Python继承的作用和菱形问题

Myth丶恋晨 2022-10-09 00:36 114阅读 0赞

**继承的作用**

可以利用继承来减少代码冗余

class Person:
        school='aaaa'
    
        def __init__(self,name,age,):
            self.name=name
            self.age=age

![519367a30983d9035b1498463f97545a.png][]

class Teacher(Person):
        pass
    
    class Student(Person):
        pass
    
    #类实例化会自动调用__init__如果类中没有,去父类中找
    # stu1=Student() #报错,因为父类中必须传两个参数
    stu1=Student('nick',18)
    print(stu1.school)

**多层继承**

''' Python大型免费公开课，适合初学者入门 加QQ群：579817333 获取学习资料及必备软件。 '''
    class A:
        a="AAAA"
    class B(A):
        a="BBB"
    
    class C(B):
        # a="CCC"
        pass
    
    
    class D(C):
        # a = "DDD"
        pass
    
    d=D()
    print(d.a)

**多继承**

class A:
        # a="AAAA"
        pass
    class B:
        # a="BBB"
        pass
    
    class C:
        a="CCC"
        pass
    
    class D(A,B,C):
        # a = "DDD"
        pass
    
    d=D()
    print(d.a)

**继承的菱形问题**

新式类和经典类的查找顺序是不一样的

新式类的查找属性:广度优先

经典类:深度优先

# class G(object):
    # a = "GGG"
    # pass
    # class F(G):
    # # a = "FFF"
    # pass
    # class E(G):
    # # a = "EEE"
    # pass
    # class D(G):
    # # a = "DDD"
    # pass
    # class C(F):
    # # a="CCC"
    # pass
    # class B(E):
    # # a="BBB"
    # pass
    # class A(B,C,D):
    # # a="AAAA"
    # pass
    #
    # a=A()
    # print(a.a)
    
    class G(object):
        a = "GGG"
        pass
    class F(G):
        # a = "FFF"
        pass
    class E(G):
        # a = "EEE"
        pass
    class D(G):
        # a = "DDD"
        pass
    class C(F):
        # a="CCC"
        pass
    class B(E):
        # a="BBB"
        pass
    class A(B,C,D):
        # a="AAAA"
        pass
    a=A()
    print(a.a)
    #mro 列表,继承顺序查找列表(只在新式类中有)1
    print(A.mro())
    print(A.__mro__)

GGG

[<class 'main.A'>, <class 'main.B'>, <class 'main.E'>, <class 'main.C'>, <class 'main.F'>, <class 'main.D'>, <class 'main.G'>, <class 'object'>]
    (<class 'main.A'>, <class 'main.B'>, <class 'main.E'>, <class 'main.C'>, <class 'main.F'>, <class 'main.D'>, <class 'main.G'>, <class 'object'>)

继承的菱形问题(显示的都继承一个类，不是object类)：新式类和经典类的查找顺序是不一样的

*  新式类（py3中全是新式类）：广度优先—从左侧开始，一直往上找，找到菱形的顶点结束（不包括菱形顶点），继续下一个继承的父类往上找，找到菱形的顶点结束（不包括菱形顶点），最后找到菱形顶点
 *  经典类（只有py2中才有）：深度优先—从左侧开始，一直往上找，找到菱形的顶点结束（包括菱形顶点）继续下一个继承的父类往上找，找到菱形的顶点结束(不包含菱形定点)

不出现菱形问题:正常查找

[519367a30983d9035b1498463f97545a.png]: /images/20221005/f23237e035df4b4082995932f2b4f2ff.png