Main Documentation#

class Color#

Represents either White or Black, used to identify the two players and their pieces.

static from_str(name: str) → Color#

Return the color corresponding to name (case‑insensitive).

Parameters:

name (str) – The string "white" or "black" in any case.

Returns:

The matching Color instance.

Return type:

Color

Raises:

ValueError – If name is not recognized.

>>> Color.from_str("White") is WHITE
True
>>> Color.from_str("BLACK") is BLACK
True
property opposite: Color#

Gets the opposite Color to this one.

Returns:

The opposite Color instance.

Return type:

Color

>>> WHITE.opposite is BLACK
True
>>> BLACK.opposite is WHITE
True
__str__() → str#

Serializes a Color to a str of its name in title case.

Returns:

A str of the Color’s name

>>> str(WHITE)
"White"
>>> str(BLACK)
"Black"
__invert__() → Color#

Alias for Color.opposite, Allows ~WHITE syntax.

__hash__() → int#
__repr__() → str#
__eq__(other: Any) → bool#
WHITE: Color#

The white player

BLACK: Color#

The black player

class PieceType#

Represents one of the 6 types of pieces in chess, either a pawn, knight, bishop, rook, queen, or king.

static from_str(piece_type: str) → PieceType#

Return the piece type corresponding to name (case‑insensitive).

Parameters:

name (str) – One of "pawn", "knight", "bishop", "rook", "queen" or "king" (any case).

Return type:

PieceType

Returns:

The matching PieceType.

Raises:

ValueError – If name is not recognized.

>>> PieceType.from_str("pawn") is PAWN
True
>>> PieceType.from_str("kNiGhT") is KNIGHT
True
__str__() → str#

Serializes a PieceType to a str of its name in title case.

