Python3.5面向对象程序设计之类的继承和多态详解

来源：jb51　　时间：2019/4/24 12:29:01　　对本文有异议

本文实例讲述了Python3.5面向对象程序设计之类的继承和多态。分享给大家供大家参考，具体如下：

1、继承的定义

继承是指：可以使用现有类的所有功能，并在无需重新编写原来的类的情况下对这些功能进行扩展。
（1）通过继承创建的新类称为“子类”或“派生类”。
（2）被继承的类称为“基类”、“父类”或“超类”。
继承的过程，就是从一般到特殊的过程。要实现继承，可以通过“继承”（Inheritance）和“组合”（Composition）来实现。
在某些 OOP 语言中，一个子类可以继承多个基类。但是一般情况下，一个子类只能有一个基类，要实现多重继承，可以通过多级继承来实现。

2、继承的分类

继承概念的实现方式主要有2类：实现继承、接口继承。

（1）实现继承是指使用基类的属性和方法而无需额外编码的能力；
（2）接口继承是指仅使用属性和方法的名称、但是子类必须提供实现的能力(子类重构父类方法)；
在考虑使用继承时，有一点需要注意，那就是两个类之间的关系应该是“属于”关系。
抽象类仅定义将由子类创建的一般属性和方法。
OO开发范式大致为：划分对象→抽象类→将类组织成为层次化结构(继承和合成) →用类与实例进行设计和实现几个阶段。

3、示例代码

#!/usr/bin/env python
# -*- coding:utf-8 -*-
# Author:ZhengzhengLiu
 
#类的继承
class People:
 def __init__(self,name,age):
  self.name = name
  self.age = age
 
 def eat(self):
  print("%s is eating..." %self.name)
 
 def sleep(self):
  print("%s is sleeping..." %self.name)
 
 def talk(self):
  print("%s is talking..." %self.name)
 
class Man(People):  #继承父类People类
 def make_money(self):
  print("%s is making money..." %self.name)
 
 def sleep(self):
  People.sleep(self)  #对父类方法的扩展
  print("man is sleeping...")
 
class Women(People):
 def shop(self):
  print("%s is shopping..." %self.name)
 
m1 = Man("Jack","20")
m1.eat()
m1.make_money()
m1.sleep()
 
w1 = Women("Amy","25")
w1.talk()
w1.shop()

运行结果：

Jack is eating...
Jack is making money...
Jack is sleeping...
man is sleeping...
Amy is talking...
Amy is shopping...

4、子类中对父类的构造函数进行重构两种方法

#!/usr/bin/env python
# -*- coding:utf-8 -*-
# Author:ZhengzhengLiu
 
#类的继承
#class People:  #经典类
class People(object):  #新式类
 def __init__(self,name,age):
  self.name = name
  self.age = age
 
 def eat(self):
  print("%s is eating..." %self.name)
 
 def sleep(self):
  print("%s is sleeping..." %self.name)
 
 def talk(self):
  print("%s is talking..." %self.name)
 
class Man(People):  #继承父类People类
 def __init__(self,name,age,money):
  #People.__init__(self,name,age)  #(方法一)对构造函数进行重构、添加父类中没有的属性
  super(Man,self).__init__(name,age) #(方法二)利用super对构造函数进行重构（新式类写法）
  self.money = money
  print("%s have money %s$" %(self.name,self.money))
 
 def make_money(self):
  print("%s is making money..." %self.name)
 
 def sleep(self):
  People.sleep(self)  #对父类方法的扩展
  print("man is sleeping...")
 
class Women(People):
 def shop(self):
  print("%s is shopping..." %self.name)
 
m1 = Man("Jack","20",10)
m1.eat()
m1.make_money()
m1.sleep()
 
w1 = Women("Amy","25")
w1.talk()
w1.shop()

运行结果：

J ack have money 10$
Jack is eating...
Jack is making money...
Jack is sleeping...
man is sleeping...
Amy is talking...
Amy is shopping...

5、多继承方式

#!/usr/bin/env python
# -*- coding:utf-8 -*-
# Author:ZhengzhengLiu
 
#类的继承
#class People:  #经典类
class People(object):  #新式类
 def __init__(self,name,age):
  self.name = name
  self.age = age
  self.friends = []
 
 def eat(self):
  print("%s is eating..." %self.name)
 
 def sleep(self):
  print("%s is sleeping..." %self.name)
 
 def talk(self):
  print("%s is talking..." %self.name)
 
class Relationship(object):
 def make_friends(self,obj):
  print("%s is making friends with %s" %(self.name,obj.name))
  self.friends.append(obj)
 
class Man(People,Relationship):  #多继承
 def __init__(self,name,age,money):
  #People.__init__(self,name,age)  #(方法一)对构造函数进行重构、添加父类中没有的属性
  super(Man,self).__init__(name,age) #(方法二)利用super对构造函数进行重构（新式类写法）
  self.money = money
  print("%s have money %s$" %(self.name,self.money))
 
 def make_money(self):
  print("%s is making money..." %self.name)
 
 def sleep(self):
  People.sleep(self)  #对父类方法的扩展
  print("man is sleeping...")
 
class Women(People,Relationship): #多继承
 def shop(self):
  print("%s is shopping..." %self.name)
 
m1 = Man("Jack","20",10)
 
w1 = Women("Amy","25")
 
m1.make_friends(w1)
w1.name = "liu"
print(m1.friends)

