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!