Pythonでオブジェクト指向を学ぶ！クラスとインスタンスの基本をマスターしよう

class Dog:
    # 属性（変数）
    species = "Canine"

    # メソッド（関数）
    def __init__(self, name, age):
        self.name = name  # インスタンス変数
        self.age = age    # インスタンス変数

    def speak(self):
        return f"{self.name} says Woof!"

my_dog = Dog("Rex", 5)  # インスタンス化
print(my_dog.name)  # "Rex"
print(my_dog.age)   # 5
print(my_dog.speak())  # "Rex says Woof!"

class Cat:
    def __init__(self, name, color):
        self.name = name
        self.color = color

    def introduce(self):
        return f"I am {self.name} and I am {self.color}."

my_cat = Cat("Whiskers", "white")
print(my_cat.introduce())  # "I am Whiskers and I am white."

class Person:
    population = 0  # クラス変数

    def __init__(self, name):
        self.name = name
        Person.population += 1  # クラス変数を更新

    @classmethod
    def get_population(cls):
        return cls.population

# インスタンス化
person1 = Person("Alice")
person2 = Person("Bob")

# クラスメソッドの呼び出し
print(Person.get_population())  # 2

class Car:
    def __init__(self, make, model, year):
        self.make = make
        self.model = model
        self.year = year
        self.odometer_reading = 0

    def describe_car(self):
        return f"{self.year} {self.make} {self.model}"

    def read_odometer(self):
        return f"This car has {self.odometer_reading} miles on it."

    def update_odometer(self, mileage):
        if mileage >= self.odometer_reading:
            self.odometer_reading = mileage
        else:
            print("You can't roll back an odometer!")

    def increment_odometer(self, miles):
        self.odometer_reading += miles

my_car = Car("Toyota", "Corolla", 2020)
print(my_car.describe_car())  # "2020 Toyota Corolla"
my_car.update_odometer(15000)
print(my_car.read_odometer())  # "This car has 15000 miles on it."
my_car.increment_odometer(100)
print(my_car.read_odometer())  # "This car has 15100 miles on it."

class ElectricCar(Car):
    def __init__(self, make, model, year, battery_size=75):
        super().__init__(make, model, year)
        self.battery_size = battery_size

    def describe_battery(self):
        return f"This car has a {self.battery_size}-kWh battery."

my_electric_car = ElectricCar("Tesla", "Model 3", 2021)
print(my_electric_car.describe_car())  # "2021 Tesla Model 3"
print(my_electric_car.describe_battery())  # "This car has a 75-kWh battery."