Python: compact-ish unique identifiers

uniqid.py

import base64
import struct
from uuid import getnode as get_mac
import os
from threading import Lock
import time
from ssl import RAND_bytes as random_bytes

mac = struct.pack('>Q', get_mac())[2:] # do this now in case it is slow (see Python manual)

count = 0
count_lock = Lock()

def generate():
    global count
    our_count = 0
    with count_lock:
        count += 1
        our_count = count
    return base64.urlsafe_b64encode(mac + struct.pack('>dLH', time.time(), os.getpid(), (our_count % (2 ** 16))) + random_bytes(4))

updated 2014-01: change the order of the components which are output so as to result in less fragmentation when the IDs are used as keys in a B-Tree like data structure