面向对象继承与派生

1、什么是继承?

继承是一种新建类的方式，新建的类称为子类，被继承的类称为父类

继承的特性是：子类会遗传父类的属性

强调：继承是类与类之间的关系

2、为什么要用继承

继承的好处就是可以减少代码的冗余

3、如何用继承

在python中支持一个类同时继承多个父类

        在python3中如果一个类没有继承任何类，那默认继承object；

        在python2中如果一个类没有继承任何类，不会继承object类

新兴类

       但凡继承了object的类以及该类的子类，都是新式类；

       没有继承object的类以及该类的子类，都是经典类

（在python3中都是新式类，只有在python中才区别新式类与经典类）

class Parent1(object):
    pass

class Parent2(object):
    pass
class Sub1(Parent1,Parent2):
    pass
print(Sub1.__bases__)  #(<class '__main__.Parent1'>, <class '__main__.Parent2'>)
print(Parent1.__bases__) #(<class 'object'>,)
print(Parent2.__bases__) #(<class 'object'>,)

继承应用

# class OldboyPeople:
#     school = 'oldboy'
#
# class OldboyStudent:
#     school='oldboy'
#     def __init__(self,name,age,sex):
#         self.name=name
#         self .age= age
#         self .sex=sex
#     def choose_course(self):
#         print('%s is choosing course'%(self.name))
#
#
# class OldboyTeacher:
#     school= 'Oldboy'
#     def __init__(self,name,age,sex,level):
#         self.name= name
#         self .age= age
#         self.sex= sex
#         self .level= level
#
#     def score(self):
#         print('%s is scoring'%self .name)
#
# stu1= OldboyStudent('haoge',34,'male')
# tea1=OldboyTeacher('egon',44,'gg',20)
#
# stu1.choose_course()
# tea1.score()
#
# print(stu1.school) #查找属性的顺序：对象自己》对象的类》父类。。

4、派生

（1）#派生：子类中新定义的属性，子类在使用时始终以自己的为准
class OldboyPeople:
    school = 'oldboy'     #子类中相同的属性
    def __init__(self,name,age,sex):
        self.name=name
        self .age= age
        self .sex=sex
class OldboyStudent(OldboyPeople):
    school='oldboy'

    def choose_course(self):
        print('%s is choosing course'%(self.name))


class OldboyTeacher(OldboyPeople):
    school= 'Oldboy'
    def __init__(self,name,age,sex,level):
        OldboyPeople.__init__(self ,name,age,sex) #调用父集的属性
        self .level= level

    def score(self,stu_obj,num):
        print('%s is scoring'%self .name)


stu1 = OldboyStudent('haoge', 34, 'male')
tea1=OldboyTeacher('egon',44,'gg',20)

tea1.score(stu1,99)

（2）在子类派生的新方法中重用父类功能的两种方式

# 方式一：与继承无关
#指名道姓法，直接用：类名.函数名
# class OldboyPeople:
#     school = 'oldboy'
#
#     def __init__(self, name, age, sex):
#         self.name = name
#         self.age = age
#         self.sex = sex
#
# class OldboyStudent(OldboyPeople):
#     def __init__(self,name,age,sex,stu_id):
#         OldboyPeople.__init__(self,name,age,sex)
#         self.stu_id=stu_id
#
#     def choose_course(self):
#         print('%s is choosing course' %self.name)
#
# stu1= OldboyStudent('猪哥',66,'mal',10)
# stu1.choose_course()
# print(stu1 .school)
# print(stu1 .name )


# 方式二：严格以继承属性查找关系
# super()会得到一个特殊的对象，该对象就是专门用来访问父类中的属性的（按照继承的关系）
# super().__init__(不用为self传值)
# 注意：
# super的完整用法是super(自己的类名,self),在python2中需要写完整，而python3中可以简写为super()
class OldboyPeople:
    school = 'oldboy'

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

class OldboyStudent(OldboyPeople):
    def __init__(self,name,age,sex,stu_id):
        super().__init__(name,age,sex)   #完整写法super( OldboyStudent,self).__init__(name,age,sex))
        self.stu_id=stu_id

    def choose_course(self):
        print('%s is choosing course' %self.name)


stu1=OldboyStudent('猪哥',19,'male',1)
print(stu1.__dict__)

print(OldboyStudent.mro()) #根据c3算法获取继承顺序进行查找

例题：

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

class B:
    def f2(self):
        super().f1()      #重用父类功能A.f1(self)
        print('B.f2')

class C(B,A):
    pass

obj=C()
print(C.mro()) #   查找顺序C-》B->A->object
obj.f2()