from random import Random

def play(change):
    """Play game
    @param change: True if player change after announce
    @return: True if player win"""

    choices = [1, 2, 3] # 1 is good, 2 and 3 are bad

    r = Random()

    #player choose : 
    player_choice = r.choice(choices)
    print "Player first choice: %s" % player_choice

    # We annouce one bad choice
    bad_choice = player_choice
    while bad_choice == player_choice:
        bad_choice = r.choice((2, 3))

    print "Bad choice announce: %s" % bad_choice

    if change:
        choices.remove(bad_choice)
        choices.remove(player_choice)
        player_choice = choices[0]
        print "player change choice to: %s" % player_choice

    if player_choice == 1:
        print "player win"
        return True
    else:
        print "player loose"
        return False

def main():
    n = 1000
    change_true = 0
    change_false = 0
    for i in range(n):
        r = play(True)
        if r:
            change_true += 1
    for i in range(n):
        r = play(False)
        if r:
            change_false += 1

    print "change_true win ratio: %s" % (100 * change_true / n)
    print "change_false win ratio: %s" % (100 * change_false / n)

if __name__ == "__main__":
    main()

Grr l’indentation du code est pourrie sur la preview… Que fait la police ?