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 EmailSender(MessageSender): # Low-level def send(self, message: str) -> None: # SMTP logic here pass Python 3- Deep Dive -Part 4 - OOP-
class Sparrow(FlyingBird): def move(self): return self.fly(100) def fly(self, altitude: int): return f"Flying at altitude" Deep Dive Issue: Python is not statically typed
from abc import ABC, abstractmethod class MessageSender(ABC): # Abstraction @abstractmethod def send(self, message: str) -> None: pass doc): raise NotImplementedError
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() .
from abc import ABC, abstractmethod class DiscountStrategy(ABC): @abstractmethod def apply(self, amount: float) -> float: pass
class MultiFunctionDevice(ABC): @abstractmethod def print(self, doc): pass @abstractmethod def scan(self, doc): pass @abstractmethod def fax(self, doc): pass class SimplePrinter(MultiFunctionDevice): def print(self, doc): ... def scan(self, doc): raise NotImplementedError # Forced dependency def fax(self, doc): raise NotImplementedError