TicTacToe - SOS

This is maybe my first game I programmed using python. I have used the native python library "turtle" for the graphics, because I was a beginner back then and I did not know anything :).  The game is a combination of the classic tictactoe and the game sos, but you can give the grid any size you want (for example, instead of the usual 3x3 you can resize it to be 10x10, although I wouldn't recommend you to choose over 30x30, because the program runs very slowly then). The objective of the game is to score as many points as you can by creating triplets of your mark/color (horizontally, vertically or diagonally). There are 3 game modes: play against the computer, against another person (on the same computer), or let the computer play against itself.  The computer thinks two moves ahead to maximize its score and to prevent you from scoring too high. Do not underestimate it, it will probably win some games before you understand the way it thinks and eventually (?) you take the upper hand.