>>> str(PAWN)
"Pawn"
>>> str(BISHOP)
"Bishop"
```
__repr__() → str#
__eq__(other: Any) → bool#
__hash__() → int#
PAWN: PieceType#

The PieceType for pawns

KNIGHT: PieceType#

The PieceType for knights

BISHOP: PieceType#

The PieceType for bishops

ROOK: PieceType#

The PieceType for rooks

QUEEN: PieceType#

The PieceType for queens

KING: PieceType#

The PieceType for kings

PIECE_TYPES: list[PieceType]#

A list of all PieceType values. In the order of [PAWN, KNIGHT, BISHOP, ROOK, QUEEN, KING]

class Piece(color: Color, type: PieceType)#

Represents a piece with both a Color and a PieceType, such as a White Pawn, or a Black Rook.

__init__(color: Color, type: PieceType)#

Initialize the Piece with color and type.

Parameters:

  • color (Color) – The owning side.

  • type (PieceType) – The intrinsic kind of the piece.

static from_chr(char: str) → Piece#

Return the piece encoded by char (ASCII piece letter).

Uppercase letters encode WHITE pieces, lowercase letters encode BLACK.

Parameters:

char (str) – One of PRNBQKprnbqk.

Return type:

Piece

Returns:

The corresponding Piece.

Raises:

ValueError – If char is not a valid piece letter.

>>> Piece.from_chr("P")
<Piece: (White, Pawn)>
>>> Piece.from_chr("n")
<Piece: (Black, Knight)>
property piece_type: PieceType#

Gets the PieceType of this Piece.

property color: Color#

Gets the Color of this Piece.

unicode() → str#

Returns Unicode figurine character corresponding to this Piece. 

>>> Piece(WHITE, PAWN).unicode()
"♙"
>>> Piece(BLACK, KNIGHT).unicode()
"♞"
__eq__(other: Any)#

Evaluates to True when compared with another Piece with the same PieceType and Color

__str__() → str#

Serializes a Piece as a single ASCII character str. Uses uppercase for any Piece that is WHITE, and lowercase for any Piece that is BLACK. 

>>> str(Piece(WHITE, PAWN))
"P"
>>> str(Piece(BLACK, KNIGHT))
"n"
__hash__() → int#
class Square#

Represents one of the 64 squares on a chess board.

static from_str(name: str) → Square#

Return the Square encoded by name (case‑insensitive).

Parameters:

name (str) – The name of the square

Return type:

Square

Returns:

The corresponding Square

Raises:

ValueError if given a string which does not represent a Square

>>> Square.from_string("E1") == E1
True
>>> Square.from_string("a2") == A2
Tru
bb() → Bitboard#

Creates a Bitboard containing only this Square. 

>>> A1.bb() == Bitboard([A1])
True
>>> H3.bb() == Bitboard([H3])
True
index() → int#

Returns the index of this Square in the provided SQUARES list.

>>> A1.index()
0
>>> B1.index()
1
>>> A2.index()
8
>>> H8.index()
63
adjacent() → Bitboard#

Creates a Bitboard of all neighbors orthogonal or diagonal to this Square. 

>>> A1.adjacent() == Bitboard([A2, B1, B2])
True
>>> E5.adjacent() == Bitboard([D4, D5, D6, E4, E6, F4, F5, F6])
True
north(distance: int = 1) → Square | None#

Return the square that is the given distance number of ranks above this square.

Parameters:

distance – how many ranks to move north.

Returns:

the target square, or None if it would be off the board.

Return type:

Square | None

>>> B6.north() is B7
True
>>> A1.north(distance=3) is A4
True
>>> B8.north(distance=2)
None
south(distance: int = 1) → Square | None#

Return the square that is the given distance number of ranks below this square.

Parameters:

distance (int, default = 1) – how many ranks to move south.

Returns:

the target square, or None if it would be off the board.

Return type:

Square | None

>>> B6.south() is B5
True
>>> B8.south(distance=2) is B6
True
>>> A1.south(distance=3)
None
east(distance: int = 1) → Square | None#

Return the square that is the given distance number of files to the east of this square.

Parameters:

distance (int, default = 1) – how many files to move east (toward the H-file).

Returns:

the target square, or None if it would be off the board.

Return type:

Square | None

>>> B6.east() is C6
True
>>> A1.east(distance=3) is D1
True
>>> H8.east(distance=2)
None
west(distance: int = 1) → Square | None#

Return the square that is the given distance number of files to the west of this square.

Parameters:

distance (int, default = 1) – how many files to move west (toward the A-file).

Returns:

the target square, or None if it would be off the board.

Return type:

Square | None

>>> B6.west() == A6
True
>>> H8.west(distance=2) == E8
True
>>> A1.west(distance=3)
None
nw(distance: int = 1) → Square | None#

Return the square that is the given distance number of files west and ranks north of this square.

Parameters:

distance (int, default = 1) – number of steps to move north-west.

Returns:

the target square, or None if it would be off the board.

