Solver for 'ghost' word game

ghost.py

words = set()

with open( "sowpods.txt", "r" ) as wordFile:
    for x in wordFile:
        words.add( x.rstrip() )

maxLen = max( len(x) for x in words )

alphabet = [ 'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I',
             'J', 'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R',
             'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z' ]

_infixes = [ set() for i in xrange( maxLen + 1 ) ]
_infixesBuilt = False

def build_infixes():
    for w in words:
        for l in xrange( 2, len( w ) ):
            for i in xrange( 0, l ):
                 _infixes[l].add( w[i:i+l] )
    global _infixesBuilt
    _infixesBuilt = True
    
winners = {}

def winner( position ):
    if not _infixesBuilt:
        build_infixes()

    # Previous player said a word, current player wins
    if len( position ) >= 4 and position in words:
        #print position, "word", "N"
        return "N"
    # No words available, current player challenges and wins
    if len( position ) >= 2 and position not in _infixes[ len( position ) ]:
        #print position, "noprefix", "N"
        return "N"
    
    if position in winners:
        #print position, "already winner", "N"
        return "N"
            
    for a in alphabet:
        for np in [ position + a, a + position ]:
            if winner( np ) == "P":
                winners[ position ] = np
                #print position, "move to", np, "N"
                return "N"

    # Previous player wins only if next player has no winning move
    #print position, "no good move", "P"
    return "P"

def winningMove( position ):
    # Doesn't return good results if this was not a part of the
    # tree that was explored.
    
    if position in winners:
        print "move to", winners[position]
        return
            
    if len( position ) >=2 and position not in _infixes[ len( position ) ]:
        print "challenge"
        return

    if len( position ) >=4 and position in words:
        print "losing position, valid word"
        return
    
    print "losing position"
    losingWords = []
    challengeMoves = []
    for a in alphabet:
        for (w,short) in [ ( position + a, "*" + a ), ( a + position, a + "*" ) ]:
            if len( w ) >= 4 and w in words:
                losingWords.append( w )
            elif w in winners:
                print w, "response is", winners[w]
            elif len ( w ) >= 2 and w not in _infixes[ len( w ) ]:
                challengeMoves.append( short )
        
    print "Valid words:", " ".join( losingWords )
    print "Challenge positions:", " ".join( challengeMoves )