Number of visitors in Django
Edit: Added some more information about why I present this answer here.  I found chartbeat when I tried to answer this same question for my django based site.  I don't work for them.
Not specifically Django, but chartbeat.com is very interesting to add to a website as well.
django-tracking is great, +1 for that answer, etc.  
Couple of things I could not do with django-tracking, that chartbeat helped with; tracked interactions with completely cached pages which never hit the django tracking code and pages not delivered through django (e.g. wordpress, etc.)
In Django, how can I see the number of current visitors? Or how do I determine the number of active sessions?
Is this a good method?
use django.contrib.sessions.models.Session, set the expiry time short. Every time when somebody does something on the site, update expiry time. Then count the number of sessions that are not expired.