ref: d05dbeb9a44c298a01e741c1bffb68591b87b5f5
dir: /sys/src/cmd/python/Doc/lib/sqlite3/md5func.py/
import sqlite3
import md5
def md5sum(t):
    return md5.md5(t).hexdigest()
con = sqlite3.connect(":memory:")
con.create_function("md5", 1, md5sum)
cur = con.cursor()
cur.execute("select md5(?)", ("foo",))
print cur.fetchone()[0]