继承

继承介绍

'''
1.什么是继承?
    在程序中继承是一种新建子类的方式,新创建的类称之为子类\派生类,被继承的类称之为父类\基类\超类
    继承描述的是一种遗传关系,子类可以重用父类的属性

2.为何用继承?
    减少类与类之间代码冗余的问题

3.如何继承?
    先抽象再继承
'''
#在python中继承的特点? 单继承&多继承
class Parent1(object):
    pass

class Parent2:
    pass

class Sub1(Parent1):
    pass

class Sub2(Parent1,Parent2):
    pass

print(Sub1.__bases__)
print(Sub2.__bases__)

print(Parent1.__bases__)
print(Parent2.__bases__)

x=2
class Foo:
    x=1
    pass
obj=Foo()
# obj.x=3
print(obj.x)


'''
python2与python3在继承上的区别
新式类:但凡继承object类的子类,以及该子类的子子类,......都称之为新式类
经典类:没有继承object类的子类,以及该子类的子子类,......都称之为经典类
只有在python2中才区分新式类和经典类
新式类与经典类在属性查找上的区别?
'''

基于继承的代码冗余问题

# 在子类派生出的新功能中如何重用父类的功能:
# 方式一:指明道姓地访问某一个类中的函数,与继承无关
class OldboyPeople:
    school = 'Oldboy'
    def __init__(self,name,age,gender):
        self.name = name
        self.age = age
        self.gender = gender

# print(OldboyPeople.__init__)

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

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

class OldboyTeacher(OldboyPeople):
#         tea,'egon',18,'male',10,3000
    def __init__(self,name,age,gender,level,salary):
        self.name = name
        self.age = age
        self.gender = gender
        OldboyPeople.__init__(self,name,age,gender)

        self.level=level
        self.salary=salary

    def score(self,stu,num):
        stu.num=num
        print('老师%s给学生%s打分%s'%(self,name,stu.name,num))

stu=OldboyStudent('kevin',38,'male')  # __init__(stu1,'kevin',38,'male'10,3000)
print(stu.__dict__)
tea=OldboyTeacher('egon',18,'male',10,3000) #  __init__(stu1,'kevin',38,'male'10,3000)
print(tea.__dict__)

print(stu.school)
print(tea.school)

在单继承背景下的属性查找

# 在单继承背景下,无论是新式类还是经典类属性查找顺序都一样
# 先obj->类->父类->...
class Foo:
    def f1(self):
        print('Foo.f1')

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

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

obj=Bar()
obj.f2()
# 在多继承背景下,如果一个子类继承了多个分支,但是多个分支没有汇聚到一个非object类,无论是新式类还是经典类属性查找顺序都一样:
# 会按照从左到右的顺序一个分支一个分支的查找下去

class E:
    # xxx='E'
    pass

class F:
    # xxx='F'
    pass

class B(E):
    # xxx='B'
    pass

class C(F):
    # xxx='C'
    pass

class D:
    # xxx='D'
    pass

class A(B,C,D):
    # xxx='A'
    pass

obj=A()
# obj.xxx=111
# print(obj.xxx)
print(A.mro())

# 在多继承背景下,如果一个字类继承了多个分支,但是多个分支,最终汇聚到一个非object类(菱形继承问题)
# 新式类:广度优先查找:obj->A->B->E->C->F->D->G->object
# 经典类:深度优先查找:obj->A->B->E->G->C->F->D
class G:
    xxx = 'G'
    
class E(G):
    xxx = 'E'
    pass

class F(G):
    xxx = 'F'
    pass

class C(F):
    xxx = 'C'
    pass

class D(G):
    xxx = 'D'
    pass

class A(B,C,D):
    xxx = 'A'
    pass

print(A.mro())

super方法

# 在子类派生出的新功能中如何重用父类的功能:
# 方式一:指明道姓地访问某一个类中的函数,与继承无关
# 方式二:super(OldboyTeacher,self),在python3中super可以不传参数,调用该函数会得到一个特殊的对象,该对象专门用来访问父类中属性
#        强调:super会严格参照类的mro列表依次查找属性
class OldboyPeple:
    school = 'Oldboy'
    def __init__(self,name,age,gender):
        self.name = name
        self.age = age
        self.gender = gender

class OldboyTeacher(OldboyPeple):
            #   tea,'egon',18,'male',10,3000
    def __init__(self,name,age,gender,level,salary):
        OldboyPeple.__init__(self,name,age,gender)
        super(OldboyTeacher,self).__init__(name,age,gender)

        self.level = level
        self.salary = salary

    def score(self,stu,num):
        stu.num = num
        print('老师%s给学生%s打分%s'%(self.name,stu.name,num))

tea=OldboyTeacher('egon',18,'male',10,3000) #__init__(tea,'egon',18,'male',10,3000)
print(tea.__dict__)
# print(stu.school)