SOLID原則とは？初心者でもわかるオブジェクト指向設計の基本5原則【Python実例付き】

class UserManager:
    def register(self, name, email):
        # ユーザー登録
        pass

    def send_welcome_email(self, email):
        # メール送信
        pass

    def save_to_database(self, user):
        # DB保存
        pass

    def generate_monthly_report(self):
        # レポート生成
        pass

    def validate_input(self, data):
        # 入力検証
        pass

class User:
    def __init__(self, name, email):
        self.name = name
        self.email = email

    def save(self):
        # DBに保存（DB責任）
        pass

    def send_email(self, subject, body):
        # メール送信（通知責任）
        pass

    def calculate_age(self, birthdate):
        # 年齢計算（ビジネスロジック責任）
        pass

class User:
    def __init__(self, name, email):
        self.name = name
        self.email = email

class UserRepository:
    def save(self, user: User):
        # DBに保存
        pass

class EmailService:
    def send(self, to: str, subject: str, body: str):
        # メール送信
        pass

class AgeCalculator:
    def calculate(self, birthdate) -> int:
        # 年齢計算
        pass

class DiscountCalculator:
    def calculate(self, customer_type: str, price: float) -> float:
        if customer_type == "normal":
            return price * 0.9
        elif customer_type == "vip":
            return price * 0.8
        elif customer_type == "super_vip":
            return price * 0.7
        # 新しい顧客タイプ追加のたびにここを修正...

from abc import ABC, abstractmethod

class Discount(ABC):
    @abstractmethod
    def calculate(self, price: float) -> float:
        pass

class NormalDiscount(Discount):
    def calculate(self, price: float) -> float:
        return price * 0.9

class VipDiscount(Discount):
    def calculate(self, price: float) -> float:
        return price * 0.8

# 新しい割引タイプを追加（既存コード修正なし）
class SuperVipDiscount(Discount):
    def calculate(self, price: float) -> float:
        return price * 0.7

class Bird:
    def fly(self):
        return "Flying!"

class Penguin(Bird):
    def fly(self):
        raise Exception("Penguins can't fly!")

# 利用側のコードが壊れる
def make_bird_fly(bird: Bird):
    return bird.fly()  # Penguinが渡されると例外発生

class Bird:
    def eat(self):
        return "Eating!"

class FlyingBird(Bird):
    def fly(self):
        return "Flying!"

class Penguin(Bird):
    def swim(self):
        return "Swimming!"

class Eagle(FlyingBird):
    pass

# 安全：FlyingBirdだけにflyを要求
def make_bird_fly(bird: FlyingBird):
    return bird.fly()

from abc import ABC, abstractmethod

class Worker(ABC):
    @abstractmethod
    def work(self):
        pass

    @abstractmethod
    def eat(self):
        pass

    @abstractmethod
    def sleep(self):
        pass

class Robot(Worker):
    def work(self):
        return "Working!"

    def eat(self):
        raise NotImplementedError("Robots don't eat")

    def sleep(self):
        raise NotImplementedError("Robots don't sleep")

from abc import ABC, abstractmethod

class Workable(ABC):
    @abstractmethod
    def work(self):
        pass

class Eatable(ABC):
    @abstractmethod
    def eat(self):
        pass

class Sleepable(ABC):
    @abstractmethod
    def sleep(self):
        pass

class Human(Workable, Eatable, Sleepable):
    def work(self):
        return "Working!"
    def eat(self):
        return "Eating!"
    def sleep(self):
        return "Sleeping!"

class Robot(Workable):
    def work(self):
        return "Working!"

class MySQLDatabase:
    def save(self, data):
        # MySQLに保存
        pass

class UserService:
    def __init__(self):
        self.db = MySQLDatabase()  # 具体実装に直接依存

    def create_user(self, name):
        self.db.save({"name": name})

from abc import ABC, abstractmethod

class Database(ABC):
    @abstractmethod
    def save(self, data):
        pass

class MySQLDatabase(Database):
    def save(self, data):
        # MySQLに保存
        pass

class PostgreSQLDatabase(Database):
    def save(self, data):
        # PostgreSQLに保存
        pass

class UserService:
    def __init__(self, db: Database):  # 抽象に依存
        self.db = db

    def create_user(self, name):
        self.db.save({"name": name})

# 使用例
service = UserService(MySQLDatabase())
# DB変更も簡単
service = UserService(PostgreSQLDatabase())