単一継承

導入

子クラスの定義

class Animal:
    def __init__(self, name): self.name = name
    def speak(self): return '...'
class Dog(Animal):
    def speak(self): return 'Woof'
d = Dog('Rex')
print(d.name, d.speak())

super().__init__の呼び出し

class Animal:
    def __init__(self, name): self.name = name
class Dog(Animal):
    def __init__(self, name, breed):
        super().__init__(name)
        self.breed = breed
d = Dog('Rex', 'Labrador')
print(d.name, d.breed)

メソッドの継承

class Vehicle:
    def start(self): return 'starting'
class Car(Vehicle):
    pass
print(Car().start())

メソッドのオーバーライド

class Shape:
    def area(self): return 0
class Square(Shape):
    def __init__(self, s): self.s = s
    def area(self): return self.s**2
print(Square(4).area())

親クラスの動作の拡張

class Animal:
    def describe(self): return 'I am an animal'
class Dog(Animal):
    def describe(self): return super().describe() + ' and a dog'
print(Dog().describe())

isinstance()とissubclass()

class Animal: pass
class Dog(Animal): pass
d = Dog()
print(isinstance(d, Animal))
print(issubclass(Dog, Animal))

子クラスによる新しいメソッドの追加

class Animal:
    def __init__(self, name): self.name = name
class Dog(Animal):
    def fetch(self): return f'{self.name} fetches!'
print(Dog('Rex').fetch())

保護された属性

class Animal:
    def __init__(self, name): self._name = name
    def name(self): return self._name
class Dog(Animal):
    def bark(self): return f'{self._name} barks'
print(Dog('Rex').bark())

抽象基底クラス

from abc import ABC, abstractmethod
class Shape(ABC):
    @abstractmethod
    def area(self): pass
class Circle(Shape):
    def __init__(self, r): self.r = r
    def area(self):
        import math
        return math.pi * self.r**2
print(Circle(3).area())

__bases__と__mro__

class A: pass
class B(A): pass
class C(B): pass
print(C.__mro__)

確認問題

復習

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