flying at altitude" class Penguin(Bird): def fly(self, altitude: int) -> None: # Violation: Changes pre-condition (cannot fly) raise NotImplementedError("Penguins can't fly") Deep Dive Issue: Python is not statically typed

class StandardDiscount(DiscountStrategy): def apply(self, amount: float) -> float: return amount * 0.9 from abc import ABC

Here is a deep technical breakdown of applying principles in advanced Python OOP. 1. S: Single Responsibility Principle (SRP) A class should have only one reason to change. Deep Dive Issue: In Python, it's tempting to add save() , load() , or generate_report() methods directly into a data class because of how easy dynamic attributes are.

from abc import ABC, abstractmethod class Bird(ABC): @abstractmethod def move(self): pass