使用类与对象的变量

#!/usr/bin/python
#Filename:objvar.py


class Person:
    '''Represents a person.'''
    population=0


    def __init__(self,name):
        '''Initializes the person's data.'''
        self.name=name
        print '(Initializing %s)' % self.name


        #when this person is created, he/she
        #adds to the population
        Person.population += 1


    def __del__(self):
        '''I am dying.'''
        print '%s says bye.' %self.name


        Person.population -= 1


        if Person.population==0:
           print 'I am the last one.'
        else:
            print'There are still %d people left.' % Person.population


            
    def sayHi(self):
        '''Greeting by the person. Really, that's all it does.'''
        print 'Hi,my name is %s.' % self.name




    def howMany(self):
        '''Prints the current population.'''
        if Person.population==1:
            print' I am the only person here.'
        else:
            print'We have %d persons here.' % Person.population




swaroop=Person('Swaroop')
swaroop.sayHi()
swaroop.howMany()


kalam=Person('Abdulkalam')
kalam.sayHi()
kalam.howMany()


swaroop.sayHi()
swaroop.howMany()


del kalam 

del swaroop

书上的代码可能有问题，最后两行是自己添上的。

类的变量 由一个类的所有对象（实例）共享使用，虽然对象的变量有相同的名称，但是是互不相关的，互不共享的。