Python shelve vs. sqlite3

I have a huge Python dict that I can't store in the memory. Python provides a shelve module for this purpose. It acts like a regular dict but it can be saved into a file. I wonder its performance comparing to sqlite3, so I run this little test:

import shelve
import sqlite3

def test_sqlite3():
    conn = sqlite3.connect("debug.s3db")
    cur = conn.cursor()
    cur.execute("CREATE TABLE IF NOT EXISTS [mydict] ("
                "[key] VARCHAR(255) PRIMARY KEY NOT NULL, "
                "[value] VARCHAR(255) NOT NULL)")
    for i in xrange(0, 1000000):
        cur.execute("INSERT INTO [mydict] (key, value) VALUES (?, ?)",
                    (str(i), str(i*2)))
    conn.commit()
    cur.close()
    conn.close()
    
def test_shelve():
    d = shelve.open("debug.shelf")
    for i in xrange(0, 1000000):
        d[str(i)] = str(i*2)
    d.close()

On my computer, test_sqlite3() cost me about 25 seconds, and about 51 seconds for test_shelve(). I also performed some fetch queries on these two, sqlite3 still runs faster than shelve. In conclusion, sqlite3 wins!