ValueError('No JSON object could be decoded',) is not JSON serializable

Question

My code is fetching facebook information I will get this error

Traceback (most recent call last):
  File "crawler.py", line 34, in <module>
    print graph.get_information(url[i]).encode('utf-8')
  File "/weblog/workingspace/thun/facebook-api/facebook_api.py", line 23, in get_information
    return json.dumps(ret)
  File "/usr/lib64/python2.6/json/__init__.py", line 230, in dumps
    return _default_encoder.encode(obj)
  File "/usr/lib64/python2.6/json/encoder.py", line 367, in encode
    chunks = list(self.iterencode(o))
  File "/usr/lib64/python2.6/json/encoder.py", line 306, in _iterencode
    for chunk in self._iterencode_list(o, markers):
  File "/usr/lib64/python2.6/json/encoder.py", line 204, in _iterencode_list
    for chunk in self._iterencode(value, markers):
  File "/usr/lib64/python2.6/json/encoder.py", line 309, in _iterencode
    for chunk in self._iterencode_dict(o, markers):
  File "/usr/lib64/python2.6/json/encoder.py", line 275, in _iterencode_dict
    for chunk in self._iterencode(value, markers):
  File "/usr/lib64/python2.6/json/encoder.py", line 317, in _iterencode
    for chunk in self._iterencode_default(o, markers):
  File "/usr/lib64/python2.6/json/encoder.py", line 323, in _iterencode_default
    newobj = self.default(o)
  File "/usr/lib64/python2.6/json/encoder.py", line 344, in default
    raise TypeError(repr(o) + " is not JSON serializable")
TypeError: ValueError('No JSON object could be decoded',) is not JSON serializable

My code is:

print graph.get_information("name of user").encode('utf-8')

I don't know what wrong because when i use https://developers.facebook.com/tools/explorer to get information. It's work But when I use facebook-api i got some error. Please help me. Thank you for your attention.

Ps. Sorry about my bad English

Answer 1

The error says "Some Type is not JSON serializable" that means the data you are getting from facebook contains a datatype which is not supported by JSON. Following datatypes are supported by JSON

• Primitive Types
  • String
  • Number
  • Boolean
  • Null
• Structure Type
  • Object
  • Array

The code which is actually converting the data into JSON (in your case facebook_api.py) needs to handle this problem. You can write a custom json encoder that will handle all datatypes which are not supported by JSON. for eg

class CustomJSONEncoder(json.JSONEncoder):
    def default(self, obj):
        if isinstance(obj, decimal.Decimal):
            return float(obj)
        if isinstance(obj, date):
            return obj.isoformat()
        else:
            return super(CustomJSONEncoder, self).default(obj)

In the above code I am handling 'decimal' and 'date' datatypes which are not supported by JSON. Then you need to use this custome JSON encoder in your call to 'json.dumps'

json.dumps(input_dict, cls=CustomJSONEncoder)