运行结果：

Jack have money 10$
Jack is making friends with Amy
[<__main__.Women object at 0x0057FA30>]

6、新式类与经典类的继承顺序

#!/usr/bin/env python
# -*- coding:utf-8 -*-
# Author:ZhengzhengLiu
 
class A(object):		#新式类
 def __init__(self):
  print("A")
 
class B(A):
 def __init__(self):
  
  print("B")
 
class C(A):
 def __init__(self):
  print("C")
 
class D(B,C):
 def __init__(self):
  pass
  #print("D")
 
obj = D()

7、继承示例——学校、教师与学生

#!/usr/bin/env python
# -*- coding:utf-8 -*-
# Author:ZhengzhengLiu
 
#继承实例(新式类)——模拟学校、教师与学生
 
class School(object):
 def __init__(self,name,addr):
  self.name = name
  self.addr = addr
  self.students = []
  self.stuffs = []
 
 def enroll(self,stu_obj):  #学生注册
  print("%s 学员办理注册" %stu_obj.name)
  self.students.append(stu_obj)
 
 def heir(self,staff_obj):  #聘请教师
  print("聘请教师 %s" %staff_obj.name)
  self.stuffs.append(staff_obj)
 
class SchoolMember(object):
 def __init__(self,name,age,sex):
  self.name = name
  self.age = age
  self.sex = sex
 
 def tell(self):
  pass
 
class Teacher(SchoolMember):
 def __init__(self,name,age,sex,salary,course):
  super(Teacher,self).__init__(name,age,sex)
  self.salary = salary
  self.course = course
 
 def tell(self):
  print('''
  ----- info of Teacher:%s -----
  Name:%s
  Age:%s
  Sex:%s
  Salary:%s
  Course:%s
  '''%(self.name,self.name,self.age,self.sex,self.salary,self.course))
 
 def teach(self):
  print("%s is teaching course [%s]" %(self.name,self.course))
 
class Student(SchoolMember):
 def __init__(self,name,age,sex,stu_id,grade):
  super(Student,self).__init__(name,age,sex)
  self.stu_id = stu_id
  self.grade = grade
 
 def tell(self):
  print('''
  ----- info of Student:%s -----
  Name:%s
  Age:%s
  Sex:%s
  Stu_id:%s
  Grade:%s
  '''%(self.name,self.name,self.age,self.sex,self.stu_id,self.grade))
 
 def pay_tuition(self,amount):
  print("%s has paied tuition for $%s" %(self.name,amount))
 
#实例化
school = School("qinghua","beijing")
 
t1 = Teacher("Jack","30","M","20000","Python")
t2 = Teacher("Amy","28","F","15000","Linux")
 
s1 = Student("liu","23","M","1701","Python")
s2 = Student("wang","25","F","1702","Linux")
 
#调用显示学生与教师的信息
t1.tell()
s1.tell()
 
school.heir(t1)  #聘请教师t1
school.enroll(s1) #学生s1注册
school.enroll(s2)
 
print(school.stuffs)
print(school.students)
 
#聘请的第一位教师教课
school.stuffs[0].teach()
for stu in school.students:
 stu.pay_tuition(5000)

运行结果：

        ----- info of Teacher:Jack -----
        Name:Jack
        Age:30
        Sex:M
        Salary:20000
        Course:Python


        ----- info of Student:liu -----
        Name:liu
        Age:23
        Sex:M
        Stu_id:1701
        Grade:Python

聘请教师 Jack
liu 学员办理注册
wang 学员办理注册
[<__main__.Teacher object at 0x0059FDB0>]
[<__main__.Student object at 0x0059FDF0>, <__main__.Student object at 0x0059FE10>]
Jack is teaching course [Python]
liu has paied tuition for $5000
wang has paied tuition for $5000

8、多态（polymorphisn）——一种接口，多种形态

（1）定义

多态性（polymorphisn）是允许你将父对象设置成为和一个或更多的他的子对象相等的技术，

赋值之后，父对象就可以根据当前赋值给它的子对象的特性以不同的方式运作。

简单的说，就是一句话：允许将子类类型的指针赋值给父类类型的指针。

多态的作用：我们知道，封装可以隐藏实现细节，使得代码模块化；继承可以扩展已存在的代码模块（类）；它们的目的都是为了——代码重用。

而多态则是为了实现另一个目的——接口重用！多态的作用，就是为了类在继承和派生的时候，保证使用“家谱”中任一类的实例的某一属性时的正确调用。

Pyhon 很多语法都是支持多态的，比如 len(),sorted(), 你给len传字符串就返回字符串的长度，传列表就返回列表长度。

（2）示例代码：

#!/usr/bin/env python
# -*- coding:utf-8 -*-
# Author:ZhengzhengLiu
 
class Animal(object):
 def __init__(self,name):
  self.name = name
 
 def talk(self):
  raise NotImplementedError("Subclass must implement abstract method")
 
 # 多态——一种接口，多种形态
 @staticmethod
 def animal_talk(obj):
  obj.talk()
 
class Cat(Animal):
 def talk(self):
  print("%s Meow!" %self.name)
 
class Dog(Animal):
 def talk(self):
  print("%s Woof! Woof!" % self.name)
 
d = Dog("A")
#d.talk()
 
c = Cat("B")
#c.talk()
 
#多态
Animal.animal_talk(d)
Animal.animal_talk(c)