如何解决python json错误xx is not json serializabke的问题？

#!/usr/bin/env python 
# -*- coding: utf-8 -*- 
#json_extention 
#2014-03-16 
#copyright: orangleliu 
#license: BSD 
 
''''' 
python中dumps方法很好用，可以直接把我们的dict直接序列化为json对象 
但是有的时候我们加了一些自定义的类就没法序列化了，这个时候需要 
自定义一些序列化方法 
 
参考： 
http://docs.python.org/2.7/library/json.html 
 
例如: 
In [3]: from datetime import datetime 
 
In [4]: json_1 = {'num':1112, 'date':datetime.now()} 
 
In [5]: import json 
 
In [6]: json.dumps(json_1) 
--------------------------------------------------------------------------- 
TypeError         Traceback (most recent call last) 
D:\devsofts\python2.7\lib\site-packages\django\core\management\commands\shell.py 
c in <module>() 
----> 1 json.dumps(json_1) 
 
TypeError: datetime.datetime(2014, 3, 16, 13, 47, 37, 353000) is not JSON serial 
izable 
''' 
 
from datetime import datetime 
import json 
 
class DateEncoder(json.JSONEncoder ): 
 def default(self, obj): 
  if isinstance(obj, datetime): 
   return obj.__str__() 
  return json.JSONEncoder.default(self, obj) 
 
json_1 = {'num':1112, 'date':datetime.now()} 
print json.dumps(json_1, cls=DateEncoder) 
 
''''' 
输出结果： 
 
PS D:\code\python\python_abc> python .\json_extention.py 
{"date": "2014-03-16 13:56:39.003000", "num": 1112} 
''' 
 
#我们自定义一个类试试 
class User(object): 
 def __init__(self, name): 
  self.name = name 
 
class UserEncoder(json.JSONEncoder): 
 def default(self, obj): 
  if isinstance(obj, User): 
   return obj.name 
  return json.JSONEncoder.default(self, obj) 
 
json_2 = {'user':User('orangle')} 
print json.dumps(json_2, cls=UserEncoder) 
 
''''' 
PS D:\code\python\python_abc> python .\json_extention.py 
{"date": "2014-03-16 14:01:46.738000", "num": 1112} 
{"user": "orangle"} 
 
'''