2020-09-24

Python 多重繼承 multiple inheritance

本篇介紹 Python 多重繼承 multiple inheritance 的寫法，

Python 多重繼承(Multiple Inheritance)的寫法

Python multiple inheritance 最簡單的多重繼承寫法如下，
有 BaseClass1, BaseClass2, DerivedClass 三個類別
DerivedClass 多重繼承 BaseClass1 和 BaseClass2

python-multiple-inheritance.py

#!/usr/bin/env python3
# -*- coding: utf-8 -*-

class BaseClass1:
    pass

class BaseClass2:
    pass

class DerivedClass(BaseClass1, BaseClass2):
    pass

derived = DerivedClass()

方法覆寫(Method Overriding)

Dog3 多重繼承了 Dog1 和 Dog2，如果沒有覆寫父類的 eat，呼叫子類 Dog3.eat() 時會繼承的前面/左邊父類(Dog1)方法優先，

python-multiple-inheritance2.py

#!/usr/bin/env python3
# -*- coding: utf-8 -*-

class Dog1:
    def eat(self):
        print("Dog1 class eat method is called.")

class Dog2:
    def eat(self):
        print("Dog2 class eat method is called.")

class Dog3(Dog1, Dog2):
    pass

dog = Dog3()
dog.eat()

結果輸出如下，

1	Dog1 class eat method is called.

子類建構子(Constructor)傳遞參數到父類建構子

在多重繼承的情況下，子類建構子又是如何傳遞參數到父類的建構子，這邊來介紹一下，
呼叫

python-multiple-inheritance3.py

#!/usr/bin/env python3
# -*- coding: utf-8 -*-

class Dog1:
    def __init__(self, name):
        print("Dog1 ", name)

    def eat(self):
        print("Dog1 class eat method is called.")

class Dog2:
    def __init__(self, sex):
        print("Dog2 ", sex)

    def eat(self):
        print("Dog2 class eat method is called.")

class Dog3(Dog2):
    def __init__(self, sex):
        print("Dog3 ", sex)
        Dog2.__init__(self, sex)

    def eat(self):
        print("Dog3 class eat method is called.")

class Dog4(Dog1, Dog3):
    def __init__(self, name, sex):
        Dog1.__init__(self, name)
        Dog3.__init__(self, sex)

#dog = Dog4(name="Harry", sex="female")
dog = Dog4("Harry", "female")
dog.eat()

結果輸出如下，

Dog1  Harry
Dog3  female
Dog2  female
Dog1 class eat method is called.

參考
Classes — Python 3.9.0 documentation
https://docs.python.org/3/tutorial/classes.html#multiple-inheritance
Python 速查手冊 - 6.9 多重繼承
http://kaiching.org/pydoing/py/python-multiple-inheritance.html
程式語言教學誌 FB, YouTube: PYDOING: Python 3.1 快速導覽 - 類別多重繼承
https://pydoing.blogspot.com/2011/01/python-multiple.html
Python-QA/Python多重繼承屬性問題.md at master · dokelung/Python-QA
https://github.com/dokelung/Python-QA/blob/master/questions/object/Python%E5%A4%9A%E9%87%8D%E7%B9%BC%E6%89%BF%E5%B1%AC%E6%80%A7%E5%95%8F%E9%A1%8C.md