day6面向对象--继承、多态

继承

    继承：就像遗传一样，继承就是拥有父类的所有方法和属性，并且能够定义自己独特的属性和方法，对上面的类进行扩展。

可以什么都不写，直接继承父类，如下：

class People(object):

    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):
    pass

class Woman(People):
    pass

m1 = Man("chenronghua",)
m1.eat()
运行结果如下：
chenronghua is eating......

上面代码可以看出，首先定义了一个People的类，还有一个Man(People)类直接继承People类。

下面，我们在上面的Man()类中定义一个单独的方法，如下：

class People(object):

    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):
    def piao(self):
        print("%s is piaoing......20s......" %self.name)

class Woman(People):
    pass

m1 = Man("chenronghua",)
m1.piao()
运行结果如下：
chenronghua is piaoing......20s......

上面，我们给Man()增加了新的方法，可以看出，能够执行。

下面，我们来重写父类。扩展新功能，子类并且要具有父类的所有方法与属性。在子类中调用父类：

class People(object):

    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):
    def piao(self):
        print("%s is piaoing......20s......" %self.name)

    def sleep(self):
        People.sleep(self)
        print("man is sleeping......")

class Woman(People):
    pass

m1 = Man("chenronghua",)
m1.sleep()

上面代码中，子类调用了父类中的方法，要明白本质，创建实例的本质是增加了一个新的内存变量。

不同类中方法的调用：

class People(object):

    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):
    def piao(self):
        print("%s is piaoing......20s......" %self.name)

    def sleep(self):
        People.sleep(self)
        print("man is sleeping......")

class Woman(People):

    def get_birth(self):
        print("%s is borning a bady......" %self.name)

# m1 = Man("chenronghua",)
# m1.sleep()

w1 = Woman("chenronghua",)
w1.get_birth()
w1.piao()
运行如下：
chenronghua is borning a bady......
Traceback (most recent call last):
  File "/home/zhuzhu/第六天/inherit.py", line 34, in <module>
    w1.piao()
AttributeError: 'Woman' object has no attribute 'piao'

从上面可以看出，继承同一个父类的子类是方法是不能相互调用的。

class People(object):

    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):
    def __init__(self,name,age,money):     #给男的单独增加属性
        People.__init__(self,name,age)
        self.money = money
        print("%s 刚出生就有%s元" %(self.name,self.money))    #构造函数的时候就会执行代码

    def piao(self):
        print("%s is piaoing......20s......" %self.name)

    def sleep(self):
        People.sleep(self)
        print("man is sleeping......")

class Woman(People):

    def get_birth(self):
        print("%s is borning a bady......" %self.name)

m1 = Man("chenronghua",,)
m1.sleep()
运行结果如下：
chenronghua 刚出生就有100元
chenronghua is sleeping.....
man is sleeping.....

从上面代码可以看出，__init__(self,name,age,money)类的初始化，People.__init__(self,name,age)继承，继承父类的属性，普通的继承。

下面来看看新式类中的继承。

class People(object):

    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):
    def __init__(self,name,age,money):     #给男的单独增加属性
        super(Man,self).__init__(name,age)
        self.money = money
        print("%s 刚出生就有%s元" %(self.name,self.money))    #构造函数的时候就会执行代码

    def piao(self):
        print("%s is piaoing......20s......" %self.name)

    def sleep(self):
        People.sleep(self)
        print("man is sleeping......")

class Woman(People):

    def get_birth(self):
        print("%s is borning a bady......" %self.name)

m1 = Man("chenronghua",,)
m1.sleep()

新式类是用super()函数来实现继承的，super(Man,self).__init__(name,age)实现继承，新式类和旧式类的差别主要体现在多继承上面。

下面看下类的多继承问题：

class People(object):

    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 Relation(object):

    def make_friends(self,obj):
        print("%s is making friends with %s" %(self.name,obj.name))

class Man(People,Relation):
    def __init__(self,name,age,money):     #给男的单独增加属性
        super(Man,self).__init__(name,age)    #超级父类，Man继承父类name,age
        self.money = money
        print("%s 刚出生就有%s元" %(self.name,self.money))    #构造函数的时候就会执行代码

    def piao(self):
        print("%s is piaoing......20s......" %self.name)

    def sleep(self):
        People.sleep(self)
        print("man is sleeping......")

class Woman(People,Relation):

    def get_birth(self):
        print("%s is borning a bady......" %self.name)

w1 = Woman("ruhua",)

m1 = Man("chenronghua",,)
m1.make_friends(w1)           #把w1实例当做参数传给make_friends，等价于obj》w1，obj.name》w1.name

上面代码中，当子类继承多个父类的时候，即便其中一个父类没有实例化，也能调用另外一个父类的方法和属性。通过子类把两个父类关联到一起。

    多态

一个接口，多个重用