Return type:

Square | None

>>> C3.nw() == B4
True
>>> A1.nw()
None
>>> D4.nw(distance=2) == B6
True
ne(distance: int = 1) → Square | None#

Return the square that is the given distance number of files east and ranks north of this square.

Parameters:

distance (int, default = 1) – number of steps to move north-east.

Returns:

the target square, or None if it would be off the board.

Return type:

Square | None

>>> C3.ne() is D4
True
>>> E4.ne(distance = 2) is G2
True
>>> H8.ne()
None
sw(distance: int = 1) → Square | None#

Return the square that is the given distance number of files west and ranks south of this square.

Parameters:

distance (int, default = 1) – number of steps to move south-west.

Returns:

the target square, or None if it would be off the board.

Return type:

Square | None

>>> C3.sw() is B2
True
>>> E4.sw(distance = 2) is C6
True
>>> A1.sw()
None
se(distance: int = 1) → Square | None#

Return the square that is the given distance number of files east and ranks south of this square.

Parameters:

distance (int, default = 1) – number of steps to move south-east.

Returns:

the target square, or None if it would be off the board.

Return type:

Square | None

>>> C3.se() is D2
True
>>> E4.se(distance = 2) is G6
True
>>> H1.se()
None
__and__(other: Bitboard) → Bitboard#

Return the intersection, in the form of a Bitboard, of this Square and a Bitboard, or another Square.

Parameters:

other (Bitboard) – Bitboard or Square to intersect with

Returns:

squares common to both operands.

Return type:

Bitboard

>>> A1 & Bitboard([A1, A2]) == Bitboard([A1])
True
>>> C_FILE & C1 == Bitboard([C1])
True
>>> B2 & B3 == Bitboard([])
True
>>> G2 & G2 == Bitboard([G2])
True
__or__(other: Bitboard) → Bitboard#

Return the union, in the form of a Bitboard, of this Square and a Bitboard, or another Square.

Parameters:

other (Bitboard) – Bitboard or Square to union with

Returns:

squares common to both operands.

Return type:

Bitboard

>>> A1 | Bitboard([A1, A2]) == Bitboard([A1, A2])
True
>>> Bitboard([B2]) | D1 == Bitboard([B2, D1])
True
>>> B2 | B3 == Bitboard([B2, B3])
True
>>> G2 | G2 == Bitboard([G2])
True
__xor__(other: Bitboard) → Bitboard#

Return the symmetric difference, in the form of a Bitboard, of this Square and a Bitboard, or another Square.

Parameters:

other (Bitboard) – Bitboard or Square to XOR with

Returns:

squares common to both operands.

Return type:

Bitboard

>>> A1 ^ Bitboard([A1, A2]) == Bitboard([A2])
True
>>> Bitboard([B2]) ^ D1 == Bitboard([B2, D1])
True
>>> B2 ^ B3 == Bitboard([B2, B3])
True
>>> G2 ^ G2 == Bitboard([])
True
__eq__(other: Any) → bool#
__hash__() → int#
__str__() → str#
A1: Square#

The A1 Square

B1: Square#

The B1 Square

C1: Square#

The C1 Square

D1: Square#

The D1 Square

E1: Square#

The E1 Square

F1: Square#

The F1 Square

G1: Square#

The G1 Square

H1: Square#

The H1 Square

A2: Square#

The A2 Square

B2: Square#

The B2 Square

C2: Square#

The C2 Square

D2: Square#

The D2 Square

E2: Square#

The E2 Square

F2: Square#

The F2 Square

G2: Square#

The G2 Square

H2: Square#

The H2 Square

A3: Square#

The A3 Square

B3: Square#

The B3 Square

C3: Square#

The C3 Square

D3: Square#

The D3 Square

E3: Square#

The E3 Square

F3: Square#

The F3 Square

G3: Square#

The G3 Square

H3: Square#

The H3 Square

A4: Square#

The A4 Square

B4: Square#

The B4 Square

C4: Square#

The C4 Square

D4: Square#

The D4 Square

E4: Square#

The E4 Square

F4: Square#

The F4 Square

G4: Square#

The G4 Square

H4: Square#

The H4 Square

A5: Square#

The A5 Square

B5: Square#

The B5 Square

C5: Square#

The C5 Square

D5: Square#

The D5 Square

E5: Square#

The E5 Square

F5: Square#

The F5 Square

G5: Square#

The G5 Square

H5: Square#

The H5 Square

A6: Square#

The A6 Square

B6: Square#

The B6 Square

C6: Square#

The C6 Square

D6: Square#

The D6 Square

E6: Square#

The E6 Square

F6: Square#

The F6 Square

G6: Square#

The G6 Square

H6: Square#

The H6 Square

A7: Square#

The A7 Square

B7: Square#

The B7 Square

C7: Square#

The C7 Square

D7: Square#

The D7 Square

E7: Square#

The E7 Square

F7: Square#

The F7 Square

G7: Square#

The G7 Square

H7: Square#

The H7 Square

A8: Square#

The A8 Square

B8: Square#

The B8 Square

C8: Square#

The C8 Square

D8: Square#

The D8 Square

E8: Square#

The E8 Square

F8: Square#

The F8 Square

G8: Square#

The G8 Square

H8: Square#

The H8 Square

SQUARES: list[Square]#

Every defined Square, in the order of [A1, B1, C1, D1, E1, F1, G1, H1, A2, B2, ..., H8].

SQUARES_FLIPPED: list[Square]#

Every defined Square, but flipped to be in the order of [A8, B8, C8, D8, E8, F8, G8, H8, A7, B7, ..., H1].

