类的继承和多态

Posted 2020-10-30 Ryansuperwa

继承

1、什么是继承？

继承是一种新建类的方式

新建的类称之为类或者派生类，

父类又可以称之为基类或者超类

子类会‘遗传’父类的属性

继承是类与类之间的关系，寻找这种关系需要先抽象再继承

2、为什么要用继承

减少代码冗余

3、怎么用继承

class parentclass1：
    pass
class parentclass2:
    pass
class subclass1(parentclass1):
    pass
class subclass2(parentclass1,parentclass2):#这就是继承上面
    pass


print（subclass2.__bases__）#这个bases就是查看有几个‘爹’的

那我们能从“爹”那里能继承什么呢？

class parent1:
    school=‘oldboy’
    def __init__(self, name,age,sex):
        self.name=name
        self.age=age
        self.sex=sex
class parent2:
　　school=\'oldboy\'
　　def __init__(self,name,age,sex):
　　　　self.name=name
　　　　self.age=age
　　　　self.sex=sex


class son1(parent1):
    def f1(self):
        print(\'%s son1\'%self.name)
class son2(parent1,parent2):
    def f2(self):
        print(\'%s son2\'%self.name)

猜一猜  f2中的f1，调用的到底是哪里的？是自己的还是儿子的

调用的是儿子辈的。不是根据就近原则找自己的而是找儿子的

class foo():          #爹
    def f1(self):
        print(\'fool.f1\')
    def f2(self):
        print(\'foo.f2\')
        self.f1()

class bar(foo):    #儿子
    def f1(self):
        print(\'bar.f1\')    

派生：子类定义自己新的属性，如果与父辈同名，以子类自己为准

class OldboyPeople:
#     school = \'oldboy\'
#
#     def __init__(self, name, age, sex):
#         self.name = name
#         self.age = age
#         self.sex = sex
#
#     def f1(self):
#         print(\'爹的f1\')
 class OldboyTeacher(OldboyPeople):
#     def change_score(self):
#         print(\'teacher %s is changing score\' %self.name)
#
#     def f1(self):
#         print(\'儿子的f1\')
#
# tea1 = OldboyTeacher(\'egon\', 18, \'male\')
# tea1.f1(class OldboyPeople:

    school = \'oldboy\'
class OldboyPeople:
    def __init__(self, name, age, sex):
        self.name = name
        self.age = age
        self.sex = sex

    def f1(self):
        print(\'爹的f1\')

class OldboyTeacher(OldboyPeople):
    def __init__(self,name,age,sex,level,salary):#应用自己的，不用父辈了

        self.name=name
        self.age=age
        self.sex=sex

        self.level=level
        self.salary=salary

    def change_score(self):
        print(\'teacher %s is changing score\' %self.name)

    def f1(self):
        print(\'儿子的f1\')

tea1 = OldboyTeacher(\'egon\', 18, \'male\',9,3.1)
print(tea1.name,tea1.age,tea1.sex,tea1.level,tea1.salary)

 子类派生出的新方法中重用父辈的功能：

方法一：指名道姓地调用（其实与继承没有什么关系的）

OldboyPeople.__init__(self,name, age, sex)

# class OldboyPeople:
#     school = \'oldboy\'
#
#     def __init__(self, name, age, sex):
#         self.name = name
#         self.age = age
#         self.sex = sex
#
#     def tell_info(self):
#         print("""
#         ===========个人信息==========
#         姓名：%s
#         年龄：%s
#         性别：%s
#         """ %(self.name,self.age,self.sex))
#
#
# class OldboyTeacher(OldboyPeople):
#     #            tea1,\'egon\', 18, \'male\', 9, 3.1
#     def __init__(self, name, age, sex, level, salary):
#         # self.name = name
#         # self.age = age
#         # self.sex = sex
#         OldboyPeople.__init__(self,name, age, sex)#指名道姓的应用
#
#         self.level = level
#         self.salary = salary
#
#     def tell_info(self):
#         OldboyPeople.tell_info(self)
#         print("""
#         等级：%s
#         薪资：%s
#         """ %(self.level,self.salary))
#
# tea1 = OldboyTeacher(\'egon\', 18, \'male\', 9, 3.1)
# # print(tea1.name, tea1.age, tea1.sex, tea1.level, tea1.salary)
#
#
# tea1.tell_info()

方法二：super()调用（严格依赖于继承）

super()的返回值是一个特殊的对象，该对象专门用来调用父类中的属性

#了解再python2中，需要super（自己的类名，self）

class OldboyPeople:
    school = \'oldboy\'

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

    def tell_info(self):
        print("""
        ===========个人信息==========
        姓名：%s
        年龄：%s
        性别：%s
        """ %(self.name,self.age,self.sex))


class OldboyTeacher(OldboyPeople):
    #            tea1,\'egon\', 18, \'male\', 9, 3.1
    def __init__(self, name, age, sex, level, salary):
        # OldboyPeople.__init__(self,name, age, sex)
        super(OldboyTeacher,self).__init__(name,age,sex)

        self.level = level
        self.salary = salary

    def tell_info(self):
        # OldboyPeople.tell_info(self)
        super().tell_info()
        print("""
        等级：%s
        薪资：%s
        """ %(self.level,self.salary))

tea1 = OldboyTeacher(\'egon\', 18, \'male\', 9, 3.1)
# print(tea1.name, tea1.age, tea1.sex, tea1.level, tea1.salary)
tea1.tell_info()

二、经典类与新式类

1、新式类：

　　继承object的类，以及该类的子类，都是新式类，在python3中，如果一个类没有指定继承父辈，默认就继承object

所以说python3中所有的类都是新式类

 

2、经典类：

　　没有继承object的类，以及该类的子类，都是经典类

 

 

三、在棱形继承背景下，super严格按照查找属性

1、经典类：深度优先

先f--》d--》b--》a 找到了就不找了。一条道路走到黑

 

2、新式类：广度优先

先f--》d--》b--》e--》c--》a 按照菱形找

 

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

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()

# F->D->B->E->C-A->object

print(F.mro())