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"""
Custom Chess Tokenizer - Decomposed Move Representation.
Decomposes chess moves into components: Color, Piece, From square, To square, Modifiers.
Uses a fixed vocabulary of ~88 tokens.
"""
from __future__ import annotations
import json
import os
import re
from typing import Dict, List, Optional
from transformers import PreTrainedTokenizer
class ChessTokenizer(PreTrainedTokenizer):
model_input_names = ["input_ids", "attention_mask"]
PAD_TOKEN = "[PAD]"
BOS_TOKEN = "[BOS]"
EOS_TOKEN = "[EOS]"
UNK_TOKEN = "[UNK]"
COLORS = ["[W]", "[B]"]
PIECES = ["P", "N", "B", "R", "Q", "K"]
SQUARES = [f + r for f in "abcdefgh" for r in "12345678"]
MODIFIERS = ["x", "+", "#", "+*", "=Q", "=R", "=B", "=N", "O-O", "O-O-O", "o", "O"]
MOVE_PATTERN = re.compile(
r'^([WB])([PNBRQK])([a-h][1-8])([a-h][1-8])(=[QRBN])?(\([xoO+*]+\))?$'
)
def __init__(
self,
vocab_file: Optional[str] = None,
vocab: Optional[Dict[str, int]] = None,
**kwargs,
):
self._pad_token = self.PAD_TOKEN
self._bos_token = self.BOS_TOKEN
self._eos_token = self.EOS_TOKEN
self._unk_token = self.UNK_TOKEN
kwargs.pop("pad_token", None)
kwargs.pop("bos_token", None)
kwargs.pop("eos_token", None)
kwargs.pop("unk_token", None)
if vocab is not None:
self._vocab = vocab
elif vocab_file is not None and os.path.exists(vocab_file):
with open(vocab_file, "r", encoding="utf-8") as f:
self._vocab = json.load(f)
else:
self._vocab = self._create_default_vocab()
self._ids_to_tokens = {v: k for k, v in self._vocab.items()}
super().__init__(
pad_token=self._pad_token,
bos_token=self._bos_token,
eos_token=self._eos_token,
unk_token=self._unk_token,
**kwargs,
)
def _create_default_vocab(self) -> Dict[str, int]:
tokens = [self.PAD_TOKEN, self.BOS_TOKEN, self.EOS_TOKEN, self.UNK_TOKEN]
tokens.extend(self.COLORS)
tokens.extend(self.PIECES)
tokens.extend(self.SQUARES)
tokens.extend(self.MODIFIERS)
return {token: idx for idx, token in enumerate(tokens)}
def _parse_move(self, move: str) -> List[str]:
"""Parse a single move into component tokens."""
match = self.MOVE_PATTERN.match(move)
if not match:
return [self.UNK_TOKEN]
tokens = [f"[{match.group(1)}]", match.group(2), match.group(3), match.group(4)]
if match.group(5):
tokens.append(match.group(5))
if match.group(6):
suffix_content = match.group(6)[1:-1]
if "x" in suffix_content:
tokens.append("x")
if "+*" in suffix_content:
tokens.append("+*")
elif "+" in suffix_content:
tokens.append("+")
if suffix_content == "o":
tokens.append("o")
elif suffix_content == "O":
tokens.append("O")
return tokens
def _tokenize(self, text: str) -> List[str]:
"""Tokenize a string of moves into component tokens."""
tokens = []
for move in text.strip().split():
tokens.extend(self._parse_move(move))
return tokens
def _convert_token_to_id(self, token: str) -> int:
return self._vocab.get(token, self._vocab.get(self.UNK_TOKEN, 0))
def _convert_id_to_token(self, index: int) -> str:
return self._ids_to_tokens.get(index, self.UNK_TOKEN)
def convert_tokens_to_string(self, tokens: List[str]) -> str:
"""Reconstruct moves from component tokens."""
special = {self.PAD_TOKEN, self.BOS_TOKEN, self.EOS_TOKEN, self.UNK_TOKEN}
result = []
current_move = []
for token in tokens:
if token in special:
if current_move:
result.append(self._reconstruct_move(current_move))
current_move = []
continue
current_move.append(token)
if self._is_complete_move(current_move):
result.append(self._reconstruct_move(current_move))
current_move = []
if current_move:
result.append(self._reconstruct_move(current_move))
return " ".join(result)
def _is_complete_move(self, tokens: List[str]) -> bool:
"""Check if tokens form a complete move."""
if len(tokens) < 4:
return False
if (tokens[0] in self.COLORS and tokens[1] in self.PIECES and
tokens[2] in self.SQUARES and tokens[3] in self.SQUARES):
if len(tokens) == 4:
return True
for t in tokens[4:]:
if t in self.COLORS or (t not in self.MODIFIERS and not t.startswith("=")):
return True
return True
return False
def _reconstruct_move(self, tokens: List[str]) -> str:
"""Reconstruct a move string from component tokens."""
if not tokens or len(tokens) < 4:
return "".join(tokens)
color = tokens[0][1] if tokens[0] in self.COLORS else tokens[0]
move = color + "".join(tokens[1:4])
suffixes = []
for t in tokens[4:]:
if t.startswith("="):
move += t
elif t in ["x", "+", "+*", "o", "O"]:
suffixes.append(t)
if suffixes:
move += "(" + "".join(suffixes) + ")"
return move
def save_vocabulary(self, save_directory: str, filename_prefix: Optional[str] = None) -> tuple:
if not os.path.isdir(save_directory):
os.makedirs(save_directory, exist_ok=True)
vocab_file = os.path.join(
save_directory, (filename_prefix + "-" if filename_prefix else "") + "vocab.json"
)
with open(vocab_file, "w", encoding="utf-8") as f:
json.dump(self._vocab, f, ensure_ascii=False, indent=2)
return (vocab_file,)
@classmethod
def build_vocab_from_iterator(cls, iterator, min_frequency=1):
return cls()
@classmethod
def build_vocab_from_dataset(cls, **kwargs):
return cls()
@property
def vocab_size(self) -> int:
return len(self._vocab)
def get_vocab(self) -> Dict[str, int]:
return dict(self._vocab)
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