內容概要

• 面向物件的三大特徵
  1.封裝
  2.繼承
  3.多型
• 繼承的屬性查詢順序
  1.單繼承下的屬性查詢
  2.多繼承下的屬性查詢
• super()和mro列表
• 多型與多型性

繼承

1.什麼是繼承
繼承就是新建類的一種方式，新建的類我們成為子類或派生類，被繼承的類我們成為父類或基類
子類可以使用父類中的屬性或方法

2.為什麼要用繼承
類解決了物件與物件之間的程式碼冗餘問題
繼承解決了類與類之間的程式碼冗餘問題

3.如何使用繼承
新式類：繼承了object類的子子孫孫類都是新式類
經典類：沒有繼承object類的子子孫孫類都是經典類

新式類和經典類只有在python2中有區分

類的繼承

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

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


# 學生類(子類)
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('學生%s選擇%s課程' % (self.name, self.courses))


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


# 教師類(子類)
class Teacher(People):

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

    def score(self, stu1, stu2, score):
        print('教師%s給%s的%s課程打%s分' % (self.name, stu1, stu2, score))


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

單繼承下屬性查詢

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()

練習

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()
 

多繼承下的屬性查詢

新式類：按照廣度優先查詢
經典類：按照深度優先查詢

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

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

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


# 學生類(子類)
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)返回一個特殊物件
        # 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('學生%s選擇%s課程' % (self.name, self.courses))


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


# 教師類(子類)
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('教師%s給%s的%s課程打%s分' % (self.name, stu1, stu2, score))


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

mro列表
練習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__)

練習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__)

練習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()  # 報錯

多型與多型性

什麼事多型
水：液態水，固態水，氣態水

import abc


# 抽象類： 抽象類只能被繼承，不能被例項化
class Animal(metaclass=abc.ABCMeta):

    @abc.abstractmethod  # 該方法已經是抽象方法了
    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()

# 多型練習
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()

# 多型帶來的特性：在不用考慮物件資料型別的情況下，直接呼叫對應的函式

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

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

# 父類限制子類的行為
class Animal():
    def speak(self):
        raise Exception("必須實現speak方法")