python中json对象转换出错解决方法【转】

s={"username":"admin","password":"password","tenantid":""}

import json
>>> a=json.loads(s)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/lib/python2.7/json/__init__.py", line 326, in loads
    return _default_decoder.decode(s)
  File "/usr/lib/python2.7/json/decoder.py", line 366, in decode
    obj, end = self.raw_decode(s, idx=_w(s, 0).end())
TypeError: expected string or buffer
>>>

>>> s={"username":"admin","password":"password","tenantid":""}
>>> print s
{'username': 'admin', 'password': 'password', 'tenantid': ''}

json_string=json.dumps(s)
python_obj=json.loads(json_string)