Python之道–实例和类的继承以及运算符重载

Python版本：2.7.4

主机环境：Gentoo with Linux Kernel 3.4.36

原创作品，转载请标明：http://blog.geekcome.com/archives/79

Python中关于类和实例的关系比JAVA，C++等语言中的类之间的关系要简单的多。对于学过C++或JAVA语言的我们，类和对象已经很熟悉了，他们的设计思想似乎也已经融入了我们的身体，这里不再多说他们的概念。

这里只是展示几个Python的类的实例，用来说明Python中的类和实例以及类的继承。

下面的实例有三个类：FirstClass,SecondClass,ThordClass

class FirstClass:
    def setdata(self,value):
        self.data = value
    def __init__(self,value):
        self.data = value
    def display(self):
        print self.data

        
class SecondClass(FirstClass):
    def display(self):
        print ‘Current value is %s’ % self.data

        
class ThirdClass(SecondClass):
    def __add__(self,other):
        return ThirdClass(self.data + other)
    def __str__(self):
        return ‘ThirdClass: %s’ % self.data
    def mul(self,value):
        self.data *= value

三个类的定义如上面所示，FirstClass是基类，SecondClass继承了FirstClass，而ThirdClass又继承了SecondClass。

a = FirstClass(“First Class”)
a.display()
a.setdata(‘Again First Class’)
a.display()

b = SecondClass(‘Second Class’)
b.display()
b.setdata(‘Again Second Class’)
b.display()

c = ThirdClass(“Third Class”)
c.display()
c = c + ‘ Again’
c.display()
c.mul(8)
print c

第三个类中通过定义__**__函数来重载了加法运算，重载了print打印字符串的内置函数str() 。函数的运行结果如下：

First Class
Again First Class
Current value is Second Class
Current value is Again Second Class
Current value is Third Class
Current value is Third Class Again
ThirdClass: Third Class AgainThird Class AgainThird Class AgainThird Class AgainThird Class AgainThird Class AgainThird Class AgainThird Class Again