class Bitboard(squares: Collection[Square])#

A set of squares represented as a 64-bit integer, where each bit indicates whether a Square is included.

__init__(squares: Collection[Square])#

Initialize a Bitboard that contains squares.

Parameters:

squares (Collection[Square]) – squares to include in the new Bitboard.

__str__() → str#

Return a str in which included squares are shown as 1 and excluded squares as 0.

Returns:

an 8×8 grid row-major from A8 to H1.

Return type:

str

>>> print(str(RANK_5))
0 0 0 0 0 0 0 0 
0 0 0 0 0 0 0 0 
0 0 0 0 0 0 0 0 
1 1 1 1 1 1 1 1 
0 0 0 0 0 0 0 0 
0 0 0 0 0 0 0 0 
0 0 0 0 0 0 0 0 
0 0 0 0 0 0 0 0
static from_int(value: int) → Bitboard#

Construct a Bitboard from its integer encoding (see __int__()).

Parameters:

value (int) – 64-bit integer to convert.

Returns:

new Bitboard corresponding to value.

Return type:

Bitboard

Raises:

OverflowError – if value < 0 or value >= 2 ** 64 

>>> Bitboard.from_int(0) == Bitboard([])
True
>>> Bitboard.from_int(1) == Bitboard([A1])
True
>>> Bitboard.from_int(269498368) == Bitboard([E2, E3, E4, D2, F2])
True
>>> Bitboard.from_int(0xFFFF_FFFF_FFFF_FFFF) == FULL_BB
True
__int__() → int#

Return the integer encoding of this Bitboard.

Returns:

64-bit integer with one bit per square.

Return type:

int

>>> int(EMPTY_BB)
0
>>> int(Bitboard([A1]))
1
>>> int(Bitboard([E2, E3, E4, D2, F2]))
269498368
>>> Bitboard.from_int(int(DARK_SQUARE_BB)) == DARK_SQUARE_BB
True
__len__() → int#

Return the number of squares contained in this Bitboard.

Returns:

population count.

Return type:

int

>>> len(Bitboard([]))
0
>>> len(Bitboard([A1, A2]))
2
>>> len(RANK_1)
8
>>> len(FULL_BB)
64
__contains__(square: Square) → bool#

Test whether square is in this Bitboard.

Parameters:

square (Square) – square to test.

Returns:

membership flag.

Return type:

bool

>>> A1 in Bitboard([A1, A2])
True
>>> H3 in FULL_BB
True
>>> C6 in RANK_1
False
__eq__(other: Any) → bool#

Return True if other is a Bitboard with the same squares.

Parameters:

other (Any) – Bitboard to compare.

Returns:

equality flag.

Return type:

bool

>>> Bitboard([A1, A2, A3, A4, A5, A6, A7, A8]) == A_FILE
True
>>> Bitboard([C4]) == Bitboard([C3])
False
__invert__() → Bitboard#

Return the complement of this Bitboard.

Returns:

new Bitboard with opposite membership.

Return type:

Bitboard

>>> FULL_BB == ~EMPTY_BB
True
>>> LIGHT_SQUARE_BB == ~DARK_SQUARE_BB
True
__and__(other: Bitboard | Square) → Bitboard#

Return the intersection of two Bitboards, or a Bitboard with a Square.

Parameters:

other (Bitboard) – Bitboard or Square to intersect with

Returns:

squares common to both operands.

Return type:

Bitboard

>>> Bitboard([A1]) & Bitboard([A1, A2]) == Bitboard([A1])
True
>>> A_FILE & A1 == Bitboard([A1])
True
>>> LIGHT_SQUARE_BB & DARK_SQUARE_BB == EMPTY_BB
True
__or__(other: Bitboard | Square) → Bitboard#

Return the union of two Bitboards, or a Bitboard with a Square.

Parameters:

other (Bitboard) – Bitboard or Square to union with.

Returns:

squares contained in either operand.

Return type:

Bitboard

>>> Bitboard([A1, A2]) | A3  == Bitboard([A1, A2, A3])
True
>>> LIGHT_SQUARE_BB | DARK_SQUARE_BB == FULL_BB
True
__xor__(other: Bitboard | Square) → Bitboard#

Return the symmetric difference of two Bitboards, or of a Bitboard with a Square.

Parameters:

other (Bitboard) – Bitboard or Square to XOR with.

Returns:

squares in exactly one operand.

Return type:

Bitboard

>>> Bitboard([A1, A2]) ^ A1 == Bitboard([A2])
True
>>> LIGHT_SQUARE_BB ^ DARK_SQUARE_BB == FULL_BB
True
__bool__() → bool#

Return True if the Bitboard is non-empty.

Returns:

truth value.

Return type:

bool

>>> bool(Bitboard([]))
False
>>> bool(EMPTY_BB)
False
>>> bool(Bitboard([A1]))
True
__iter__() → Iterator[Square]#

Iterate over included squares from A1 upward.

__repr__() → str#
__hash__() → int#
RANK_1: Bitboard#

Bitboard containing every square on Rank 1

RANK_2: Bitboard#

Bitboard containing every square on Rank 2

RANK_3: Bitboard#

Bitboard containing every square on Rank 3

RANK_4: Bitboard#

Bitboard containing every square on Rank 4

RANK_5: Bitboard#

Bitboard containing every square on Rank 5

RANK_6: Bitboard#

Bitboard containing every square on Rank 6

RANK_7: Bitboard#

Bitboard containing every square on Rank 7

RANK_8: Bitboard#

Bitboard containing every square on Rank 8

RANKS: list[Bitboard]#

List of the eight rank Bitboard values in order, from RANK_1 to RANK_8.

A_FILE: Bitboard#

Bitboard containing every square on the A-file.

B_FILE: Bitboard#

Bitboard containing every square on the B-file.

C_FILE: Bitboard#

