Core

Colors

Constants for the side to move or the color of a piece.

chess.WHITE: chess.Color = True

chess.BLACK: chess.Color = False

You can get the opposite color using not color.

Piece types

chess.PAWN: chess.PieceType = 1

chess.KNIGHT: chess.PieceType = 2

chess.BISHOP: chess.PieceType = 3

chess.ROOK: chess.PieceType = 4

chess.QUEEN: chess.PieceType = 5

chess.KING: chess.PieceType = 6

chess.piece_symbol(piece_type: chess.PieceType) → str

chess.piece_name(piece_type: chess.PieceType) → str

Squares

chess.A1: chess.Square = 0

chess.B1: chess.Square = 1

and so on to

chess.G8: chess.Square = 62

chess.H8: chess.Square = 63

chess.SQUARES = [chess.A1, chess.B1, ..., chess.G8, chess.H8]

chess.SQUARE_NAMES = ['a1', 'b1', ..., 'g8', 'h8']

chess.FILE_NAMES = ['a', 'b', ..., 'g', 'h']

chess.RANK_NAMES = ['1', '2', ..., '7', '8']

chess.parse_square(name: str) → chess.Square

Gets the square index for the given square name (e.g., a1 returns 0).

Raises:

ValueError if the square name is invalid.

chess.square_name(square: chess.Square) → str

Gets the name of the square, like a3.

chess.square(file_index: int, rank_index: int) → chess.Square

Gets a square number by file and rank index.

chess.square_file(square: chess.Square) → int

Gets the file index of the square where 0 is the a-file.

chess.square_rank(square: chess.Square) → int

Gets the rank index of the square where 0 is the first rank.

chess.square_distance(a: chess.Square, b: chess.Square) → int

Gets the Chebyshev distance (i.e., the number of king steps) from square a to b.

chess.square_manhattan_distance(a: chess.Square, b: chess.Square) → int

Gets the Manhattan/Taxicab distance (i.e., the number of orthogonal king steps) from square a to b.

chess.square_knight_distance(a: chess.Square, b: chess.Square) → int

Gets the Knight distance (i.e., the number of knight moves) from square a to b.

chess.square_mirror(square: chess.Square) → chess.Square

Mirrors the square vertically.

Pieces

class chess.Piece(piece_type: chess.PieceType, color: chess.Color)

A piece with type and color.

piece_type: PieceType

The piece type.

color: Color

The piece color.

symbol() → str

Gets the symbol P, N, B, R, Q or K for white pieces or the lower-case variants for the black pieces.

unicode_symbol(*, invert_color: bool = False) → str

Gets the Unicode character for the piece.

classmethod from_symbol(symbol: str) → Piece

Creates a Piece instance from a piece symbol.

Raises:

ValueError if the symbol is invalid.

Moves

class chess.Move(from_square: chess.Square, to_square: chess.Square, promotion: chess.PieceType | None = None, drop: chess.PieceType | None = None)

Represents a move from a square to a square and possibly the promotion piece type.

Drops and null moves are supported.

from_square: Square

The source square.

to_square: Square

The target square.

promotion: PieceType | None = None

The promotion piece type or None.

drop: PieceType | None = None

The drop piece type or None.

uci() → str

Gets a UCI string for the move.

For example, a move from a7 to a8 would be a7a8 or a7a8q (if the latter is a promotion to a queen).

The UCI representation of a null move is 0000.

classmethod from_uci(uci: str) → Move

Parses a UCI string.

Raises:

InvalidMoveError if the UCI string is invalid.

classmethod null() → Move

Gets a null move.

A null move just passes the turn to the other side (and possibly forfeits en passant capturing). Null moves evaluate to False in boolean contexts.

>>> import chess
>>>
>>> bool(chess.Move.null())
False

Board

chess.STARTING_FEN = 'rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1'

The FEN for the standard chess starting position.

chess.STARTING_BOARD_FEN = 'rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR'

The board part of the FEN for the standard chess starting position.

class chess.Board(fen: str | None = 'rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1', *, chess960: bool = False)

A BaseBoard, additional information representing a chess position, and a move stack.

