json serialization error of "returning" data when update,insert

[exe-dealer]

Traceback (most recent call last): File "./pgblackboard/init.py", line 39, in application yield from app(environ, start_response) File "./pgblackboard/dbapp.py", line 61, in call status, app_iter = handler.handle(cursor) File "./pgblackboard/editing.py", line 58, in handle return '200 OK', [json.dumps(returning_row)] File "/usr/lib/python3.4/json/init.py", line 230, in dumps return _default_encoder.encode(obj) File "/usr/lib/python3.4/json/encoder.py", line 192, in encode chunks = self.iterencode(o, _one_shot=True) File "/usr/lib/python3.4/json/encoder.py", line 250, in iterencode return _iterencode(o, 0) File "/usr/lib/python3.4/json/encoder.py", line 173, in default raise TypeError(repr(o) + " is not JSON serializable") TypeError: datetime.date(2014, 9, 4) is not JSON serializable