Bitboard containing every square on the C-file.

D_FILE: Bitboard#

Bitboard containing every square on the D-file.

E_FILE: Bitboard#

Bitboard containing every square on the E-file.

F_FILE: Bitboard#

Bitboard containing every square on the F-file

G_FILE: Bitboard#

Bitboard containing every square on the G-file.

H_FILE: Bitboard#

Bitboard containing every square on the H-file.

FILES: list[Bitboard]#

List of the eight file Bitboard values in order, from A_FILE to H_FILE.

FULL_BB: Bitboard#

Bitboard containing all 64 squares

EMPTY_BB: Bitboard#

Bitboard containing no squares

LIGHT_SQUARE_BB: Bitboard#

Bitboard of all light colored squares (B1, D1, etc.)

DARK_SQUARE_BB: Bitboard#

Bitboard of all dark colored squares (A1, C1, etc.)

class CastlingType#

One of four legal castling options: the king moves either kingside or queenside for WHITE or BLACK.

static from_chr(castling_type: str) → CastlingType#

Return the castling type corresponding to a single-character code.

Parameters:

castling_type (str) – one of "K", "Q", "k", "q".

Returns:

the matching CastlingType.

Return type:

CastlingType

Raises:

ValueError – if castling_type is not a valid code.

>>> CastlingType.from_chr("K") is WHITE_KINGSIDE
True
>>> CastlingType.from_chr("Q") is WHITE_QUEENSIDE
True
>>> CastlingType.from_chr("k") is BLACK_KINGSIDE
True
>>> CastlingType.from_chr("q") is BLACK_QUEENSIDE
True
__str__() → str#

Return the one-character code for this castling type.

Returns:

"K", "Q", "k", or "q".

Return type:

str

>>> str(WHITE_KINGSIDE)
'K'
>>> str(WHITE_QUEENSIDE)
'Q'
>>> str(BLACK_KINGSIDE)
'k'
>>> str(BLACK_QUEENSIDE)
'q'
__eq__(other: Any) → bool#

Return True if other is the same castling type.

Parameters:

other (Any) – object to compare.

Returns:

equality flag.

Return type:

bool

__repr__() → str#
__hash__() → int#
WHITE_KINGSIDE: CastlingType#

Castling type representing WHITE kingside castling.

WHITE_QUEENSIDE: CastlingType#

Castling type representing WHITE queenside castling.

BLACK_KINGSIDE: CastlingType#

Castling type representing BLACK kingside castling.

BLACK_QUEENSIDE: CastlingType#

Castling type representing BLACK queenside castling.

class Move(origin: Square, destination: Square, promote_to: PieceType | None = None)#

A chess move, defined by its origin and destination squares and an optional promotion piece type.

__init__(origin: Square, destination: Square, promote_to: PieceType | None = None)#

Create a move from origin to destination.

Parameters:

  • origin (Square) – square the piece starts on.

  • destination (Square) – square the piece ends on.

  • promote_to (PieceType | None) – piece type to promote to, if any.

Raises:

ValueError if the specified origin, destination, and promtion is illegal for every piece for every position.

static castle(castling_type: CastlingType) → Move#

Return the move corresponding to castling_type.

Parameters:

castling_type (CastlingType) – one of the four castling constants.

Returns:

appropriate king move for that castling.

Return type:

Move 

>>> Move.castle(WHITE_KINGSIDE) == Move(E1, G1)
True
>>> Move.castle(WHITE_QUEENSIDE) == Move(E1, C1)
True
>>> Move.castle(BLACK_KINGSIDE) == Move(E8, G8)
True
>>> Move.castle(BLACK_QUEENSIDE) == Move(E8, C8)
True
static from_uci(uci: str) → Move | None#

Parse a UCI long-algebraic str and build a move.

Null moves are supported as “0000”, and are represented as None.

Parameters:

uci (str) – UCI string such as "e2e4" or "b7b8q".

Returns:

move instance, or None for a null move.

Return type:

Move | None

Raises:

ValueError – if uci is malformed or illegal.

>>> Move.from_uci("e2e4") == Move(E2, E4)
True
>>> Move.from_uci("a1d4") == Move(A1, D4)
True
>>> Move.from_uci("b7b8q") == Move(B7, B8, promote_to=QUEEN)
True
>>> Move.from_uci("0000") is None
True
static from_san(san: str, board: Board) → Move#

Parse a SAN str in the context of board.

Parameters:

  • san (str) – SAN text (e.g. "Nf6", "O-O", "e4").

  • board (Board) – position used to disambiguate the SAN.

Returns:

the corresponding move.

Return type:

Move

Raises:

ValueError – if san is invalid for board.

>>> Move.from_san("e4", Board()) == Move(E2, E4)
True
>>> FEN = "r1bqkbnr/pppp1ppp/2n5/4p3/2B1P3/5N2/PPPP1PPP/RNBQK2R b KQkq - 3 3"
>>> board = Board.from_fen(FEN)
>>> Move.from_san("Nf6", board) == Move(G8, F6)
True
san(board: Board) → str#

Return this move in SAN notation relative to board.

Parameters:

board (Board) – position that provides context.

Returns:

SAN string.

Return type:

str

Raises:

ValueError – if the move is illegal for board.

>>> Move(E2, E4).san(Board())
'e4'
>>> FEN = "r1bqkb1r/pppp1ppp/2n2n2/4p3/2B1P3/5N2/PPPP1PPP/RNBQK2R w KQkq - 4 4"
