Python __getattr__与__setattr__使用方法

比如下面的例子：

class Book ( object ):
    def __setattr__ ( self , name , value ):
        if name == 'value' :
            object . __setattr__ ( self , name , value - 100 )
        else :
            object . __setattr__ ( self , name , value )
    def __getattr__ ( self , name ):
        try :
            return object . __getattribute__ ( name )
        except :
            return name + ' is not found!'
    def __str__ ( self ):
        return self . name + ' cost : ' + str ( self . value )

c = Book ()
c . name = 'Python'
c . value = 100
print c . name
print c . value
print c
print c . Type

上面的例子中，在赋值书的value属性时，偷偷的将value减去了１００，呵。输出结果：

Python
0
Python cost : 0
Type is not found!