python - 如何扩充 Python 对象的方法？

Question

我有一个垃圾邮件对象列表:

class Spam:
    def update(self):
        print('updating spam!')

其中一些可能是 SpamLite 对象:

class SpamLite(Spam):
    def update(self):
        print('this spam is lite!')
        Spam.update(self)

我希望能够从列表中获取任意对象，并向它的更新方法添加一些内容，例如:

def poison(spam):
    tmp = spam.update 
    def newUpdate(self):
        print 'this spam has been poisoned!'
        tmp(self)
    spam.update = newUpdate

我希望 spam.update() 现在打印:

this spam has been poisoned!
updating spam!

或

this spam has been poisoned!
this spam is lite!
updating spam!

取决于它是 SpamLite 还是垃圾邮件。

但这不起作用，因为 spam.update() 不会自动传入 self 参数，并且因为如果 tmp 离开作用域或发生更改，那么它不会调用旧的更新。我有办法做到这一点吗？

Answer 1

def poison(spam):
    tmp = spam.update
    def newUpdate():
        print 'this spam has been poisoned!'
        tmp()
    spam.update = newUpdate

完整脚本:

class Spam:
    def update(self):
        print('updating spam!')

class SpamLite(Spam):
    def update(self):
        print('this spam is lite!')
        Spam.update(self)

def poison(spam):
    tmp = spam.update # it is a bound method that doesn't take any arguments
    def newUpdate():
        print 'this spam has been poisoned!'
        tmp()
    spam.update = newUpdate


from operator import methodcaller    
L = [Spam(), SpamLite()]
map(methodcaller('update'), L)
map(poison, L)
print "*"*79
map(methodcaller('update'), L)

输出:

updating spam!this spam is lite!updating spam!*******************************************************************************this spam has been poisoned!updating spam!this spam has been poisoned!this spam is lite!updating spam!