parsing moves from pgn

Question

i have a service, that gets a game from database and adding moves to it. also, it edits current pgn (string of moves).Is there any functions, that can get given string of moves and parse moves from it?

I was trying this, but had a problem

board = chess.Board()
    if game.moves!="":
        for move in game.moves.split():
            board.push(chess.Move.from_uci(move))

And after trying to append first move to a new game i've got this issue:

board.push(chess.Move.from_uci(move))
           ^^^^^^^^^^^^^^^^^^^^^^^^^
raise InvalidMoveError(f"expected uci string to be of length 4 or 5: {uci!r}")
chess.InvalidMoveError: expected uci string to be of length 4 or 5: '1.'

Answer 1

Your game.moves has move numbers, like "1. e4", and likely does not have moves in UCI format either (which for example would be "e2e4").

To process PGN notation, use the chess.pgn library, and its read_game function.

Example:

import chess
import chess.pgn
import io

moves = "1. e4 e5 2. Nf3 *"
pgn = io.StringIO(moves)
game = chess.pgn.read_game(pgn)
board = game.board()
for move in game.mainline_moves():
    board.push(move)
    print(move)

This outputs:

e2e4
e7e5
g1f3

If in your attempt you had loaded game.moves from a file, then skip that, and load the pgn directly from that file with read_pgn:

pgn = open("yourfile.pgn")
game = chess.pgn.read_game(pgn)
# ...etc