我需要使用pymongo用python搜索ObjectId，但是我总是会收到此错误。有什么想法如何搜索？

import pymongo
from pymongo import MongoClient
from pymongo import ObjectId

gate = collection.find({'_id': ObjectId(modem["dis_imei"])})
print gate

    Traceback (most recent call last):
  File "C:\Users\gerswin\Documents\Proyectos\Demonio py\test.py", line 2, in <module>
    import pymongo
  File "C:\Python27\lib\site-packages\pymongo\__init__.py", line 80, in <module>
    from pymongo.connection import Connection
  File "C:\Python27\lib\site-packages\pymongo\connection.py", line 39, in <module>
    from pymongo.mongo_client import MongoClient
  File "C:\Python27\lib\site-packages\pymongo\mongo_client.py", line 45, in <module>
    from pymongo import (auth,
  File "C:\Python27\lib\site-packages\pymongo\database.py", line 22, in <module>
    from pymongo.collection import Collection
  File "C:\Python27\lib\site-packages\pymongo\collection.py", line 25, in <module>
    from pymongo.cursor import Cursor
  File "C:\Python27\lib\site-packages\pymongo\cursor.py", line 19, in <module>
    from bson import RE_TYPE
ImportError: cannot import name RE_TYPE