code: def from_board(cls, board):
          '''
          :param Board board: board to represent
          :return: SkinnyBoard to represent the given Board
          '''
          if len(board):
              left = board.left_end()
              right = board.right_end()
          else:
              left = None
              right = None
  
          return cls(left, right, len(board)f from_board(cls, board):
          '''
          :param Board board: board to represent
          :return: SkinnyBoard to represent the given Board
          '''
          if len(board):
              left = board.left_end()
              right = board.right_end()
          else:
              left = None
              right = None
  
          return cls(left, right, len(board))
docs: :param Board board: board to represent
          :return: SkinnyBoard to represent the given Board