Provides move generation, validation, parsing, attack generation, game end detection, and the capability to make and unmake moves.

The board is initialized to the standard chess starting position, unless otherwise specified in the optional fen argument. If fen is None, an empty board is created.

Optionally supports chess960. In Chess960, castling moves are encoded by a king move to the corresponding rook square. Use chess.Board.from_chess960_pos() to create a board with one of the Chess960 starting positions.

It’s safe to set turn, castling_rights, ep_square, halfmove_clock and fullmove_number directly.

Warning

It is possible to set up and work with invalid positions. In this case, Board implements a kind of “pseudo-chess” (useful to gracefully handle errors or to implement chess variants). Use is_valid() to detect invalid positions.

turn: Color

The side to move (chess.WHITE or chess.BLACK).

castling_rights: Bitboard

Bitmask of the rooks with castling rights.

To test for specific squares:

>>> import chess
>>>
>>> board = chess.Board()
>>> bool(board.castling_rights & chess.BB_H1)  # White can castle with the h1 rook
True

To add a specific square:

>>> board.castling_rights |= chess.BB_A1

Use set_castling_fen() to set multiple castling rights. Also see has_castling_rights(), has_kingside_castling_rights(), has_queenside_castling_rights(), has_chess960_castling_rights(), clean_castling_rights().

fullmove_number: int

Counts move pairs. Starts at 1 and is incremented after every move of the black side.

halfmove_clock: int

The number of half-moves since the last capture or pawn move.

promoted: Bitboard

A bitmask of pieces that have been promoted.

chess960: bool

Whether the board is in Chess960 mode. In Chess960 castling moves are represented as king moves to the corresponding rook square.

ep_square: Square | None

The potential en passant square on the third or sixth rank or None.

Use has_legal_en_passant() to test if en passant capturing would actually be possible on the next move.

move_stack: List[Move]

The move stack. Use Board.push(), Board.pop(), Board.peek() and Board.clear_stack() for manipulation.

property legal_moves: LegalMoveGenerator

A dynamic list of legal moves.

>>> import chess
>>>
>>> board = chess.Board()
>>> board.legal_moves.count()
20
>>> bool(board.legal_moves)
True
>>> move = chess.Move.from_uci("g1f3")
>>> move in board.legal_moves
True

Wraps generate_legal_moves() and is_legal().

property pseudo_legal_moves: PseudoLegalMoveGenerator

A dynamic list of pseudo-legal moves, much like the legal move list.

Pseudo-legal moves might leave or put the king in check, but are otherwise valid. Null moves are not pseudo-legal. Castling moves are only included if they are completely legal.

Wraps generate_pseudo_legal_moves() and is_pseudo_legal().

reset() → None

Restores the starting position.

clear() → None

Clears the board.

Resets move stack and move counters. The side to move is white. There are no rooks or kings, so castling rights are removed.

In order to be in a valid status(), at least kings need to be put on the board.

clear_board() → None

Clears the board.

Board also clears the move stack.

clear_stack() → None

Clears the move stack.

root() → BoardT

Returns a copy of the root position.

ply() → int

Returns the number of half-moves since the start of the game, as indicated by fullmove_number and turn.

If moves have been pushed from the beginning, this is usually equal to len(board.move_stack). But note that a board can be set up with arbitrary starting positions, and the stack can be cleared.

checkers() → SquareSet

Gets the pieces currently giving check.

Returns a set of squares.

is_check() → bool

Tests if the current side to move is in check.

gives_check(move: Move) → bool

Probes if the given move would put the opponent in check. The move must be at least pseudo-legal.

is_variant_end() → bool

Checks if the game is over due to a special variant end condition.

Note, for example, that stalemate is not considered a variant-specific end condition (this method will return False), yet it can have a special result in suicide chess (any of is_variant_loss(), is_variant_win(), is_variant_draw() might return True).

is_variant_loss() → bool

Checks if the current side to move lost due to a variant-specific condition.

is_variant_win() → bool

Checks if the current side to move won due to a variant-specific condition.

is_variant_draw() → bool

Checks if a variant-specific drawing condition is fulfilled.

outcome(*, claim_draw: bool = False) → Outcome | None

Checks if the game is over due to checkmate, stalemate, insufficient material, the seventyfive-move rule, fivefold repetition, or a variant end condition. Returns the chess.Outcome if the game has ended, otherwise None.

