Extract Lichess game URLs from a PGN download for games where Black played the Pirc Defence

pgn_find_pirc_defence.py

#! /usr/bin/env python3
# Copyright (C) 2021 Sebastian Pipping <sebastian@pipping.org>
# Licensed under the Apache 2.0 License
# Version 2021-08-19 00:51 UTC+2

import argparse
from typing import List

import chess
import chess.pgn  # https://python-chess.readthedocs.io/en/latest/pgn.html


def is_turn(board, for_white: bool) -> bool:
    return board.turn == for_white


def matches_opening(opening_moves: List[str], game_moves: List[chess.Move], for_white: bool) -> bool:
    for i, expected_uci in enumerate(opening_moves):
        move_index = 2 * i + int(not for_white)
        try:
            if game_moves[move_index] != chess.Move.from_uci(expected_uci):
                return False
        except IndexError:
            return False
    return True


if __name__ == '__main__':
    parser = argparse.ArgumentParser()
    parser.add_argument('pgn_file', metavar='PGN_FILE')
    config = parser.parse_args()

    default_board = chess.Board()

    moves_pirc_defence = [
        'd7d6',
        'g8f6',
        'g7g6',
    ]

    with open(config.pgn_file) as f:
        while True:
            game = chess.pgn.read_game(f)
            if game is None:
                break

            url = game.headers['Site']

            board = game.board()
            if board != default_board or not is_turn(board, for_white=True):
                continue

            moves = list(game.mainline_moves())

            if matches_opening(moves_pirc_defence, moves, for_white=False):
                print(f'{url}/black#6')