Can't get values from sqlite database

[Blindingend]

my code is like:

import records
db = records.Database("sqlite:///test_db.db")
rows = db.query("select * from test_table")
print(rows[0])

I'm pretty sure there is content in test table and other operations like 'insert' or create_table is perfectly normal. But when I use select query like README, it throws an exception as I'm fetching the data from row, says Cannot operate on a closed database.