>>> Move(E1, G1).san(Board.from_fen(FEN))
'O-O'
uci() → str#

Return a str of the UCI long algebraic notation representation of this move.

Returns:

UCI string.

Return type:

str

>>> Move(E2, E4).uci()
'e2e4'
>>> Move(A1, D4).uci()
'a1d4'
>>> Move(B7, B8, promote_to=QUEEN).uci()
'b7b8q'
__str__() → str#

Alias for Move.uci(). 

>>> str(Move(E2, E4))
'e2e4'
>>> str(Move(A1, D4))
'a1d4'
>>> str(Move(B7, B8, promote_to=QUEEN))
'b7b8q'
property origin: Square#

The Square the piece moves from.

>>> Move(E2, E4).origin is E2
True
>>> Move.from_uci("a1d4").origin is A1
True
property destination: Square#

The Square the piece moves to.

>>> Move(E2, E4).destination is E4
True
>>> Move.from_uci("a1d4").destination is D4
True
property promotion: PieceType | None#

Promotion PieceType, or None for a non-promotion.

>>> Move.from_uci("b7b8q").promotion is QUEEN
True
>>> Move(E2, E4).promotion is None
True
is_promotion() → bool#

Return True if the move is a promotion.

>>> Move.from_uci("b7b8q").is_promotion()
True
>>> Move(E2, E4).is_promotion()
False
is_capture(board: Board) → bool#

Return True if the move captures a piece on board.

Parameters:

board (Board) – position to check if this is a capture.

Returns:

capture flag.

Return type:

bool

>>> FEN = "r1bqkbnr/pppp1ppp/2n5/4p3/4P3/5N2/PPPP1PPP/RNBQKB1R w KQkq - 2 3"
>>> board = Board.from_fen(FEN)
>>> Move(F3, E5).is_capture(board)
True
is_castling(board: Board) → bool#

Return True if the move is a legal castling move on board.

Parameters:

board (Board) – position to check if this is a castling move.

Returns:

castling flag.

Return type:

bool

>>> FEN = "r1bqkb1r/pppp1ppp/2n2n2/4p3/2B1P3/5N2/PPPP1PPP/RNBQK2R w KQkq - 4 4"
>>> board = Board.from_fen(FEN)
>>> Move(E1, G1).is_castling(board)
True
>>> Move(E1, G1).is_castling(Board.empty())
False
castling_type(board: Board) → CastlingType | None#

If the move is castling, return its type; otherwise None.

Parameters:

board (Board) – position used for classification.

Returns:

corresponding castling type or None.

Return type:

CastlingType | None

>>> FEN = "r1bqkb1r/pppp1ppp/2n2n2/4p3/2B1P3/5N2/PPPP1PPP/RNBQK2R w KQkq - 4 4"
>>> board = Board.from_fen(FEN)
>>> Move(E1, G1).castling_type(board) is WHITE_KINGSIDE
True
>>> Move(E1, G1).castling_type(Board.empty()) is None
True
__eq__(other: Any) → bool#

Return True if other has the same origin, destination and promotion value.

Parameters:

other (Any) – object to compare.

Returns:

equality flag.

Return type:

bool

>>> Move(E2, E4) == Move.from_uci("e2e4")
True
>>> Move(A7, A8) == Move.from_uci("a7a8q")
False
__hash__() → int#
__repr__() → str#
class CastlingRights(castling_types: Collection[CastlingType])#

A set of CastlingType values that encodes a Board’s castling permissions.

__init__(castling_types: Collection[CastlingType]) → None#

Initialize the object with castling_types.

Parameters:

castling_types (Collection[CastlingType]) – iterable of castling constants to include.

static from_fen(castling_fen: str) → CastlingRights#

Build a CastlingRights object from a FEN castling field.

Parameters:

castling_fen (str) – "KQkq", "KQ", "-" …

Returns:

rights object matching castling_fen.

Return type:

CastlingRights

Raises:

ValueError – if castling_fen is not valid FEN.

>>> CastlingRights.from_fen("KQkq") == ALL_CASTLING
True
>>> CastlingRights.from_fen("Qk") == CastlingRights([WHITE_QUEENSIDE, BLACK_KINGSIDE])
True
>>> CastlingRights.from_fen("-") == NO_CASTLING
True
fen() → str#

Returns the Forsyth-Edwards Notation str represetnation of this CastlingRights.

Returns:

"KQkq", "-" or similar.

Return type:

str

>>> NO_CASTLING.fen()
'-'
>>> CastlingRights([WHITE_KINGSIDE, WHITE_QUEENSIDE]).fen()
'KQ'
>>> ALL_CASTLING.fen()
'KQkq'
__contains__(castling_type: CastlingType) → bool#

Return True if castling_type is present.

Parameters:

castling_type (CastlingType) – entry to test.

Returns:

membership flag.

Return type:

bool

>>> WHITE_KINGSIDE in ALL_CASTLING
True
>>> BLACK_KINGSIDE in CastlingRights([WHITE_QUEENSIDE])
False
__iter__() → Iterator[CastlingType]#

Iteratator over included CastlingType values

__len__() → int#

The number of castling types included

__bool__() → CastlingRights#

Returns True if any castling rights are present, alias for CastlingRights.any()

__add__(other: CastlingRights) → CastlingRights#

Return the union of two castling-rights sets.

Parameters:

other (CastlingRights) – rights to add.

Returns:

combined rights.

Return type:

CastlingRights

>>> CastlingRights.from_fen("KQ") + CastlingRights.from_fen("kq") == ALL_CASTLING
True
