elo.py [xonotic/xonstats]

#!/usr/bin/env/python
#-*- coding: utf8 -*-

import sys

def delta(S, E, K=40):
    return K * (S - E)

def E(Qa, Qb):
    return float(Qa)/(Qa+Qb)

def Q(elo):
    return 10**(elo/400)

if __name__ == "__main__":
    eloa, elob, Ka, Kb = None, None, 40, 40
    if len(sys.argv) > 1:
        eloa = float(sys.argv[1])
    if len(sys.argv) > 2:
        elob = float(sys.argv[2])
    if len(sys.argv) > 3:
        Ka = float(sys.argv[3])
    if len(sys.argv) > 4:
        Kb = float(sys.argv[4])

    if  not eloa or not elob:
        print "Usage:", sys.argv[0], "<eloA> <eloB> [kA] [kB]"
        print "Calculate elo win/loss of a match between two players"
        print "\teloA, eloB: \tcurrent elo scores (new players start with 100)"
        print "\tkA, kB: \tcurrent K-factors (40 by default; new players start with 200)"
        sys.exit(1)

    Qa, Qb = Q(eloa), Q(elob)
    Ea, Eb = E(Qa, Qb), E(Qb, Qa)

    print "A has elo %8.3f at K = %3d" % (eloa, Ka)
    print "B has elo %8.3f at K = %3d" % (elob, Kb)

    print

    print "Outcome 1: A wins"
    print "\tA gains %7.3f points" %  delta(1, Ea, Ka)
    print "\tB loses %7.3f points" % -delta(0, Eb, Kb)

    print

    print "Outcome 2: B wins"
    print "\tA gains %7.3f points" % -delta(0, Ea, Ka)
    print "\tB loses %7.3f points" %  delta(1, Eb, Kb)