动态修改Python类和实例的方法（转）

class Dog:
    def bark(self):
        print ‘Woof!‘
 
class Husky(Dog):
    def bark(self)
        print ‘Howl!‘

def newbark(self):
    print ‘Wrooof!‘
 
def howl(self):
    print ‘Howl!‘
 
# Replace an existing method
Dog.bark = newbark
 
# Add a new method
Dog.howl = howl

def herd(self, sheep):
    self.run()
    self.bark()
    self.run()
 
border_collie = Dog()
border_collie.herd = herd

border_collie.herd(sheep)
 
TypeError: herd() takes exactly 2 arguments (1 given)
The problem with the previous code is that the herd is not a bound method, just take a look at the following code:
 
print border_collie.herd
 
<function herd at 0xf9c5f0>

import types
 
border_collie = Dog()
border_collie.herd  = types.MethodType(herd, border_collie)
 
print border_collie.herd
<bound method ?.herd of <__main__.Dog instance at 0x23c9518>>
 
border_collie.herd(sheep)