Function isValidMove

src/gamesbyexample/reversegam.py:87–135

Returns False if the player's move on xstart, ystart is invalid. If it is a valid move, returns a list of spaces that would become the player's if they made a move here.

(board, tile, xstart, ystart)

def isValidMove(board, tile, xstart, ystart):
    """Returns False if the player's move on xstart, ystart is invalid.
    If it is a valid move, returns a list of spaces that would become
    the player's if they made a move here."""
    if board[(xstart, ystart)] != ' ' or not isOnBoard(xstart, ystart):
        return False

    board[(xstart, ystart)] = tile  # Set the tile on the board.

    if tile == 'X':
        otherTile = 'O'
    else:
        otherTile = 'X'

    tilesToFlip = []
    for xdirection, ydirection in ALL_DIRECTIONS:
        x, y = xstart, ystart
        x += xdirection  # First step in the x direction.
        y += ydirection  # First step in the y direction.
        if isOnBoard(x, y) and board[(x, y)] == otherTile:
            # Find if the other player's tile next to our tile.
            x += xdirection
            y += ydirection
            if not isOnBoard(x, y):
                continue
            while board[(x, y)] == otherTile:
                x += xdirection
                y += ydirection
                # Break out of while loop, then continue in for loop:
                if not isOnBoard(x, y):
                    break
            if not isOnBoard(x, y):
                continue
            if board[(x, y)] == tile:
                # Found tiles to flip over. Go in reverse direction
                # until we reach the original space, noting all the
                # tiles along the way.
                while True:
                    x -= xdirection
                    y -= ydirection
                    if x == xstart and y == ystart:
                        break
                    tilesToFlip.append([x, y])

    board[(xstart, ystart)] = ' '  # Restore the original empty space.
    # If no tiles were flipped, this is not a valid move:
    if len(tilesToFlip) == 0:
        return False
    return tilesToFlip


def isOnBoard(x, y):