Another way of reuse other than inheritance - composition

Combination concept

　　In addition to inheritance, there is another important way of software reuse - composition .

Combination Definition

　　Composition refers to the use of objects (that is, instances) of another class as data attributes in one class, which is called class composition.

　　That is, a property of one class that is an object of another class is composition.

>>> class Equip: #Weapon equipment class 
...      def fire(self):
...         print('release Fire skill')
...
>>> class Riven: #The class of the hero Riven, a hero needs to have equipment, so it needs to combine the Equip class 
... camp= ' Noxus ' 
...      def  __init__ (self,nickname):
...         self.nickname=nickname
... self.equip =Equip() #Use the Equip class to generate an equipment and assign it to the equip attribute of the instance 
... 
 >>> r1=Riven( ' Riven ' )
 >>> r1.equip.fire() #You can use the methods held by the objects generated by the combined classes to 
release Fire skill

Inheritance vs Composition

commonality

　　Both composition and inheritance are important ways to efficiently use existing class resources (code reuse).

difference

　　Inheritance: Establishing the relationship between the derived class and the base class is a "yes" relationship.

　　Composition: The relationship between a class and a composed class is established, which is a "there" relationship.

Applicable

　　Inheritance: When there are many common functions between classes, it is better to use inheritance to extract these common functions and make them into base classes.　　

　　Composition: When the classes are significantly different, and the smaller class is a required component of the larger class, composition is better.

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

class Course:
    def __init__(self,name,period,price):
        self.name=name
        self.period=period
        self.price=price
    def tell_info(self):
        print('<%s %s %s>' %(self.name,self.period,self.price))

class Teacher(People):
    def __init__(self,name,age,sex,job_title):
        People.__init__(self,name,age,sex)
        self.job_title=job_title
        self.course=[]
        self.students=[]


class Student(People):
    def __init__(self,name,age,sex):
        People.__init__(self,name,age,sex)
        self.course=[]


egon =Teacher( ' egon ' ,18, ' male ' , ' Shahe Domineering Gold Medal Teacher ' )
s1 =Student( ' bull grenade ' ,18, ' female ' )

python=Course('python','3mons',3000.0)
linux=Course('python','3mons',3000.0)

#Add courses for teacher egon and student s1 
egon.course.append(python)
egon.course.append(linux)
s1.course.append(python)

#Add student s1 for teacher egon 
egon.students.append(s1)


#使用
for obj in egon.course:
    obj.tell_info()