Alternatively, use is_game_over() if you are not interested in who won the game and why.

The game is not considered to be over by the fifty-move rule or threefold repetition, unless claim_draw is given. Note that checking the latter can be slow.

is_checkmate() → bool

Checks if the current position is a checkmate.

is_stalemate() → bool

Checks if the current position is a stalemate.

is_insufficient_material() → bool

Checks if neither side has sufficient winning material (has_insufficient_material()).

has_insufficient_material(color: chess.Color) → bool

Checks if color has insufficient winning material.

This is guaranteed to return False if color can still win the game.

The converse does not necessarily hold: The implementation only looks at the material, including the colors of bishops, but not considering piece positions. So fortress positions or positions with forced lines may return False, even though there is no possible winning line.

is_seventyfive_moves() → bool

Since the 1st of July 2014, a game is automatically drawn (without a claim by one of the players) if the half-move clock since a capture or pawn move is equal to or greater than 150. Other means to end a game take precedence.

is_fivefold_repetition() → bool

Since the 1st of July 2014 a game is automatically drawn (without a claim by one of the players) if a position occurs for the fifth time. Originally this had to occur on consecutive alternating moves, but this has since been revised.

can_claim_draw() → bool

Checks if the player to move can claim a draw by the fifty-move rule or by threefold repetition.

Note that checking the latter can be slow.

is_fifty_moves() → bool

Checks that the clock of halfmoves since the last capture or pawn move is greater or equal to 100, and that no other means of ending the game (like checkmate) take precedence.

can_claim_fifty_moves() → bool

Checks if the player to move can claim a draw by the fifty-move rule.

In addition to is_fifty_moves(), the fifty-move rule can also be claimed if there is a legal move that achieves this condition.

can_claim_threefold_repetition() → bool

Checks if the player to move can claim a draw by threefold repetition.

Draw by threefold repetition can be claimed if the position on the board occurred for the third time or if such a repetition is reached with one of the possible legal moves.

Note that checking this can be slow: In the worst case scenario, every legal move has to be tested and the entire game has to be replayed because there is no incremental transposition table.

is_repetition(count: int = 3) → bool

Checks if the current position has repeated 3 (or a given number of) times.

Unlike can_claim_threefold_repetition(), this does not consider a repetition that can be played on the next move.

Note that checking this can be slow: In the worst case, the entire game has to be replayed because there is no incremental transposition table.

push(move: Move) → None

Updates the position with the given move and puts it onto the move stack.

>>> import chess
>>>
>>> board = chess.Board()
>>>
>>> Nf3 = chess.Move.from_uci("g1f3")
>>> board.push(Nf3)  # Make the move

>>> board.pop()  # Unmake the last move
Move.from_uci('g1f3')

Null moves just increment the move counters, switch turns and forfeit en passant capturing.

Warning

Moves are not checked for legality. It is the caller’s responsibility to ensure that the move is at least pseudo-legal or a null move.

pop() → Move

Restores the previous position and returns the last move from the stack.

Raises:

IndexError if the move stack is empty.

peek() → Move

Gets the last move from the move stack.

Raises:

IndexError if the move stack is empty.

find_move(from_square: chess.Square, to_square: chess.Square, promotion: chess.PieceType | None = None) → Move

Finds a matching legal move for an origin square, a target square, and an optional promotion piece type.

For pawn moves to the backrank, the promotion piece type defaults to chess.QUEEN, unless otherwise specified.

Castling moves are normalized to king moves by two steps, except in Chess960.

Raises:

IllegalMoveError if no matching legal move is found.

has_pseudo_legal_en_passant() → bool

Checks if there is a pseudo-legal en passant capture.

has_legal_en_passant() → bool

Checks if there is a legal en passant capture.

fen(*, shredder: bool = False, en_passant: Literal['legal', 'fen', 'xfen'] = 'legal', promoted: bool | None = None) → str

Gets a FEN representation of the position.

