动态修改类的属性

from __future__ import nested_scopes
import new
def enhance_method(klass, method_name, replacement):
    '替换方法的函数'
    method = getattr(klass, method_name)
    setattr(klass, method_name, new.instancemethod(
        lambda *args, **kwds: replacement(method, *args, **kwds), None, klass))

def method_logger(old_method, self, *args, **kwds):
    '需要更的新方法'， 

　 做一些修改
    somting.........

　　返回旧方法的返回值
    return_value = old_method(self, *args, **kwds) # call the original method
    return return_value
def demo():
    class Deli:
        def order_cheese(self, cheese_type):
            print 'Sorry, we are completely out of %s' % cheese_type
    d = Deli()
    d.order_cheese('Gouda')

    # 调用函数更新方法
    enhance_method(Deli, 'order_cheese', method_logger)

    d.order_cheese('Cheddar')

当需要修改第三方python包的某个类的某个方法时，这种修改方式非常有用