import sqlite3

def collate_reverse(string1, string2):

    return -cmp(string1, string2)

con = sqlite3.connect(":memory:")

con.create_collation("reverse", collate_reverse)

cur = con.cursor()

cur.execute("create table test(x)")

cur.executemany("insert into test(x) values (?)", [("a",), ("b",)])

cur.execute("select x from test order by x collate reverse")

for row in cur:

    print row

con.close()