Keep track of which users are currently online in your Python app using Redis

users_online.py

# 
# Demo script showing how to track which users are currently
# online and what URL they're looking at using py-Redis and
# ZSETs.
#
# Record that a user is online with
# mark_user_id_active(5, url="http://foo.com/my/url/woot")
#
# And get a list of which users are online, and what URL they're
# looking at with get_active_user_urls().
#
# Obviously, you'll need to change your Redis settings ...blah blah.
# License: BSD 3-clause.
#

import redis
import time
import itertools

# Track online users for 60s
#
TIMEOUT = 60

# Keep track of when we should remove old keys from our set of
# active users.  We do this once every ten times, just to save
# Redis memory.
#
time_to_purge = itertools.cycle([False] * 9 + [True])

def mark_user_id_active(user_id, url=None):
    """ Mark a user as "active".  This means adding the user id
        to the 'active-users' ZSET and, if a `url` is specified,
        adding a separate expiring key w/ that info.
    """
    redis_conn = redis.StrictRedis()
    pipe = redis_conn.pipeline()

    if url:
        # Store the URL this user is currently looking at for 60s
        pipe.setex("url-for-{0}".format(user_id), TIMEOUT, url)

    if time_to_purge.next():
        pipe.zremrangebyscore('active-users', 0, inttime(-TIMEOUT))

    # Store this user in our list of active users
    pipe.zadd('active-users', inttime(), user_id)
    pipe.execute()


def get_active_user_ids():
    """ Get a list of all users that are active
    """
    time_end = inttime()
    time_start = time_end - TIMEOUT
    return redis_conn.zrangebyscore('active-users', time_start, time_end)


def get_urls_for_user_ids(user_ids):
    """ Retreive the list of current URLs for a list of users that are active
    """
    redis_conn = redis.StrictRedis()
    urls = []
    if user_ids:
        urls = redis_conn.mget(
            ["url-for-{0}".format(user_id) for user_id in user_ids]
        )
    return urls

def get_active_user_urls():
    """ Retreive a list of user ids and the URLs that those users are 
        currently looking at...
    """
    active_user_ids = get_active_user_ids()
    urls = get_active_user_ids(active_user_ids)
    return zip(active_user_ids, urls)

FYI, this was copy/pasted from my project...not tested as a unit, but should work & at least shows the method.