Learning-Python【24】：面向对象之组合

组合的概念

一个类的对象具备某一个属性，该属性的值是来自于另外一个类的对象，称之为组合，组合也是用来解决类与类之间代码冗余的问题

组合的使用

在继承中，举了一个属性查找顺序方式一的例子，最终的实现成果如下

class People():
    school = '湫兮如风学院'

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

class Student(People):

    def __init__(self, name, age, gender, stu_id):
        People.__init__(self, name, age, gender)
        self.stu_id = stu_id

    def choose_course(self):
        print('%s正在选课' %self.name)

class Teacher(People):

    def __init__(self, name, age, gender, level, salary):

        People.__init__(self, name, age, gender)
        self.level = level
        self.salary = salary

    def score(self, stu, num):
        print('教师%s给学生%s打%s分' %(self.name, stu.name, num))
        stu.num = num

stu = Student('qiu', 22, 'male')
tea = Teacher('xi', 20, 'male', 10, 3000)

现在学生有课程信息，课程价格，课程周期，教师也有相同的信息，于是添加相应的数据属性，注意这里不能将这些信息放到对应的类里面，假如我将一门课程放入学生类，那当我实例化一个学生对象时，他只能学习这门课程，如果我有多个课程呢？所以这些信息是对象独有的，并不是公有的

class People():
    school = '湫兮如风学院'

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

class Student(People):

    def __init__(self, name, age, gender, stu_id, course_name, course_period, course_price):
        People.__init__(self, name, age, gender)
        self.stu_id = stu_id

        self.course_name = course_name
        self.course_period = course_period
        self.course_price = course_price

    def choose_course(self):
        print('%s正在选课' %self.name)

class Teacher(People):

    def __init__(self, name, age, gender, level, course_name, course_period, course_price):
        People.__init__(self, name, age, gender)
        self.level = level

        self.course_name = course_name
        self.course_period = course_period
        self.course_price = course_price

    def score(self, stu, num):
        stu.score = num
        print('教师%s给学生%s打%s分' % (self.name, stu.name, num))

但这样写出来你会发现，代码又有重复部分了，可以考虑将课程信息放到父类 People，但并不合理，并不是所有 “湫兮如风学院” 的人都有这些课程信息，如果还有个管理员，他并不需要这些课程信息。还有教师与学生都属于 “湫兮如风学院” 的人，这是一个从属关系，可以使用继承，但课程与老师、课程与学生之间没有从属关系，仅仅是老师和学生有课程这种属性。所以此时考虑再定义一个类，用来存放课程信息，并实例化出两门课程

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

class People():
    school = '湫兮如风学院'

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

class Student(People):

    def __init__(self, name, age, gender, stu_id):
        People.__init__(self, name, age, gender)
        self.stu_id = stu_id

    def choose_course(self):
        print('%s正在选课' %self.name)

class Teacher(People):

    def __init__(self, name, age, gender, level):
        People.__init__(self, name, age, gender)
        self.level = level

    def score(self, stu, num):
        stu.score = num
        print('教师%s给学生%s打%s分' % (self.name, stu.name, num))

python = Course('Python全栈开发', '5 months', 3000)
linux = Course('linux运维', '5 months', 2000)

这时课程与学生、课程与老师之间还没有建立关系，所以要做建立关系的操作

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

class People():
    school = '湫兮如风学院'

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

class Student(People):

    def __init__(self, name, age, gender, stu_id):
        People.__init__(self, name, age, gender)
        self.stu_id = stu_id

    def choose_course(self):
        print('%s正在选课' %self.name)

class Teacher(People):

    def __init__(self, name, age, gender, level):

        People.__init__(self, name, age, gender)
        self.level = level

    def score(self, stu, num):
        stu.score = num
        print('教师%s给学生%s打%s分' % (self.name, stu.name, num))

# 创建课程
python = Course('Python全栈开发', '5 months', 3000)
linux = Course('linux运维', '5 months', 2000)

# 创建学生和老师
stu1 = Student('夕颜', 19, 'male', 1001)
tea1 = Teacher('东风', 19, 'female', 10)

# 将学生、老师与课程对象关联
stu1.course = python
tea1.course = linux

# 查看学生和老师的课程，
print(stu1.course)
print(tea1.course)

# 运行
<__main__.Course object at 0x000002081E998D68>
<__main__.Course object at 0x000002081E998DA0>

建立了关系，便可以查看学生与老师的课程信息，但上面的输出操作并不能查看到学生选了哪门课程，老师选了哪门课程，查看的并不是课程的详细信息，于是需要进一步访问学生课程信息的课程名、课程周期、课程价格，同样老师的课程信息也需要进一步才能访问

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

class People():
    school = '湫兮如风学院'

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

class Student(People):

    def __init__(self, name, age, gender, stu_id):
        People.__init__(self, name, age, gender)
        self.stu_id = stu_id

    def choose_course(self):
        print('%s正在选课' %self.name)

class Teacher(People):

    def __init__(self, name, age, gender, level):