__eq__(other: Any) → bool#

Return True if other has the identical rights set.

__le__(other: CastlingRights) → bool#

Return True if this set is a subset of other.

>>> CastlingRights.from_fen("KQ") <= CastlingRights.from_fen("KQkq")
True
>>> CastlingRights.from_fen("KQkq") <= CastlingRights.from_fen("KQkq")
True
__lt__(other: CastlingRights) → bool#

Return True if this set is a strict subset of other.

>>> CastlingRights.from_fen("KQ") < CastlingRights.from_fen("KQkq")
True
>>> CastlingRights.from_fen("KQkq") < CastlingRights.from_fen("KQkq")
False
__gt__(other: CastlingRights) → bool#

Return True if this set is a strict superset of other.

>>> CastlingRights.from_fen("KQkq") > CastlingRights.from_fen("KQ")
True
>>> CastlingRights.from_fen("KQkq") > CastlingRights.from_fen("KQkq")
False
__ge__(other: CastlingRights) → bool#

Return True if this set is a superset of, or equal to, other.

>>> CastlingRights.from_fen("KQkq") >= CastlingRights.from_fen("KQ")
True
>>> CastlingRights.from_fen("KQkq") >= CastlingRights.from_fen("KQkq")
True
__str__() → str#

Alias for CastlingRights.fen()

Returns:

"KQkq", "-" or similar.

Return type:

str

>>> str(NO_CASTLING)
'-'
>>> str(CastlingRights([WHITE_KINGSIDE, WHITE_QUEENSIDE]))
'KQ'
>>> str(ALL_CASTLING)
'KQkq'
full(color: Color | None = None) → bool#

Return True if all relevant rights are present.

Parameters:

color (Color | None) – optionally restrict the check to WHITE or BLACK.

Returns:

completeness flag.

Return type:

bool

>>> ALL_CASTLING.full()
True
>>> CastlingRights.from_fen("KQk").full()
False
>>> CastlingRights.from_fen("KQk").full(WHITE)
True
>>> NO_CASTLING.full()
False
any(color: Color | None = None) → bool#

Return True if any castling right is present.

Parameters:

color (Color | None) – optionally restrict the check to WHITE or BLACK.

Returns:

presence flag.

Return type:

bool

>>> ALL_CASTLING.any()
True
>>> CastlingRights.from_fen("KQk").any()
True
>>> CastlingRights.from_fen("K").any()
True
>>> CastlingRights.from_fen("K").any(BLACK)
False
>>> NO_CASTLING.any()
False
kingside(color: Color | None = None) → bool#

Return True if any kingside right is present.

Parameters:

color (Color | None) – optionally restrict the check to WHITE or BLACK.

Returns:

kingside flag.

Return type:

bool

>>> ALL_CASTLING.kingside()
True
>>> CastlingRights.from_fen("Q").kingside()
False
>>> CastlingRights.from_fen("K").kingside()
True
>>> CastlingRights.from_fen("K").kingside(BLACK)
False
>>> NO_CASTLING.kingside()
False
queenside(color: Color | None = None) → bool#

Return True if any queenside right is present.

Parameters:

color (Color | None) – optionally restrict the check to WHITE or BLACK.

Returns:

queenside flag.

Return type:

bool

>>> ALL_CASTLING.queenside()
True
>>> CastlingRights.from_fen("Q").queenside()
True
>>> CastlingRights.from_fen("K").queenside()
False
>>> CastlingRights.from_fen("Q").queenside(BLACK)
False
>>> NO_CASTLING.queenside()
False
__repr__() → str#
__hash__() → int#
ALL_CASTLING: CastlingRights#

Castling rights which include all types of castling

NO_CASTLING: CastlingRights#

Castling rights which include no types of castling

class Board#

A mutable chess position.

A Board represents a configuration of chess pieces as a mapping of each Square to optional an Piece. The Board class includes attributes for CastlingRights, the existence of an en-passant Square, and the Color for the turn of the current player. Also holds the half-move clock and full-move number each as an int.

The Board class provides an interface for generating Move objects representing legal actions for a turn, as well as applying and undoing these moves.

__init__()#

Initializes a Board representing the starting position.

static from_fen(fen: str) → Board#

Build a board from a str of a Forsyth-Edwards Notation (FEN) representation of a position.

The FEN is not required to include a halfmove clock or fullmove number. The default values for these are 0 and 1.

Parameters:

fen (str) – full FEN record.

Returns:

board represented by fen.

Return type:

Board

Raises:

ValueError – if fen is malformed.

>>> board = Board.from_fen("rnbqkbnr/pp1ppppp/8/2p5/4P3/5N2/PPPP1PPP/RNBQKB1R b KQkq - 1 2")
>>> print(board)
r n b q k b n r 
p p - p p p p p 
- - - - - - - - 
- - p - - - - - 
- - - - P - - - 
- - - - - N - - 
P P P P - P P P 
R N B Q K B - R
static empty() → Board#

Creates a completely empty Board, with no pieces on it.

Returns:

An empty position

Return type:

:class:Board

property turn: Color#

Side to move, either WHITE or BLACK.

property halfmove_clock: int#

Gets the current halfmove clock as an int. This represents the number of ply that have passed since a capture or pawn advance.

