def get_diagonal(corner_square):
    """ Returns the diagonal that includes the given corner square.
    Only (1, A), (1, C), (3, A) and (3, C) are corner squares. """
    if corner_square == (1, A) or corner_square == (3, C):
        return [get_square((1, A)), get_square((2, B)), get_square((3, C))]
    else:
        return [get_square((1, C)), get_square((2, B)), get_square((3, A))]
 Returns the diagonal that includes the given corner square.
    Only (1, A), (1, C), (3, A) and (3, C) are corner squares. 
recipes/Python/576661_TicTacToe/recipe-576661.py