多态与多态性

什么是多态,什么是多态性

多态是指一类事物的多种形态,例如:动物类(猪,狗,人...)

多态性是指在不考虑实例的情况下使用实例

多态性的好处

1. 增加了程序的灵活性
2. 增加了程序额可拓展性

多态基础

class Animal:
    def speak(self):
        pass

class Pig(Animal):
    def speak(self):
        print('哼哼哼')

class Dog(Animal):
    def speak(self):
        print('汪汪')

class People(Animal):
    def speak(self):
        print('say hello')

pig=Pig()
dog=Dog()
people=People()
# pig.speak()
# dog.speak()
# people.speak()

def animal_speak(obj):
    obj.speak()
animal_speak(pig)
animal_speak(people)

#第一种方式:用abc实现接口统一化,约束代码(用的比较少)
import abc
#第一在括号中写metaclass=abc.ABCMeta
class Animal(metaclass=abc.ABCMeta):
    #第二在要约束的方法上,写abc.abstractmethod装饰器
    @abc.abstractmethod
    def speak(self):
        pass

class Pig(Animal):
    def speak(self):
        print('哼哼哼')
class Dog(Animal):
    def yy(self):
        print('汪汪')

class People(Animal):
    def zz(self):
        print('say hello')


people = People()
people.zz()
# 这样就不能利用多态性
def animal_speak(obj):
    obj.speak()
pig=Pig()

#第二种方式,用异常处理来实现(常用)
class Animal():
    def speak(self):
        #主动抛出异常
        raise Exception('你得给我重写它啊')
class Pig(Animal):
    def speak(self):
        print('哼哼哼')
class People(Animal):
    def speak(self):
        print('say hello')
pig=Pig()
pe=People()
def animal_speak(obj):
    obj.speak()

animal_speak(pig)
animal_speak(pe)

python中鸭子类型

Python崇尚鸭子类型，即‘如果看起来像、叫声像而且走起路来像鸭子，那么它就是鸭子

class Pig:
    def speak(self):
        print('哼哼哼')
class People:
    def speak(self):
        print('say hello')

pig=Pig()
pe=People()
def animal_speak(obj):
    obj.speak()
animal_speak(pig)
animal_speak(pe)

传统写法
class File:
    def read(self):
        pass
    def write(self):
        pass
#内存类
class Memory(File):
    def read(self):
        print('Memory...read')
    def write(self):
        print('Memory...write')

class Network(File):
    def read(self):
        print('Network...read')
    def write(self):
        print('Network...write')

鸭子类型写法
 内存类
class Memory:
    def read(self):
        print('Memory...read')

    def write(self):
        print('Memory...write')

class Network:
    def read(self):
        print('Network...read')

    def write(self):
        print('Network...write')

def read(obj):
    obj.read()
m=Memory()
n=Network()
read(m)
read(n)