python - BadYieldError when using find() Motor [MongoDB + Tornado] -

i new python tornado framework. have small collection of data in mongodb. using simple function in python file. badyielderror when using db.collection.find() option. db.collection.find_one() works fine display 1 record.

import tornado import bson bson import json_util bson.json_util import dumps class typelist(apihandler): @gen.coroutine def get(self):     doc = yield db.vtype.find()     self.write(json_util.dumps(doc)) 

the error is:

tornado.gen.badyielderror: yielded unknown object motorcursor()

find returns motorcursor. yield cursor's fetch_next property advance cursor , call next_object() retrieve current document:

@gen.coroutine def do_find():     cursor = db.test_collection.find({'i': {'$lt': 5}})     while (yield cursor.fetch_next):         document = cursor.next_object()         print document 

please refer tutorial section querying more 1 document instructions on using motor's find , motorcursor.