Combination and use of python-classes

combination

1. In addition to the inheritance relationship between classes and classes, there is also a combination relationship in python.

What is composition - is resolving one class as a property of another class.

　　　　　　　It is to solve the problem of what a class [has]. eg: Students [have] courses, teachers [have] courses.

The difference between inheritance and composition:

1. Inheritance - "The problem solved: what is [is] what is the relationship: eg students [are] human beings, teachers [are] human beings.

　　　　　　Usage: When there are many identical functions in a class, use the class to extract these functions to form a base class.

2. The problem solved by the combination—": What is the relationship between [there] and what: eg, students [have] courses, teachers [have] courses

　　　　　　Usage: When a class [has] certain functions. eg: Teachers have birthdays, teachers have students.

 

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()

Combination usage

 

Summarize:

Composition is better when the classes are significantly different and the smaller class is a component of the larger class.