def read_user_documents_generator(user_twitter_id_list, client, mongo_database_name, mongo_collection_name):
    """
    Stores Twitter list objects that a Twitter user is a member of in different mongo collections.

    Inputs: - user_twitter_id_list: A python list of Twitter user ids.
            - client: A pymongo MongoClient object.
            - mongo_database_name: The name of a Mongo database as a string.
            - mongo_collection_name: The name of the mongo collection as a string.

    Yields: - user_twitter_id: A Twitter user id.
            - twitter_list_gen: A python generator that yields Twitter lists in dictionary (json) format.
    """
    mongo_database = client[mongo_database_name]
    mongo_collection = mongo_database[mongo_collection_name]

    # cursor = mongo_collection.find({"_id": {"$in": [int(user_twitter_id) for user_twitter_id in user_twitter_id_list]}})
    cursor = mongo_collection.find()

    user_twitter_id_list = [int(user_twitter_id) for user_twitter_id in user_twitter_id_list]
    user_twitter_id_list = set(user_twitter_id_list)

    for documents in cursor:
        if documents["_id"] in user_twitter_id_list:
            yield documents["_id"], documents