If ever you use nginx, which is a good choice :), you may use the push module http://pushmodule.slact.net/, I found it rather easy to use.
You have one URL to publish messages on a channel (that can be done easily in python, with httplib for example), and one URL to pull messages from a channel (and a channel may be used by more than one user). See also http://blog.jamieisaacs.com/2010/08/27/comet-with-nginx-and-jquery/ for a jquery integration.
