内容概要

• 面向对象的三大特征
  1.封装
  2.继承
  3.多态
• 继承的属性查找顺序
  1.单继承下的属性查找
  2.多继承下的属性查找
• super()和mro列表
• 多态与多态性

继承

1.什么是继承
继承就是新建类的一种方式，新建的类我们成为子类或派生类，被继承的类我们成为父类或基类
子类可以使用父类中的属性或方法

2.为什么要用继承
类解决了对象与对象之间的代码冗余问题
继承解决了类与类之间的代码冗余问题

3.如何使用继承
新式类：继承了object类的子子孙孙类都是新式类
经典类：没有继承object类的子子孙孙类都是经典类

新式类和经典类只有在python2中有区分

类的继承

# 父类
class People():
    school = 'zj'

    def __init__(self, name, age, hobby):
        self.name = name
        self.age = age
        self.hobby = hobby


# 学生类(子类)
class Student(People):

    def __init__(self, name, age, hobby, course=None):
        if course is None:
            course = []
        People.__init__(self, name, age, hobby)
        self.courses = course

    def choice_course(self, course):
        self.courses.append(course)
        print('学生%s选择%s课程' % (self.name, self.courses))


stu = Student('aaa', 18, 'music')
stu.choice_course('music')


# 教师类(子类)
class Teacher(People):

    def __init__(self, name, age, hobby, ):
        People.__init__(self, name, age, hobby)

    def score(self, stu1, stu2, score):
        print('教师%s给%s的%s课程打%s分' % (self.name, stu1, stu2, score))


tea = Teacher('sss', 27, 'run')
tea.score('aaa', 'music', 90)

单继承下属性查找

class Animal():
    def dog(self):
        print('is dog')

    def cat(self):
        print('is cat')
        self.dog()


class Crawl(Animal):
    def dog(self):
        print('one dog')


obj = Crawl()
obj.cat()

练习

class Animal():
    def __dog(self):  # _Animal__dog
        print('is dog')

    def cat(self):
        print('is cat')
        self.__dog()  # _Animal__dog


class Crawl(Animal):
    def __dog(self):  # _Crawl__dog
        print('one dog')


obj = Crawl()
obj.cat()

多继承下的属性查找

新式类：按照广度优先查询
经典类：按照深度优先查询

class A():
    def test(self):
        print('from A')


class B(A):
    def test(self):
        print('from B')


class C(A):
    def test(self):
        print('from C')


class D(B):
    def test(self):
        print('from D')


class E(C):
    def test(self):
        print('from E')


class F(D, E):
    def test(self):
        print('from F')


obj = F()
obj.test()

super()和mro()列表

super()用法

# 父类
class People():
    school = 'zj'

    def __init__(self, name, age, hobby):
        self.name = name
        self.age = age
        self.hobby = hobby


# 学生类(子类)
class Student(People):

    def __init__(self, name, age, hobby, course=None):
        if course is None:
            course = []
        # People.__init__(self, name, age, hobby)
        # super(Student, self)返回一个特殊对象
        # 他的使用遵循mro列表
        super(Student, self).__init__(name, age, hobby)
        self.courses = course

    def choice_course(self, course):
        self.courses.append(course)
        print('学生%s选择%s课程' % (self.name, self.courses))


stu = Student('aaa', 18, 'music')
print(stu.name)


# 教师类(子类)
class Teacher(People):

    def __init__(self, name, age, hobby, ):
        # People.__init__(self, name, age, hobby)
        super().__init__(name, age, hobby)

    def score(self, stu1, stu2, score):
        print('教师%s给%s的%s课程打%s分' % (self.name, stu1, stu2, score))


tea = Teacher('sss', 27, 'run')
print(tea.age)

mro列表
练习1

class A:
    def test(self):
        print('from A.test')
        super().test()


class B:
    def test(self):
        print('from B')


class C(A, B):
    pass


c = C()
c.test()
print(C.__mro__)

练习2

class A:
    def test(self):
        print('A---->test')
        super().aaa()


class B:
    def test(self):
        print('B---->test')

    def aaa(self):
        print('B---->aaa')


class C(A, B):
    def aaa(self):
        print('C----->aaa')


c = C()
c.test()
print(C.__mro__)

练习3

class A:
    def test(self):
        print('A---->test')
        super().aaa()


class B:
    def test(self):
        print('B---->test')

    def aaa(self):
        print('B---->aaa')


class C(A, B):
    def aaa(self):
        print('C----->aaa')


c = A()
print(A.__mro__)
c.test()  # 报错

多态与多态性

什么事多态
水：液态水，固态水，气态水

import abc


# 抽象类： 抽象类只能被继承，不能被实例化
class Animal(metaclass=abc.ABCMeta):

    @abc.abstractmethod  # 该方法已经是抽象方法了
    def speak(self): pass

    @abc.abstractmethod
    def login(self): pass


class People(Animal):
    def speak(self):
        # print('嗷嗷嗷')
        pass

    def login(self):
        pass


class Pig(Animal):
    def speak(self):
        print('哼哼哼')


class Dog(Animal):
    def speak(self):
        print('汪汪汪')


obj = People()
obj.speak()

# 多态练习
class Pig():
    def speak(self):
        print('哼哼哼')


class Dog():
    def speak(self):
        print('汪汪汪')

class Txt():
    def speak(self):
        print('Txt')

obj = People()
obj1 = Pig()
obj2 = Dog()
obj3 = Txt()

# 多态带来的特性：在不用考虑对象数据类型的情况下，直接调用对应的函数

def animal(animal):
    return animal.speak()

animal(obj)
animal(obj1)
animal(obj2)
animal(obj3)

# 父类限制子类的行为
class Animal():
    def speak(self):
        raise Exception("必须实现speak方法")

标签：__,多态性,self,面向对象,test,三大,print,class,def
来源： https://www.cnblogs.com/sly0/p/15649917.html