How to use cx_Oracle session pool with Flask gracefuly?

I'm a newbie to Python and Flask, and I use Oracle, when learning Flask tutorial, I code as follow, but it smells really bad, please help me with these questions, thanks a lot!

1) need I release connection to poll explicitly?

2) how can I implement poll acquire and release gracefully?

def get_dbpool():
if not hasattr(g, 'db_pool'):
    g.dbPool = connect_db()
return g.dbPool

@app.teardown_appcontext
def close_db(error):
    if hasattr(g, 'db_pool'):
        g.dbPool.close()

@app.route('/')
def hello_world():
    db = get_dbpool().acquire()
    cursor=db.cursor()
    sql=''
    cursor.execute(sql)
    rows = cursor.fetchall()
    cursor.close()
    get_dbpool().release(db)
    return json.jsonify(combines=rows)

Copyright Notice：Content Author:「taoeaten」，Reproduced under the CC 4.0 BY-SA copyright license with a link to the original source and this disclaimer.
Link to original article：https://stackoverflow.com/questions/48517547/how-to-use-cx-oracle-session-pool-with-flask-gracefuly