python - MongoDB query doesn't behave as expected with nested elements -

i'm trying return results match value , match on child properties. want return results match month , match range of values. find simple search, doesn't seem return results expect.

using pymongo query is:

month = 2 results = db.master.find({"months": str(month)}) 

this should surely return matching documents correct month. no records returns month=2

my data stored in mdb as:

{     "_id": {         "$oid": "568d0bebc1bed847da7a2e6f"     },     "months": {         "2": {             "std_rank": 0.11338862902393358,             "rank_gain": 0.6183933826187626,             "gain": 0.9618213660245183,             "std": 0.021891473641317716         },     "months": {         "3": {             "std_rank": 0.11338862902393358,             "rank_gain": 0.6183933826187626,             "gain": 0.9618213660245183,             "std": 0.021891473641317716         },        },     "code": "vu" } 

one suggested answer works filtering correct month, question how apply filter child elements. example:

results = db.master.find({}, {"_id": 0, "months." + str(month): 1, "months.std_rank": {"$lte": max_std_rank, "$gte": min_std_rank} } ) 

i following error:

pymongo.errors.operationfailure: database error: can't canonicalize query: badvalue >1 field in obj: { $gte: 0.0, $lte: 1.0 } 

try following query

results = db.master.find({ "months." + str(month) + ".std_rank": {"$lte": max_std_rank, "$gte": min_std_rank } }, { "_id": 0, "months." + str(month): 1 } ) 

which uses projection return document matching given month key.