gistfile1.py

def update_elo_score(k=32, defender_rating=1000, attacker_rating=1000, attacker_won=False):
    q_a = 10**(defender_rating/400.0)
    q_b = 10**(attacker_rating/400.0)
    expected_defender_score = q_a / float(q_a + q_b)
    expected_attacker_score = q_b / float(q_b + q_a)
    print "Expected chance of winning, defender %0.1f%%, attacker %0.1f%%" % (expected_defender_score*100, expected_attacker_score*100)
    if attacker_won:
        updated_defender_rating = defender_rating + int(k * (0 - expected_defender_score))
        updated_attacker_rating = attacker_rating + int(k * (1 - expected_attacker_score))
    else:
        updated_defender_rating = defender_rating + int(k * (1 - expected_defender_score))
        updated_attacker_rating = attacker_rating + int(k * (0 - expected_attacker_score))
    return updated_defender_rating, updated_attacker_rating