Python Pyramid not rendering JSON correctly -

i using mongoengine's to_json method on object wish render in json-rendered pyarmid page. i've done lots of json rendering in pyramid, not mongoengine. mongoengine's to_json method simple calls json_util.dumps. works fine in python. problem when pyramid renders page, rendered this:

{   "0": "\"",   "1": "{",   "2": "\\",   "3": "\"",   "4": "_",  etc... 

however, json dump looks ok in python, before rendered:

'{"_id": {"$oid": "4ebca43ccc7a67085b000000"}, "created": {"$date": 1346419407715}, "modified": {"$date": 1403757381829}, "modified_by": {"$oid": "4ebca43ccc7a67085b000000"}, "email":  etc... 

as has been suggested in comments, seems json being jsonified more once, can't figure out where.

i pick user object database , attach every request:

def get_user(request):     return user.objects(id=objectid(authenticated_userid(request))).first()  config.add_request_method(get_user, 'user', reify=true) 

i return user per request:

@view_config(route_name='api.user', permission='authenticated', renderer='json') def user_vc(request):     response = request.response     _id = request.matchdict['id']     if _id == 'session':         user = request.user         if not user:             response.status = 403             return response         else:             print user  # user object expected (not json)             return user 

i have custom adapter handle user object:

# custom json adapters custom_json = json()  def user_adapter(obj, request):     print obj.to_json()  # json looks ok here     return obj.to_json() custom_json.add_adapter(user, user_adapter)  config.add_renderer('json', custom_json) 

i not doing other jsonification myself, apart adapter above. is?? great.

thanks comment @anttihappala above, found problem. mongoengine's to_json method converts objects jsonified string. however, pyramid needs json data structure. so, fix it, added following function custom renderer:

def render_to_json(obj):         return json.loads(obj.to_json())      def user_adapter(obj, request):         return render_to_json(obj)     custom_json.add_adapter(user, user_adapter) 

i can add custom renderer other mongoengine objects , return them natively.