面向对象（组合）

from math import pi
class Circle:
    def __init__(self,r):
        self.r = r

    def area(self):
        return pi*self.r**2

    def perimeter(self):
        return 2*pi*self.r
c1 = Circle(5)
print(c1.area())       #78.53981633974483
print(c1.perimeter())  #31.41592653589793

from math import pi
class Ring:
    def __init__(self,r1,r2):
        if r1>=r2:
            self.outer = r1
            self.inner = r2
        else:
            self.inner = r1
            self.outer = r2

    def area(self):
        return pi * self.outer ** 2 - pi * self.inner ** 2

    def perimeter(self):
        return 2 * pi * self.outer + 2 * pi * self.inner

r1 = Ring(5,2)
print(r1.area())        #65.97344572538566
print(r1.perimeter())   #43.982297150257104

from math import pi
class Cylinder:
    def __init__(self,r,h):
        self.r = r
        self.h = h

    def area(self):
        c_area = pi * self.r**2
        rec_area = 2 * pi *self.r * self.h
        return c_area*2 + rec_area

    def volume(self):
        c_area = pi * self.r ** 2
        return c_area*self.h

c1 = Cylinder(5,8)
print(c1.area())    #408.4070449666731
print(c1.volume())  #628.3185307179587

什么是耦合？

模块间的依赖性就是耦合，两个功能函数之间的依赖程度

紧耦合：紧耦合就是模块或者系统之间关系太紧密，存在相互调用。紧耦合系统的缺点在于更新一个模块的结果导致其它模块的结果变化，难以重用特定的关联模块。

松耦合通讯机制提供了紧耦合机制所没有的许多优点，并且它们有助于降低客户端和远程服务之间的依赖性。

类的组合

from math import pi
class Circle:
    def __init__(self,r):
        self.r = r

    def area(self):
        return pi*self.r**2

    def perimeter(self):
        return 2*pi*self.r
c= Circle(5)
print(c.area())       #78.53981633974483
print(c.perimeter())  #31.41592653589793

# 圆环类
class Ring:
    def __init__(self,r1,r2):
        c1 = Circle(r1)
        c2 = Circle(r2)
        if r1>=r2:
            self.outer = c1       # 组合
            # self.outer.area()   # c1.area()
            self.inner = c2       # 组合
        else:
            self.inner = c1       # 组合
            self.outer = c2       # 组合

    def area(self):
        return self.outer.area() -self.inner.area()

    def perimeter(self):
        return self.outer.perimeter() + self.inner.perimeter()
r = Ring(5,2)
print(r.area())      #65.97344572538566
print(r.perimeter()) #43.982297150257104

# 圆柱类
class Cylinder:
    def __init__(self,r,h):
        self.c = Circle(r)     # 组合
        self.h = h

    def area(self):
        c_area = self.c.area()
        rec_area = self.c.perimeter() * self.h
        return c_area*2 + rec_area

    def volume(self):
        c_area = self.c.area()
        return c_area*self.h
C = Cylinder(5,8)
print(C.area())   #408.4070449666731
print(C.volume()) #628.3185307179587

组合

    一个类的对象是另一个类对象的属性

    圆形类的对象 是圆环类对象的outer属性的值

 计算圆形相关数据的公式只和Circle类在一起

 其余的用到公式的地方都是通过circle类来使用的

 公式与其他类之间的关系是一个“松耦合”关系

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

    def date(self):
        return '%s-%s-%s'%(self.year,self.month,self.day)
#
class Student:
    def __init__(self,name,num,birth,in_shcool,start_day):
        self.name = name
        self.num = num
        self.birth = birth          # 组合
        self.in_school = in_shcool  # 组合
        self.start_day = start_day  # 组合

d1 = Date(1999,10,27)
d2 = Date(2019,1,9)
d3 = Date(2019,2,9)
alex = Student('alex',10086,d1,d2,d3)
print(alex.birth.year)         #1999
print(alex.birth.month)        #10 
print(alex.birth.day)          #27
print(alex.birth.date())       #1999-10-27

alex.start_day.month +=1
print(alex.start_day.date())   #2019-3-9

class Student:
    def __init__(self,name,num,course):
        self.name = name
        self.num = num
        self.course = course

class Course:
    def __init__(self,name,price,period):
        self.name = name
        self.price = price
        self.period = period
python = Course('python',25000,'6 months')
s1 = Student('alex',10085,python)
s2 = Student('taibai',10084,python)

print(s1.__dict__)        #{'name': 'alex', 'num': 10085, 'course': <__main__.Course object at 0x000001EB9FA5D9E8>}
print(s1.course.price)    #25000
python.price = 30000
python.period = '7 months'

print(s2.course.period)   #7 months