If Statement Error (Tic Tac Toe)

[ale.of.ginger at gmail.com]

Nevermind my previous reply: I've been fixing up the code and
understand it.  I'm at a nifty 80 lines where I am at now rather than
209 lines in the previous version!  The changes are immense!

The only problem I have is whenever player two goes, it says the cell
is filled.  But the code:

if gameboard[cell] not in 'OX':
                gameboard[cell] = 'X'
            else:
                print "This cell is already filled."
                turnnumber = turnnumber - 1

is not any different than the code I am using for player one.  Anything
I have to change regarding 'OX' or something else?