Algorithm for swtiching instruments in rockband. http://blog.paulisageek.com/2009/10/rock-band-group-algorithm.html

rockband.py

import random
import sys

instruments = ["Drums", "Vocals", "Guitar", "Bass"]

people = sys.argv[1:]
if len(people) == 0:
    print "python rockband.py Name1 Name2 ..."
    sys.exit()
if len(people) < len(instruments):
    print "If there is less than %d people, just pick some instruments, rotate, and then shuffle. You don't need me for that" % len(instruments)
    sys.exit()

random.shuffle(people)
num = len(people)

places = [' Gap']*num
instruments_ids = [0, int(num*0.25), int(num*0.5), int(num*0.75)]
for i, ins in zip(instruments_ids, instruments):
    places[i] = ins

while True :
    for l,n in zip(places, people):
        print "%s:\t%s" % (l, n)

    if raw_input("Press <Enter> once you finished a round: ") == "q" :
        break

    print ""
    playing = [people[x] for x in instruments_ids]
    not_playing = list(set(people) - set(playing))

    if len(not_playing) < len(instruments) :
        new_playing = not_playing + random.sample(playing, len(instruments) - len(not_playing))
    else :
        new_playing = random.sample(not_playing, len(instruments))

    new_not_playing = list(set(people) - set(new_playing))
    random.shuffle(new_playing)
    random.shuffle(new_not_playing)

    people = [None]*num
    for i, p in zip(instruments_ids, new_playing) :
        people[i] = p

    count = 0
    for i in xrange(len(people)) :
        if not people[i] :
            people[i] = new_not_playing[count]
            count += 1