import sqlite3 class MySum:    def __init__(self):        self.count = 0     def step(self, value):        self.count += value     def finalize(self):        return self.count con = sqlite3.connect(":memory:")con.create_aggregate("mysum", 1, MySum)cur = con.cursor()cur.execute("create table test(i)")cur.execute("insert into test(i) values (1)")cur.execute("insert into test(i) values (2)")cur.execute("select mysum(i) from test")print cur.fetchone()[0]