python面向对象之继承

python面向对象之继承

  ·  继承

  ·  类的继承

  ·  单继承下属性查找

  ·  多继承下属性的查找

  ·  super()和mro列表

  ·  多态与多态性

  一、继承

    1.什么是继承？

        继承就是新建类的一种方式，新建的类我们称为子类或者叫派生类，被继承的类我们称为父类或基类

        子类可以使用父类中的属性或者方法

    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

        继承解决的是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类的子子孙孙都是新式类

        经典类：没有继承了object类的子子孙孙都是经典类

        新式类与经典类只有在python2中区分

  二、类的继承

# 以学生选课系统为例
# 父类，公共类
class People():
    school = 'SH'

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

# 学生类
class Student(People):

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

    def choose_course(self, course):
        self.courses.append(course)
        print('%s 选课成功 %s' % (self.name, self.courses))


stu = Student('ly', 19, 'male')

# teacher类
class Teacher(People):

    def __init__(self, name, age, gender, level):
        self.level = level
        People.__init__(self, name, age, gender)

    def score(self, stu_obj, score):
        stu_obj.score = score  # 给学生打分
        print('%s给%s打了%s分' % (self.name, stu_obj.name, score))


tea = Teacher('ly', 19, 'male', 10)
print(tea.name)
print(tea.level)

    三、单继承下属性查找

class Foo:
    def f1(self):
        print('Foo.f1')

    def f2(self):
        #
        print('Foo.f2')
        self.f1()


class Bar(Foo):
    def f1(self):
        print('Bar.f1')


obj = Bar()  # {}
obj.f2()


# 练习
class Foo:
    def __f1(self):  # _Foo__f1()
        print('Foo.f1')

    def f2(self):
        #
        print('Foo.f2')
        self.__f1()  # _Foo__f1()


class Bar(Foo):
    def __f1(self):  # # _Bar__f1()
        print('Bar.f1')


obj = Bar()  # {}
obj.f2()

    四、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(object):
    def test(self):
        print('from A')


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

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


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

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


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


f1 = F()
f1.test()

    五、super()和mro列表

class People():
    school = 'SH'

    def __init__(self, name, age, gender):
        self.name = name
        self.age = age
        self.gender = gender
        
class Teacher(People):

    def __init__(self, name, age, gender, level):
        self.level = level
        super().__init__(name, age, gender) # super的使用

        
# 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()


# mro列表练习2 
class B:
    def test(self):
        print('B---->test')

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

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


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


c = A()
# c.test()  # 打印结果:
print(A.mro())

    六、多态与多态性

        1.什么是多态

        水：液态水，固态水，气态水

        动物：人、猪、狗、猫

# 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")