20、继承的应用、super、组合
Day 20
一、继承应用+super的基本用法
class People:
school = '虹桥校区'
def __init__(self, name, age, gender):
self.name = name
self.age = age
self.gender = gender
class Student(People):
def choose(self):
print('%s 选课成功' % self.name)
class Teacher(People):
def __init__(self, name, age, gender, level):
# 方式一: 指名道姓地引用某一个类的函数，与继承无关
# People.__init__(self, name, age, gender)
# 方式二: super()返回一个特殊的对象，该对象会参考发起
属性查找的那一个类的mro列表，去当前类的父类中找属性，严
格依赖继承
super(Teacher, self).__init__(name, age, gender)
self.level = level
def score(self):
print('%s正在为学生打分' % self.name)
stu1 = Student('jack', 18, 'male')
stu2 = Student('tom', 38, 'male')
stu3 = Student('lili', 28, 'female')
tea1 = Teacher('egon', 18, 'male', 10)
tea2 = Teacher('lxx', 38, 'male', 3)
print(stu1.__dict__)
print(stu2.__dict__)
print(stu3.__dict__)
print(tea1.__dict__)
print(tea2.__dict__)
======================输出结果=========================
{'name': 'jack', 'age': 18, 'gender': 'male'}
{'name': 'tom', 'age': 38, 'gender': 'male'}
{'name': 'lili', 'age': 28, 'gender': 'female'}
{'name': 'egon', 'age': 18, 'gender': 'male', 'level': 10}
{'name': 'lxx', 'age': 38, 'gender': 'male', 'level': 3}
面向对象代码，写着烦，用着爽！！！
二、继承实现原理
python会根据C3算法给你算出mro列表出来
如果是单继承，一层一层的向上找。
class C:
x = 333
class B(C):
x = 222
class A(B):
# x = 111
pass
print(B.mro())
# print(A.mro())
obj = A()
# print(obj.x)
菱形继承/死亡钻石：一个子类继承的多条分支最终汇聚一个非object的类上
经典类：深度优先
新式类：广度优先
class G: # 在python2中，未继承object的类及其子类，都是经典类
def test(self):
print('from G')
class E(G):
def test(self):
print('from E')
class F(G):
def test(self):
print('from F')
class B(E):
# def test(self):
# print('from B')
pass
class C(F):
def test(self):
print('from C')
class D(G):
def test(self):
print('from D')
class A(B,C,D):
# def test(self):
# print('from A')
pass
obj = A() # A->B->E->C->F->D->G->object
# print(A.mro())
obj.test()
四、多继承的代码规范
以mixin来表示，代表着为这个类添加的功能
# 继承表达式一个is-a的关系
class Vehicle:
pass
class FlyableMixin:
def fly(self):
print('flying')
class CivilAircraft(FlyableMixin,Vehicle):
pass
class Helicopter(FlyableMixin,Vehicle):
pass
class Car(Vehicle):
pass
五、组合
在一个类中以另外一个类的对象作为数据属性，称为类的组合。组合与继承都是用来解决代码的重用性问题。不同的是：继承是一种“是”的关系，比如老师是人、学生是人，当类之间有很多相同的之处，应该使用继承；而组合则是一种“有”的关系，比如老师有生日，老师有多门课程，当类之间有显著不同，并且较小的类是较大的类所需要的组件时，应该使用组合
简述--组合: 一个对象的属性值是指向另外一个类的对象
class People:
school = "虹桥校区"
def __init__(self,name,age,gender):
self.name = name
self.age = age
self.gender = gender
class Student(People):
def choose(self):
print("%s 选课成功" %self.name)
class Teacher(People):
# 空对象,'egon',18,"male",10
def __init__(self,name,age,gender,level):
People.__init__(self,name,age,gender)
self.level = level
def score(self):
print("%s 正在为学生打分" %self.name)
class Course:
def __init__(self,name,price,period):
self.name = name
self.price = price
self.period =period
def tell(self):
print('课程信息<%s:%s:%s>' %(self.name,self.price,self.period))
python = Course("python全栈开发",19800,"6mons")
linux = Course("linux",19000,"5mons")
stu1 = Student("jack",18,"male")
stu2 = Student("tom",19,"male")
stu3 = Student('lili',29,"female")
tea1 = Teacher('egon',18,"male",10) # 空对象,'egon',18,"male",10
tea2 = Teacher('lxx',38,"male",3)
stu1.courses = []
stu1.courses.append(python)
stu1.courses.append(linux)
print(stu1.courses)
for course_obj in stu1.courses:
course_obj.tell()
