class Person(object):
 __count = 0
 def __init__(self, name):
  Person.__count = Person.__count + 1
  self.name = name
  print Person.__count
 p1 = Person('Bob')
 p1.__count=100
 print p1.__count
 p2 = Person('Alice')

print Person.__count

class Person(object):
 #设置类属性
 __count_of_class = 'original count_of_class'
 def __init__(self, name):
  self.name = name
  print('in class Person : count_of_class = ', Person.__count_of_class,'\n')

#初始化实例p1
p1 = Person('Bob')
#在实例p1上修改属性值
p1.__count_of_class='I\'m not the original count_of_class!'
print('p1\'s _Person__count_of_class = ',p1._Person__count_of_class)
print('p1\'s __count_of_class = ',p1.__count_of_class,'\n')

#在类Person上修改属性值
Person.__count_of_class = 'I\'m not the original count_of_class!'
#将这句注释取消掉，会发现真正的私有属性的值也改变了
#Person._Person__count_of_class = 'I\'m not the original count_of_class!'
print('Person\'s _Person__count_of_class = ',Person._Person__count_of_class)
print('Person\'s __count_of_class = ',Person.__count_of_class)

in class Person : count_of_class = original count_of_class

p1's _Person__count_of_class = original count_of_class
p1's __count_of_class = I'm not the original count_of_class!

Person's _Person__count_of_class = original count_of_class
Person's __count_of_class = I'm not the original count_of_class!

"""
取消掉
##Person._Person__count_of_class = 'I\'m not the original count_of_class!'
的注释，输出结果：
"""

in class Person : count_of_class = original count_of_class 
p1's _Person__count_of_class = original count_of_class 
p1's __count_of_class = I'm not the original count_of_class! 

#注意这一句：
Person's _Person__count_of_class = I'm not the original count_of_class! 
Person's __count_of_class = I'm not the original count_of_class!

class Person(object):
 pass

p1=Person()
#给p1创建属性new_of_instance
p1.new_of_instance = 'I\'m new in p1!'
print(p1.new_of_instance)

#给Person类创建属性new_of_class
Person.new_of_class = 'I\'m new in Person!'

#在类中新加的属性，可以通过实例来访问
print(p1.new_of_class)


>输出：
I'm new in p1!
I'm new in Person!