A FEN string (e.g., rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1) consists of the board part board_fen(), the turn, the castling part (castling_rights), the en passant square (ep_square), the halfmove_clock and the fullmove_number.

Parameters:

• shredder – Use castling_shredder_fen() and encode castling rights by the file of the rook (like HAha) instead of the default castling_xfen() (like KQkq).

• en_passant – By default, only fully legal en passant squares are included (has_legal_en_passant()). Pass fen to strictly follow the FEN specification (always include the en passant square after a two-step pawn move) or xfen to follow the X-FEN specification (has_pseudo_legal_en_passant()).

• promoted – Mark promoted pieces like Q~. By default, this is only enabled in chess variants where this is relevant.

set_fen(fen: str) → None

Parses a FEN and sets the position from it.

Raises:

ValueError if syntactically invalid. Use is_valid() to detect invalid positions.

set_castling_fen(castling_fen: str) → None

Sets castling rights from a string in FEN notation like Qqk.

Also clears the move stack.

Raises:

ValueError if the castling FEN is syntactically invalid.

chess960_pos(*, ignore_turn: bool = False, ignore_castling: bool = False, ignore_counters: bool = True) → int | None

Gets the Chess960 starting position index between 0 and 956, or None if the current position is not a Chess960 starting position.

By default, white to move (ignore_turn) and full castling rights (ignore_castling) are required, but move counters (ignore_counters) are ignored.

epd(*, shredder: bool = False, en_passant: Literal['legal', 'fen', 'xfen'] = 'legal', promoted: bool | None = None, **operations: None | str | int | float | Move | Iterable[Move]) → str

Gets an EPD representation of the current position.

See fen() for FEN formatting options (shredder, ep_square and promoted).

EPD operations can be given as keyword arguments. Supported operands are strings, integers, finite floats, legal moves and None. Additionally, the operation pv accepts a legal variation as a list of moves. The operations am and bm accept a list of legal moves in the current position.

The name of the field cannot be a lone dash and cannot contain spaces, newlines, carriage returns or tabs.

hmvc and fmvn are not included by default. You can use:

>>> import chess
>>>
>>> board = chess.Board()
>>> board.epd(hmvc=board.halfmove_clock, fmvn=board.fullmove_number)
'rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - hmvc 0; fmvn 1;'

set_epd(epd: str) → Dict[str, None | str | int | float | Move | List[Move]]

Parses the given EPD string and uses it to set the position.

If present, hmvc and fmvn are used to set the half-move clock and the full-move number. Otherwise, 0 and 1 are used.

Returns a dictionary of parsed operations. Values can be strings, integers, floats, move objects, or lists of moves.

Raises:

ValueError if the EPD string is invalid.

san(move: Move) → str

Gets the standard algebraic notation of the given move in the context of the current position.

lan(move: Move) → str

Gets the long algebraic notation of the given move in the context of the current position.

variation_san(variation: Iterable[Move]) → str

Given a sequence of moves, returns a string representing the sequence in standard algebraic notation (e.g., 1. e4 e5 2. Nf3 Nc6 or 37...Bg6 38. fxg6).

The board will not be modified as a result of calling this.

Raises:

IllegalMoveError if any moves in the sequence are illegal.

parse_san(san: str) → Move

Uses the current position as the context to parse a move in standard algebraic notation and returns the corresponding move object.

Ambiguous moves are rejected. Overspecified moves (including long algebraic notation) are accepted. Some common syntactical deviations are also accepted.

The returned move is guaranteed to be either legal or a null move.

Raises:

ValueError (specifically an exception specified below) if the SAN is invalid, illegal or ambiguous.

• InvalidMoveError if the SAN is syntactically invalid.

• IllegalMoveError if the SAN is illegal.

• AmbiguousMoveError if the SAN is ambiguous.

push_san(san: str) → Move

Parses a move in standard algebraic notation, makes the move and puts it onto the move stack.

Returns the move.

Raises:

ValueError (specifically an exception specified below) if neither legal nor a null move.

• InvalidMoveError if the SAN is syntactically invalid.

• IllegalMoveError if the SAN is illegal.

