First solution in Clear category for Xs and Os Referee by
l = [list(x) for x in b] + [[x[i] for x in b] for i in range(len(b))]
l += [[x[i] for i,x in enumerate(b)],[x[-i-1] for i,x in enumerate(b)]]
if list("XXX") in l: return "X"
if list("OOO") in l: return "O"
May 1, 2014