I am using the python package pymongo to retrieve data from a mongodb database.

>>> r = collection.find()   # returns an object of class 'Cursor'

Then I convert to a list

>>> l = list(r)             # returns a 'list' of 'dict'

here is what print(l) returns:

>>> [{u'date': datetime.datetime(2009, 11, 10, 10, 45), u'_id': 1, u'name': u'name1', u'value': 11},{u'date': datetime.datetime(2013, 11, 10, 10, 45), u'_id': 2, u'name': u'name2', u'value': 22}]

Now I need to convert to JSON so that I can manipulate it.

>>> json.dumps(l)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/lib/python2.7/json/__init__.py", line 231, in dumps
    return _default_encoder.encode(obj)
  File "/usr/lib/python2.7/json/encoder.py", line 201, in encode
    chunks = self.iterencode(o, _one_shot=True)
  File "/usr/lib/python2.7/json/encoder.py", line 264, in iterencode
    return _iterencode(o, 0)
  File "/usr/lib/python2.7/json/encoder.py", line 178, in default
    raise TypeError(repr(o) + " is not JSON serializable")
TypeError: datetime.datetime(2009, 11, 12, 11, 14) is not JSON serializable

I have also tried to follow http://api.mongodb.org/python/1.7/api/pymongo/json_util.html without success:
Edit: the recent version of the link is http://api.mongodb.org/python/current/api/bson/json_util.html

>>> json.dumps(l, default=json_util.default)  
Traceback (most recent call last):  
  File "<stdin>", line 1, in <module>  
NameError: name 'json_util' is not defined  

Note: precisely I need to push this result to R using the R package rPython and its function rPython::python.get(“l”)

Side Question: What is the u (u’Date’, u’name’, etc..) before each field in the list of dict?

The pymongo documentation you pointed is obsolete. If you’re using version 1.7 I recommend updating. With a more recent version you can do this:

from bson.json_util import dumps



Side answer: u'name', u'date', u'_id' etc are the names of the fields of the document on the database.

from bson import json_util


In my situation, this error is due to mongo DB id object in flask
all you have to do is convert id (NOTE: if you need id convert it else you can pop it too)
I’m sharing my solution which I figured out hope this helps someone

from flask import jsonify

def get_data(self,data):
     data['_id'] = str(data['_id'])
     return data

app =  Flask(__name__)

def apimethod():
     temp = [self.get_data(i) for i in self.collection.find()]
     return jsonify(temp)

also dumps from pymongo don’t help alot

from bson.json_util import dumps,loads

because it is returning a string instead of dict which was expected in my situation to create API and I have to load again if I did dumps.

This thread helped me – thank you.

Wanted to share my final solution to get the JSON back into a JSON/Dictionary Object: (Based on your example)

from bson.json_util import dumps, loads
r = collection.find()
l = list(r) # Converts object to list
d = dumps(l) # Converts to String
dict_needed = loads(d[0]) # Serializes String and creates dictionary

Now you have the JSON in a dictionary object and can edit as needed.

I was facing the same issue, I wrote a code that converts document to dictionary. You can use that for reference. Pass the object obtained by find_one() into documentToJson() method and the results of find() into convertDocumentsToJson. There is type in the name Json, instead the code converts to Dict rather than json.

from bson.json_util import dumps

class UtilService:

def __init__(self):

def pinCodeParser(path):
    location = {}
    f = open(path)
    for line in f:
        words = line.split()
        location[words[1]] = (words[-3],words[-2])
    return location

def listHelper(str):
    s = []
    str = str.split(',')
    for e in str:
    return s

def parseList(str):
    if ',' in str:
        return UtilService.listHelper(str)
    return str

def trimStr(str):
    return str.replace('"','')

def documentToJson(document):
    document = eval(dumps(document))
    mp = {}
    for key, value in document.iteritems():
        if "_id" in key:
            mp["id"] = str(value["$oid"])
            mp[ UtilService.trimStr(key) ] = UtilService.parseList( value )
    return mp

def convertDocumentsToJson(documents):
    result = []
    for document in documents:
    return result