• AmbiguousMoveError if the SAN is ambiguous.

uci(move: Move, *, chess960: bool | None = None) → str

Gets the UCI notation of the move.

chess960 defaults to the mode of the board. Pass True to force Chess960 mode.

parse_uci(uci: str) → Move

Parses the given move in UCI notation.

Supports both Chess960 and standard UCI notation.

The returned move is guaranteed to be either legal or a null move.

Raises:

ValueError (specifically an exception specified below) if the move is invalid or illegal in the current position (but not a null move).

• InvalidMoveError if the UCI is syntactically invalid.

• IllegalMoveError if the UCI is illegal.

push_uci(uci: str) → Move

Parses a move in UCI notation and puts it on the move stack.

Returns the move.

Raises:

ValueError (specifically an exception specified below) if the move is invalid or illegal in the current position (but not a null move).

• InvalidMoveError if the UCI is syntactically invalid.

• IllegalMoveError if the UCI is illegal.

push_xboard(san: str) → Move

Parses a move in standard algebraic notation, makes the move and puts it onto the move stack.

Returns the move.

Raises:

ValueError (specifically an exception specified below) if neither legal nor a null move.

• InvalidMoveError if the SAN is syntactically invalid.

• IllegalMoveError if the SAN is illegal.

• AmbiguousMoveError if the SAN is ambiguous.

is_en_passant(move: Move) → bool

Checks if the given pseudo-legal move is an en passant capture.

is_capture(move: Move) → bool

Checks if the given pseudo-legal move is a capture.

is_zeroing(move: Move) → bool

Checks if the given pseudo-legal move is a capture or pawn move.

is_irreversible(move: Move) → bool

Checks if the given pseudo-legal move is irreversible.

In standard chess, pawn moves, captures, moves that destroy castling rights and moves that cede en passant are irreversible.

This method has false-negatives with forced lines. For example, a check that will force the king to lose castling rights is not considered irreversible. Only the actual king move is.

is_castling(move: Move) → bool

Checks if the given pseudo-legal move is a castling move.

is_kingside_castling(move: Move) → bool

Checks if the given pseudo-legal move is a kingside castling move.

is_queenside_castling(move: Move) → bool

Checks if the given pseudo-legal move is a queenside castling move.

clean_castling_rights() → chess.Bitboard

Returns valid castling rights filtered from castling_rights.

has_castling_rights(color: chess.Color) → bool

Checks if the given side has castling rights.

has_kingside_castling_rights(color: chess.Color) → bool

Checks if the given side has kingside (that is h-side in Chess960) castling rights.

has_queenside_castling_rights(color: chess.Color) → bool

Checks if the given side has queenside (that is a-side in Chess960) castling rights.

has_chess960_castling_rights() → bool

Checks if there are castling rights that are only possible in Chess960.

status() → Status

Gets a bitmask of possible problems with the position.

STATUS_VALID if all basic validity requirements are met. This does not imply that the position is actually reachable with a series of legal moves from the starting position.

Otherwise, bitwise combinations of: STATUS_NO_WHITE_KING, STATUS_NO_BLACK_KING, STATUS_TOO_MANY_KINGS, STATUS_TOO_MANY_WHITE_PAWNS, STATUS_TOO_MANY_BLACK_PAWNS, STATUS_PAWNS_ON_BACKRANK, STATUS_TOO_MANY_WHITE_PIECES, STATUS_TOO_MANY_BLACK_PIECES, STATUS_BAD_CASTLING_RIGHTS, STATUS_INVALID_EP_SQUARE, STATUS_OPPOSITE_CHECK, STATUS_EMPTY, STATUS_RACE_CHECK, STATUS_RACE_OVER, STATUS_RACE_MATERIAL, STATUS_TOO_MANY_CHECKERS, STATUS_IMPOSSIBLE_CHECK.

is_valid() → bool

Checks some basic validity requirements.

See status() for details.

transform(f: Callable[[chess.Bitboard], chess.Bitboard]) → BoardT

Returns a transformed copy of the board (without move stack) by applying a bitboard transformation function.

Available transformations include chess.flip_vertical(), chess.flip_horizontal(), chess.flip_diagonal(), chess.flip_anti_diagonal(), chess.shift_down(), chess.shift_up(), chess.shift_left(), and chess.shift_right().

