Python 3- Deep | Dive -part 4 - Oop-

class EmployeeDiscount(DiscountStrategy): # Extension: No existing code modified def apply(self, amount: float) -> float: return amount * 0.5

from abc import ABC, abstractmethod class Bird(ABC): @abstractmethod def move(self): 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 FlyingBird(Bird): @abstractmethod def fly(self, altitude: int): pass class EmailSender(MessageSender): # Low-level def send(self

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 Scanner(Protocol): def scan(self, doc: str) -> None: ...

class EmailSender(MessageSender): # Low-level def send(self, message: str) -> None: # SMTP logic here pass