        People.__init__(self, name, age, gender)
        self.level = level

    def score(self, stu, num):
        stu.score = num
        print('教师%s给学生%s打%s分' % (self.name, stu.name, num))

# 创建课程
python = Course('Python全栈开发', '5个月', 3000)
linux = Course('linux运维', '5个月', 2000)

# 创建学生和老师
stu1 = Student('夕颜', 19, 'male', 1001)
tea1 = Teacher('东风', 19, 'female', 10)

# 将学生、老师与课程对象关联
stu1.course = python
tea1.course = linux

# 查看学生和老师的课程
print(stu1.course.course_name, stu1.course.course_period, stu1.course.course_price)
print(tea1.course.course_name, tea1.course.course_period, tea1.course.course_price)

# 运行
Python全栈开发 5个月 3000
linux运维 5个月 2000

这样确实能够访问到课程的详细信息，但是你会发现，我做了同样的事情，每次都要先去访问课程才能访问到课程的详细信息，于是可以考虑将课程的详细信息作为一个功能（函数），每次访问通过学生的课程或老师的课程去访问，也就是说把学生的课程或老师的课程当作参数传入这个函数，然后再去访问课程的详细信息

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

class People():
    school = '湫兮如风学院'

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

class Student(People):

    def __init__(self, name, age, gender, stu_id):
        People.__init__(self, name, age, gender)
        self.stu_id = stu_id

    def choose_course(self):
        print('%s正在选课' %self.name)

class Teacher(People):

    def __init__(self, name, age, gender, level):

        People.__init__(self, name, age, gender)
        self.level = level

    def score(self, stu, num):
        stu.score = num
        print('教师%s给学生%s打%s分' % (self.name, stu.name, num))

# 创建课程
python = Course('Python全栈开发', '5个月', 3000)
linux = Course('linux运维', '5个月', 2000)

# 创建学生和老师
stu1 = Student('夕颜', 19, 'male', 1001)
tea1 = Teacher('东风', 19, 'female', 10)

# 将学生、老师与课程对象关联
stu1.course = python
tea1.course = linux

def tell_info(course_obj):
    print(course_obj.course_name, course_obj.course_period, course_obj.course_price)

# 查看学生和老师课程的详细信息
tell_info(stu1.course)
tell_info(tea1.course)

这时便不需要做同样的事情了，每次只需要传入一个课程对象，但是在调用的时候都是手动去传入课程对象，我现在想实现的是让它自动传入一个课程对象，于是将它放入课程类中，通过 self 自动传入，然后课程对象就可以调用这个功能去查看课程的相关信息

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

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

class People():
    school = '湫兮如风学院'

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

class Student(People):

    def __init__(self, name, age, gender, stu_id):
        People.__init__(self, name, age, gender)
        self.stu_id = stu_id

    def choose_course(self):
        print('%s正在选课' %self.name)

class Teacher(People):

    def __init__(self, name, age, gender, level):

        People.__init__(self, name, age, gender)
        self.level = level

    def score(self, stu, num):
        stu.score = num
        print('教师%s给学生%s打%s分' % (self.name, stu.name, num))

# 创建课程
python = Course('Python全栈开发', '5个月', 3000)
linux = Course('linux运维', '5个月', 2000)

# 通过课程对象去查看课程的详细信息
python.tell_info()
linux.tell_info()

# 创建学生和老师
stu1 = Student('夕颜', 19, 'male', 1001)
tea1 = Teacher('东风', 19, 'female', 10)

# 将学生、老师与课程对象关联
stu1.course = python
tea1.course = linux

学生和老师也可以通过所选的课程去访问该课程的详细信息

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

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

class People():
    school = '湫兮如风学院'

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

class Student(People):

    def __init__(self, name, age, gender, stu_id):
        People.__init__(self, name, age, gender)
        self.stu_id = stu_id

    def choose_course(self):
        print('%s正在选课' %self.name)

class Teacher(People):

    def __init__(self, name, age, gender, level):

        People.__init__(self, name, age, gender)
        self.level = level

    def score(self, stu, num):
        stu.score = num
        print('教师%s给学生%s打%s分' % (self.name, stu.name, num))

# 创建课程
python = Course('Python全栈开发', '5个月', 3000)
linux = Course('linux运维', '5个月', 2000)

# 通过课程对象去查看课程的详细信息
# python.tell_info()
# linux.tell_info()

# 创建学生和老师
stu1 = Student('夕颜', 19, 'male', 1001)
tea1 = Teacher('东风', 19, 'female', 10)

# 将学生、老师与课程对象关联
stu1.course = python
tea1.course = linux

# 学生和老师所选课程的详细信息
stu1.course.tell_info()
tea1.course.tell_info()

# 运行
课程名: Python全栈开发 | 课程周期: 5个月 | 课程价格: 3000
课程名: linux运维 | 课程周期: 5个月 | 课程价格: 2000

以上就是组合的应用，让一个类的对象具备一个属性，这个属性的值来自于另外一个类的对象，这就是把两个类组合到一起