Alternatively, apply_transform() can be used to apply the transformation on the board.

mirror() → BoardT

Returns a mirrored copy of the board.

The board is mirrored vertically and piece colors are swapped, so that the position is equivalent modulo color. Also swap the “en passant” square, castling rights and turn.

Alternatively, apply_mirror() can be used to mirror the board.

copy(*, stack: bool | int = True) → BoardT

Creates a copy of the board.

Defaults to copying the entire move stack. Alternatively, stack can be False, or an integer to copy a limited number of moves.

classmethod empty(*, chess960: bool = False) → BoardT

Creates a new empty board. Also see clear().

classmethod from_epd(epd: str, *, chess960: bool = False) → Tuple[BoardT, Dict[str, None | str | int | float | Move | List[Move]]]

Creates a new board from an EPD string. See set_epd().

Returns the board and the dictionary of parsed operations as a tuple.

classmethod from_chess960_pos(scharnagl: int) → BoardT

Creates a new board, initialized with a Chess960 starting position.

>>> import chess
>>> import random
>>>
>>> board = chess.Board.from_chess960_pos(random.randint(0, 959))

class chess.BaseBoard(board_fen: str | None = 'rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR')

A board representing the position of chess pieces. See Board for a full board with move generation.

The board is initialized with the standard chess starting position, unless otherwise specified in the optional board_fen argument. If board_fen is None, an empty board is created.

reset_board() → None

Resets pieces to the starting position.

Board also resets the move stack, but not turn, castling rights and move counters. Use chess.Board.reset() to fully restore the starting position.

clear_board() → None

Clears the board.

Board also clears the move stack.

pieces(piece_type: chess.PieceType, color: chess.Color) → SquareSet

Gets pieces of the given type and color.

Returns a set of squares.

piece_at(square: chess.Square) → Piece | None

Gets the piece at the given square.

piece_type_at(square: chess.Square) → chess.PieceType | None

Gets the piece type at the given square.

color_at(square: chess.Square) → chess.Color | None

Gets the color of the piece at the given square.

king(color: chess.Color) → chess.Square | None

Finds the king square of the given side. Returns None if there is no king of that color.

In variants with king promotions, only non-promoted kings are considered.

attacks(square: chess.Square) → SquareSet

Gets the set of attacked squares from the given square.

There will be no attacks if the square is empty. Pinned pieces are still attacking other squares.

Returns a set of squares.

is_attacked_by(color: chess.Color, square: chess.Square) → bool

Checks if the given side attacks the given square.

Pinned pieces still count as attackers. Pawns that can be captured en passant are not considered attacked.

attackers(color: chess.Color, square: chess.Square) → SquareSet

Gets the set of attackers of the given color for the given square.

Pinned pieces still count as attackers.

Returns a set of squares.

pin(color: chess.Color, square: chess.Square) → SquareSet

Detects an absolute pin (and its direction) of the given square to the king of the given color.

>>> import chess
>>>
>>> board = chess.Board("rnb1k2r/ppp2ppp/5n2/3q4/1b1P4/2N5/PP3PPP/R1BQKBNR w KQkq - 3 7")
>>> board.is_pinned(chess.WHITE, chess.C3)
True
>>> direction = board.pin(chess.WHITE, chess.C3)
>>> direction
SquareSet(0x0000_0001_0204_0810)
>>> print(direction)
. . . . . . . .
. . . . . . . .
. . . . . . . .
1 . . . . . . .
. 1 . . . . . .
. . 1 . . . . .
. . . 1 . . . .
. . . . 1 . . .

Returns a set of squares that mask the rank, file or diagonal of the pin. If there is no pin, then a mask of the entire board is returned.

is_pinned(color: chess.Color, square: chess.Square) → bool

Detects if the given square is pinned to the king of the given color.

remove_piece_at(square: chess.Square) → Piece | None

Removes the piece from the given square. Returns the Piece or None if the square was already empty.

Board also clears the move stack.

set_piece_at(square: chess.Square, piece: Piece | None, promoted: bool = False) → None

Sets a piece at the given square.

An existing piece is replaced. Setting piece to None is equivalent to remove_piece_at().

