多重继承

Python 面向对象编程进阶

Jake Roach

Data Engineer

多重继承

允许一个类继承多个类的功能

Intern 可同时继承 Employee 与 Student
保持"是一个（is-a）"关系

Intern 类同时继承 Employee 与 Student 类。

class Employee:
  def __init__(self, department):
    self.department = department

  def begin_job(self):
    print(f"Welcome to {self.department}!")

class Student:
  def __init__(self, school):
    self.school = school
    self.courses = []

  def add_course(self, course_name):
    self.courses.append(course_name)

多重继承

class Intern(Employee, Student):
    def __init__(self, department, school, duration):
        # 同时调用两个构造函数
        Employee.__init__(self, department)
        Student.__init__(self, school)
        self.duration = duration

    def onboard(self, mentor):
        # 新方法的实现
        ...

创建 Intern 对象

stephen = Intern("Software Development", "Echo University", 10)
stephen.begin_job()  # Method from Employee

Welcome to Software Development!

stephen.add_course("Intermediate OOP in Python")  # Method from Intern
print(stephen.courses)

["Intermediate OOP in Python"]

多级继承

继承一个已继承自另一类的类，成为"孙类"

维持"是一个（is-a）"关系

多级继承示意图。

class Person:
  def __init__(self, name):
    self.name = name

  def introduce(self):
      print(f"Hello, my name is {self.name}")

class Employee(Person):
  def __init__(self, name, title):
    Person.__init__(self, name)
    self.title = title

  def change_position(self, new_title):
    print(f"Starting new role as {new_title}")
    self.title = new_title

多级继承

class Manager(Employee):
  def __init__(self, name, title, number_reports):
    Employee.__init__(self, name, title)
    self.number_reports = number_reports

mike = Manager("Mike", "Engineering Manager", 14)
mike.introduce()
mike.change_position("Director of Engineering")
print(mike.number_reports)

Hello, my name is Mike
Starting new role as Director of Engineering
14

方法解析顺序（MRO）

当父类与子类实现同名方法时，Python 决定调用哪个方法的顺序

确定 MRO 的规则：

先从子类开始查找
按类定义中的从左到右顺序查找父类

.mro() 方法与 __mro__

子类继承多个父类。

¹ Beyond the Basic Stuff with Python, Sweigart（第311页）

方法解析顺序（MRO）

class Intern(Employee, Student):  # Intern inherits the Employee and the Student classes
  ...

# Find the MRO for Intern
print(Intern.mro())

[<class '__main__.Intern'>, <class '__main__.Employee'>, <class '__main__.Student'>, <class 'object'>]

# Find the MRO using __mro__
print(Intern.__mro__)

(<class '__main__.Intern'>, <class '__main__.Employee'>, <class '__main__.Student'>, <class 'object'>)

让我们来练习！

Python 面向对象编程进阶