从bson中导入ObjectId对象，将字符串转换成id对象查询使用：

from bson import ObjectId
import pymongo
conn = pymongo.MongoClient('mongodb://root:abc123@127.0.0.1/admin'
str = "5sdfadsfasdfxzcasdfasdfas"
findinfo = conn.db_name.table_name.find({"_id" : ObjectId(str)})