Board also clears the move stack.

board_fen(*, promoted: bool | None = False) → str

Gets the board FEN (e.g., rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR).

set_board_fen(fen: str) → None

Parses fen and sets up the board, where fen is the board part of a FEN.

Board also clears the move stack.

Raises:

ValueError if syntactically invalid.

piece_map(*, mask: chess.Bitboard = 18446744073709551615) → Dict[chess.Square, Piece]

Gets a dictionary of pieces by square index.

set_piece_map(pieces: Mapping[chess.Square, Piece]) → None

Sets up the board from a dictionary of pieces by square index.

Board also clears the move stack.

set_chess960_pos(scharnagl: int) → None

Sets up a Chess960 starting position given its index between 0 and 959. Also see from_chess960_pos().

chess960_pos() → int | None

Gets the Chess960 starting position index between 0 and 959, or None.

unicode(*, invert_color: bool = False, borders: bool = False, empty_square: str = '⭘', orientation: chess.Color = True) → str

Returns a string representation of the board with Unicode pieces. Useful for pretty-printing to a terminal.

Parameters:

• invert_color – Invert color of the Unicode pieces.

• borders – Show borders and a coordinate margin.

transform(f: Callable[[chess.Bitboard], chess.Bitboard]) → BaseBoardT

Returns a transformed copy of the board (without move stack) by applying a bitboard transformation function.

Available transformations include chess.flip_vertical(), chess.flip_horizontal(), chess.flip_diagonal(), chess.flip_anti_diagonal(), chess.shift_down(), chess.shift_up(), chess.shift_left(), and chess.shift_right().

Alternatively, apply_transform() can be used to apply the transformation on the board.

mirror() → BaseBoardT

Returns a mirrored copy of the board (without move stack).

The board is mirrored vertically and piece colors are swapped, so that the position is equivalent modulo color.

Alternatively, apply_mirror() can be used to mirror the board.

copy() → BaseBoardT

Creates a copy of the board.

classmethod empty() → BaseBoardT

Creates a new empty board. Also see clear_board().

classmethod from_chess960_pos(scharnagl: int) → BaseBoardT

Creates a new board, initialized with a Chess960 starting position.

>>> import chess
>>> import random
>>>
>>> board = chess.Board.from_chess960_pos(random.randint(0, 959))

Outcome

class chess.Outcome(termination: Termination, winner: chess.Color | None)

Information about the outcome of an ended game, usually obtained from chess.Board.outcome().

termination: Termination

The reason for the game to have ended.

winner: chess.Color | None

The winning color or None if drawn.

result() → str

Returns 1-0, 0-1 or 1/2-1/2.

class chess.Termination(value)

Enum with reasons for a game to be over.

CHECKMATE = 1

See chess.Board.is_checkmate().

STALEMATE = 2

See chess.Board.is_stalemate().

INSUFFICIENT_MATERIAL = 3

See chess.Board.is_insufficient_material().

SEVENTYFIVE_MOVES = 4

See chess.Board.is_seventyfive_moves().

FIVEFOLD_REPETITION = 5

See chess.Board.is_fivefold_repetition().

FIFTY_MOVES = 6

See chess.Board.can_claim_fifty_moves().

THREEFOLD_REPETITION = 7

See chess.Board.can_claim_threefold_repetition().

VARIANT_WIN = 8

See chess.Board.is_variant_win().

VARIANT_LOSS = 9

See chess.Board.is_variant_loss().

VARIANT_DRAW = 10

See chess.Board.is_variant_draw().

Square sets

class chess.SquareSet(squares: chess.IntoSquareSet = 0)

A set of squares.

