I am using pymongo driver. Supposedly, one can use a string to query the _id field of a document, like this:
thing = db.things.find_one({\'_id\':\'4ea113d6b6848
thing = db.things.find_one({'_id':ObjectId('4ea113d6b684853c8e000001')}) should work
thing = db.things.find_one({'_id':ObjectId('4ea113d6b684853c8e000001')})