Is a single Python executable file shared by all clients when run on a server?
With Tornado you'll have at least one process per machine/VM (Heroku calls these "dynos"); in multicore environments you'll want to run multiple processes per machine (one per core).  Each process handles many users, so in the simple case where there is only one process you can use global variables to share state between users, although as you grow to multiple dynos and processes you'll need some sort of inter-process communication.
I've been working with a Tornado project on my local machine by running server.py. When deployed to the server (e.g. Heroku), will a single instance of server.py be shared by all clients or will each client have their own running version? I am wondering this because I am thinking of making use of global variables in server.py and wondering if they will be shared across all clients or just a single client.