>>> import chess
>>>
>>> squares = chess.SquareSet([chess.A8, chess.A1])
>>> squares
SquareSet(0x0100_0000_0000_0001)

>>> squares = chess.SquareSet(chess.BB_A8 | chess.BB_RANK_1)
>>> squares
SquareSet(0x0100_0000_0000_00ff)

>>> print(squares)
1 . . . . . . .
. . . . . . . .
. . . . . . . .
. . . . . . . .
. . . . . . . .
. . . . . . . .
. . . . . . . .
1 1 1 1 1 1 1 1

>>> len(squares)
9

>>> bool(squares)
True

>>> chess.B1 in squares
True

>>> for square in squares:
...     # 0 -- chess.A1
...     # 1 -- chess.B1
...     # 2 -- chess.C1
...     # 3 -- chess.D1
...     # 4 -- chess.E1
...     # 5 -- chess.F1
...     # 6 -- chess.G1
...     # 7 -- chess.H1
...     # 56 -- chess.A8
...     print(square)
...
0
1
2
3
4
5
6
7
56

>>> list(squares)
[0, 1, 2, 3, 4, 5, 6, 7, 56]

Square sets are internally represented by 64-bit integer masks of the included squares. Bitwise operations can be used to compute unions, intersections and shifts.

>>> int(squares)
72057594037928191

Also supports common set operations like issubset(), issuperset(), union(), intersection(), difference(), symmetric_difference() and copy() as well as update(), intersection_update(), difference_update(), symmetric_difference_update() and clear().

add(square: chess.Square) → None

Adds a square to the set.

discard(square: chess.Square) → None

Discards a square from the set.

isdisjoint(other: chess.IntoSquareSet) → bool

Tests if the square sets are disjoint.

issubset(other: chess.IntoSquareSet) → bool

Tests if this square set is a subset of another.

issuperset(other: chess.IntoSquareSet) → bool

Tests if this square set is a superset of another.

remove(square: chess.Square) → None

Removes a square from the set.

Raises:

KeyError if the given square was not in the set.

pop() → chess.Square

Removes and returns a square from the set.

Raises:

KeyError if the set is empty.

clear() → None

Removes all elements from this set.

carry_rippler() → Iterator[chess.Bitboard]

Iterator over the subsets of this set.

mirror() → SquareSet

Returns a vertically mirrored copy of this square set.

tolist() → List[bool]

Converts the set to a list of 64 bools.

classmethod ray(a: chess.Square, b: chess.Square) → SquareSet

All squares on the rank, file or diagonal with the two squares, if they are aligned.

>>> import chess
>>>
>>> print(chess.SquareSet.ray(chess.E2, chess.B5))
. . . . . . . .
. . . . . . . .
1 . . . . . . .
. 1 . . . . . .
. . 1 . . . . .
. . . 1 . . . .
. . . . 1 . . .
. . . . . 1 . .

classmethod between(a: chess.Square, b: chess.Square) → SquareSet

All squares on the rank, file or diagonal between the two squares (bounds not included), if they are aligned.

>>> import chess
>>>
>>> print(chess.SquareSet.between(chess.E2, chess.B5))
. . . . . . . .
. . . . . . . .
. . . . . . . .
. . . . . . . .
. . 1 . . . . .
. . . 1 . . . .
. . . . . . . .
. . . . . . . .

classmethod from_square(square: chess.Square) → SquareSet

Creates a SquareSet from a single square.

>>> import chess
>>>
>>> chess.SquareSet.from_square(chess.A1) == chess.BB_A1
True

Common integer masks are:

chess.BB_EMPTY: chess.Bitboard = 0

chess.BB_ALL: chess.Bitboard = 0xFFFF_FFFF_FFFF_FFFF

Single squares:

chess.BB_SQUARES = [chess.BB_A1, chess.BB_B1, ..., chess.BB_G8, chess.BB_H8]

Ranks and files:

chess.BB_RANKS = [chess.BB_RANK_1, ..., chess.BB_RANK_8]

chess.BB_FILES = [chess.BB_FILE_A, ..., chess.BB_FILE_H]

Other masks:

chess.BB_LIGHT_SQUARES: chess.Bitboard = 0x55AA_55AA_55AA_55AA

chess.BB_DARK_SQUARES: chess.Bitboard = 0xAA55_AA55_AA55_AA55

chess.BB_BACKRANKS = chess.BB_RANK_1 | chess.BB_RANK_8

chess.BB_CORNERS = chess.BB_A1 | chess.BB_H1 | chess.BB_A8 | chess.BB_H8

chess.BB_CENTER = chess.BB_D4 | chess.BB_E4 | chess.BB_D5 | chess.BB_E5