read pgn move in san

[sugizo]

code

class JupyterChessPGN:
    out_position = None # widgets.Output(layout = {'border': '1px solid red'})

    def __init__(self, pgnfile):
        self.pgnfile = pgnfile
        
    def make_games_info(self, pgnfile):
        games_info = [] 
        pgn = open(self.pgnfile)
        game_number = 1
        while True:
            game = chess.pgn.read_game(pgn)
            if game is None:
                break
            else:
                white = game.headers.get("White")
                black = game.headers.get("Black")
                result = game.headers.get("Result")
                info = white + " - " + black + " " + result + " (g " + str(game_number) + ")", game_number - 1
                games_info.append((info) )
                game_number = game_number + 1
        return games_info
    
    def on_change_game(self, change):
        game_no = change['new']
        print("Game No :", game_no)
        self.set_ith_game(int(game_no) )
        self.showUI()
        
    def make_game_list(self):
        self.widget_games = widgets.Dropdown(
            options = self.make_games_info(self.pgnfile),
            description = 'Game :',
            disabled = False
        )
        self.widget_games.observe(self.on_change_game, names = 'value')
        return self.widget_games

    def read_ith_game(self, i):
        pgn = open(self.pgnfile)
        game_number = 0
        while game_number <= i:
            ga = chess.pgn.read_game(pgn)
            if ga is None:
                return None
            else:
                if (game_number == i):
                    return ga
            game_number = game_number + 1
        return None
    
    def set_ith_game(self, i):
        self.game = self.read_ith_game(i)
        return self.game

    def display_html(self, board):
        if board.turn == chess.WHITE:
            turn_color = 'White'
        else:
            turn_color = 'Black'
        ply = board.ply()
        fen = board.fen()
        epd = board.epd()
        move_stack = board.move_stack
        if ply == 0:
            uci = ''
            san = ''
            variation_san = ''
        else:
            uci = move_stack[ply - 1]
            #san = board.san(uci)
            san = board.root().san(uci)
            variation_san = board.root().variation_san(move_stack)
        
        html = """
        <table>
        <tr>
        <th rowspan = "7" style = "width:45%%;text-align: center">%s</th>
        <th style = "text-align: left">Board</th>
        <td style = "text-align: left"><pre>%s</pre></td>
        </tr>
        <tr>
        <th style = "text-align: left">Turn</th>
        <td style = "text-align: left">%s</td>
        </tr>
        <tr>
        <th style = "text-align: left">Ply</th>
        <td style = "text-align: left">%s</td>
        </tr>
        <tr>
        <th style = "text-align: left">Move</th>
        <td style = "text-align: left">UCI : %s<br />SAN : %s</td>
        </tr>
        <tr>
        <th style = "text-align: left">FEN</th>
        <td style = "text-align: left">%s</td>
        </tr>
        <tr>
        <th style = "text-align: left">EPD</th>
        <td style = "text-align: left">%s</td>
        </tr>
        <tr>
        <th style = "text-align: left">Variation SAN</th>
        <td style = "text-align: left">%s</td>
        </tr>
        </table>
        """ % (board._repr_svg_(), board, turn_color, 
               ply, uci, san, fen, epd, variation_san)

        return html
        
    def previous_button(self, b):
        if (self.nm is not 0):
            self.nm = self.nm - 1
            self.board.pop()
            
        with self.out_position:
            clear_output(wait = True) 
            display(HTML(self.display_html(self.board) ) )

    def next_button(self, b):
        if (self.nm < len(self.moves) ):
            m = self.moves[self.nm]
            self.board.push(m)
            
            with self.out_position:
                clear_output(wait = True) 
                display(HTML(self.display_html(self.board) ) )
            self.nm = self.nm + 1

    def showUI(self):
        clear_output()
        self.board = chess.Board()
        self.moves = list(self.game.mainline_moves() )
        self.nm = 0
        
        if (self.out_position is not None):
            self.out_position.clear_output()
        display(self.widget_games)
        
        self.out_position = widgets.Output() # layout = {'border': 'px solid red'})
        display(self.out_position)
        with self.out_position:
            display(HTML(self.display_html(self.board) ) )
            
        self.out = widgets.Output()
        with self.out:
            clear_output()
            self.previous_b = widgets.Button(description = "Previous")
            self.next_b = widgets.Button(description = "Next")

            self.previous_b.on_click(self.previous_button)
            self.next_b.on_click(self.next_button)

            display(HBox([self.previous_b, self.next_b] ) )

        display(self.out)
        
pgnfile = "pgn/chess-pgn.pgn"
jc = JupyterChessPGN(pgnfile)

jc.make_game_list()
jc.set_ith_game(0)
jc.showUI()

above code
san = board.san(uci)

result
AssertionError: san() and lan() expect move to be legal or null, but got g1h3 in rnbqkbnr/pppppppp/8/8/8/7N/PPPPPPPP/RNBQKB1R b KQkq - 1 1

on the first try ipywidget next button

and
san = board.root().san(uci)

result on the third ply (means it works on the ply 1 and 2 but an error occured on ply 3)
AssertionError: san() and lan() expect move to be legal or null, but got h3g5 in rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1

environment
jupyter notebook

question
how to read pgn move in san ?