This script bans SMG from the server by making it unselectable, and forwarding the player to the rifle. This is the script we've all been waiting for.
Tested with the 0.76 branch of pyspades, on a local network with 2 players (me and me). Assumed to work on 0.75, but not confirmed.
Download it from Gist: smgsucks.py (click the Download button on the page, or the "raw" link if you prefer)