import smtplib # Concrete low-level class NotificationService: # High-level def alert(self, message): # Direct dependency on SMTP implementation server = smtplib.SMTP("smtp.gmail.com") server.sendmail(...)
class Penguin(Bird): def move(self): return "Swimming" # No fly method. Substitutable for Bird. Clients should not be forced to depend on methods they do not use. Deep Dive Issue: Python has no explicit interface keyword. We use Protocol (PEP 544) or multiple ABCs . Fat protocols lead to NotImplementedError stubs.
class VIPDiscount(DiscountStrategy): def apply(self, amount: float) -> float: return amount * 0.8
def generate_pdf_report(self): print(f"PDF: self.name") # Presentation 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 MessageSender(ABC): # Abstraction @abstractmethod def send(self, message: str) -> None: pass
class StandardDiscount(DiscountStrategy): def apply(self, amount: float) -> float: return amount * 0.9 Deep Dive Issue: Python has no explicit interface keyword
class Scanner(Protocol): def scan(self, doc: str) -> None: ...
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.
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") it's tempting to add save()
from abc import ABC, abstractmethod class Bird(ABC): @abstractmethod def move(self): pass
from typing import Protocol class Printer(Protocol): def print(self, doc: str) -> None: ...
def save_to_db(self): print(f"Saving self.name to DB") # Persistence