Polyglot opening book reading

chess.polyglot.open_reader(path: PathLike) → MemoryMappedReader[source]

Creates a reader for the file at the given path.

The following example opens a book to find all entries for the start position:

>>> import chess
>>> import chess.polyglot
>>>
>>> board = chess.Board()
>>>
>>> with chess.polyglot.open_reader("data/polyglot/performance.bin") as reader:
...    for entry in reader.find_all(board):
...        print(entry.move, entry.weight, entry.learn)
e2e4 1 0
d2d4 1 0
c2c4 1 0
class chess.polyglot.Entry[source]

An entry from a Polyglot opening book.

key: int

The Zobrist hash of the position.

raw_move: int

The raw binary representation of the move. Use move instead.

weight: int

An integer value that can be used as the weight for this entry.

learn: int

Another integer value that can be used for extra information.

move: chess.Move

The Move.

class chess.polyglot.MemoryMappedReader(filename: PathLike)[source]

Maps a Polyglot opening book to memory.

find_all(board: Union[chess.Board, int], *, minimum_weight: int = 1, exclude_moves: Container[chess.Move] = []) → Iterator[Entry][source]

Seeks a specific position and yields corresponding entries.

find(board: Union[chess.Board, int], *, minimum_weight: int = 1, exclude_moves: Container[chess.Move] = []) → Entry[source]

Finds the main entry for the given position or Zobrist hash.

The main entry is the (first) entry with the highest weight.

By default, entries with weight 0 are excluded. This is a common way to delete entries from an opening book without compacting it. Pass minimum_weight 0 to select all entries.

Raises

IndexError if no entries are found. Use get() if you prefer to get None instead of an exception.

choice(board: Union[chess.Board, int], *, minimum_weight: int = 1, exclude_moves: Container[chess.Move] = [], random=<module 'random' from '/home/docs/checkouts/readthedocs.org/user_builds/python-chess/envs/latest/lib/python3.8/random.py'>) → Entry[source]

Uniformly selects a random entry for the given position.

Raises

IndexError if no entries are found.

weighted_choice(board: Union[chess.Board, int], *, exclude_moves: Container[chess.Move] = [], random=<module 'random' from '/home/docs/checkouts/readthedocs.org/user_builds/python-chess/envs/latest/lib/python3.8/random.py'>) → Entry[source]

Selects a random entry for the given position, distributed by the weights of the entries.

Raises

IndexError if no entries are found.

close() → None[source]

Closes the reader.

chess.polyglot.POLYGLOT_RANDOM_ARRAY = [0x9D39247E33776D41, ..., 0xF8D626AAAF278509]

Array of 781 polyglot compatible pseudo random values for Zobrist hashing.

chess.polyglot.zobrist_hash(board: chess.Board, *, _hasher: Callable[[chess.Board], int] = <chess.polyglot.ZobristHasher object>) → int[source]

Calculates the Polyglot Zobrist hash of the position.

A Zobrist hash is an XOR of pseudo-random values picked from an array. Which values are picked is decided by features of the position, such as piece positions, castling rights and en passant squares.