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。

组合和继承都是有效利用已有类的资源的重要方式。区别：

继承：通过继承建立了派生类和基类之间的关系，是一种“是”的关系。当类之间有很多相同的功能，提取这些共同的功能做成基类，用继承比较好。例如：学生是人，老师是人。

组合：用组合的方式建立了类与组合之间的关系，是一种“有”的关系。例如：人有生日，老师有课程

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，用组合比较好。

class People:
    school = "university"

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

class Teacher(People):       # 继承
    def __init__(self,name,age,sex,level,salary):
        super(Teacher, self).__init__(name,age,sex)
        self.level = level
        self.salary = salary

    def teach(self):
        print("%s is teaching"%self.name)


class Student(People):
    def __init__(self, name, age, sex, class_time):
        super(Student, self).__init__(name,age,sex)
        self.class_time = class_time

    def learn(self):
        print("%s is learning" % self.name)

class Course:
    def __init__(self,name,price,period):
        self.course_name = name
        self.course_price = price
        self.course_period = period

    def tell_info(self):
        print("课程名：%s，课程价钱：%s，课程周期：%s"%(self.course_name,self.course_price,self.course_period))

class Date():
    def __init__(self,year,mon,day):
        self.year = year
        self.mon = mon
        self.day = day

    def tell_info(self):
        print("%s-%s-%s"%(self.year,self.mon,self.day))


# teacher1  = Teacher("alex",20,"male",10,3000)
# python = Course("python",3000,"3months")
# linux = Course("linux",2000,"4months")
#
# teacher1.course = python    # 让老师有了一个属性，指向课程

# print(teacher1.course.course_name)
# teacher1.course.tell_info()
#
# student = Student("张三",28,"female","8:00")
# student.course1 = python
# student.course2 = linux
# student.course1.tell_info()
# student.course2.tell_info()
# student.courses=[]
# student.courses.append(python)
# student.courses.append(linux)
# for i in student.courses:
#     print(i.__dict__)

student = Student("张三",28,"female","8:00")
d = Date(1988,4,20)
student.birth = d    # 组合
student.birth.tell_info()