property fullmove_number: int#

Gets the current fullmove number as an int. This represents the total number of turns each player has taken since the start of a game.

property en_passant_square: Square | None#

Gets the current en passant Square, if it exists. Otherwise returns None.

property castling_rights: CastlingRights#

Gets the current CastlingRights of this Board.

legal_moves() → list[Move]#

Generates a list of legal Move objects for this Board’s position.

Returns:

A list of legal moves for this position.

Return type:

list[Move]

>>> Board().legal_moves()
[<Move: b1a3>, <Move: b1c3>, <Move: g1f3>, <Move: g1h3>, <Move: a2a3>, <Move: a2a4>, <Move: b2b3>, <Move: b2b4>, <Move: c2c3>, <Move: c2c4>, <Move: d2d3>, <Move: d2d4>, <Move: e2e3>, <Move: e2e4>, <Move: f2f3>, <Move: f2f4>, <Move: g2g3>, <Move: g2g4>, <Move: h2h3>, <Move: h2h4>]
apply(move: Move | None) → None#

Applies the given Move to this Board.

The Move argument is not checked to be legal outside of checking if the origin has a Piece. None can be passed as the argument to skip a turn.

Parameters:

move (Move | None) – The move to apply, or None for a null move.

Raises:

ValueError – if the origin of move does not have a piece.

>>> board = Board()
>>> board.apply(Move(E2, E4))
>>> print(board)
r n b q k b n r 
p p p p p p p p 
- - - - - - - - 
- - - - - - - - 
- - - - P - - - 
- - - - - - - - 
P P P P - P P P 
R N B Q K B N R
Raises:

ValueError if the given Move’s origin is an empty square.

undo() → Move | None#

Undoes the last Move applied to this Board.

Returns:

The last move applied to this board.

Return type:

Move | None

Raises:

AttributeError if there are no moves to undo. This is true when Board.history has a len() of 0

>>> board = Board()
>>> board.apply(Move(E2, E4))
>>> board.apply(Move(E7, E5))
>>> board.undo() == Move(E7, E5)
True
>>> print(board)
r n b q k b n r 
p p p p p p p p 
- - - - - - - - 
- - - - - - - - 
- - - - P - - - 
- - - - - - - - 
P P P P - P P P 
R N B Q K B N R
Raises:

AttributeError if there are no moves to undo.

fen() → str#

Gets the Forsyth-Edwards Notation representation as a str of this Board.

Returns:

A FEN representing the position

Return type:

str

>>> board = Board()
>>> board.fen()
'rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1'
copy() → Board#

Returns a new Board which is an exact copy of this Board, including its Move history.

Returns:

A deep copy of this position and its state.

Return type:

Board

__getitem__(none: None) → Bitboard#
__getitem__(square: Square) → Piece | None#
__getitem__(piece_type: PieceType) → Bitboard#
__getitem__(color: Color) → Bitboard#
__getitem__(piece: Piece) → Bitboard#
__getitem__(piece_tuple: tuple[Color, PieceType]) → Bitboard#

Index a Board with a value. Can either index with a Square, None, a PieceType, a Color, a tuple[Color, PieceType], or a Piece,

If given a Square, returns the Piece at the square, or None if the square is unoccupied.

>>> board = Board()
>>> board[E2] is Piece(WHITE, PAWN)
True
>>> board[E4] is None
True

If given None, returns a Bitboard of all empty squares.

>>> board = Board()
>>> print(board[None])
0 0 0 0 0 0 0 0 
0 0 0 0 0 0 0 0 
1 1 1 1 1 1 1 1 
1 1 1 1 1 1 1 1 
1 1 1 1 1 1 1 1 
1 1 1 1 1 1 1 1 
0 0 0 0 0 0 0 0 
0 0 0 0 0 0 0 0

If given a Color, returns a Bitboard of all squares with a piece of that color

>>> board = Board()
>>> print(board[WHITE])
0 0 0 0 0 0 0 0 
0 0 0 0 0 0 0 0 
0 0 0 0 0 0 0 0 
0 0 0 0 0 0 0 0 
0 0 0 0 0 0 0 0 
0 0 0 0 0 0 0 0 
1 1 1 1 1 1 1 1 
1 1 1 1 1 1 1 1

If given a PieceType, returns a Bitboard of all squares with a piece of that type.

>>> board = Board()
>>> print(board[PAWN])
0 0 0 0 0 0 0 0 
1 1 1 1 1 1 1 1 
0 0 0 0 0 0 0 0 
0 0 0 0 0 0 0 0 
0 0 0 0 0 0 0 0 
0 0 0 0 0 0 0 0 
1 1 1 1 1 1 1 1 
0 0 0 0 0 0 0 0

If given a Piece or a tuple of a Color and a PieceType, returns a Bitboard of all squares with matching pieces.

>>> board = Board()
>>> board[WHITE, PAWN] == board[Piece(WHITE, PAWN)]
True
>>> print(board[WHITE, PAWN])
0 0 0 0 0 0 0 0 
0 0 0 0 0 0 0 0 
0 0 0 0 0 0 0 0 
0 0 0 0 0 0 0 0 
0 0 0 0 0 0 0 0 
0 0 0 0 0 0 0 0 
1 1 1 1 1 1 1 1 
0 0 0 0 0 0 0 0
__setitem__(square: Square, piece: Piece | None)#

Sets this Board to have the given Piece and the indexed Square . If set to None, the Square becomes empty.

>>> board = Board()
>>> board[E2] = None
>>> board[E4] = Piece(WHITE, PAWN)
>>> print(board)
r n b q k b n r 
p p p p p p p p 
- - - - - - - - 
- - - - - - - - 
- - - - P - - - 
- - - - - - - - 
P P P P - P P P 
R N B Q K B N R
__delitem__(square: Square)#

Deletes any Piece at the specified Square, leaving the Square empty.

>>> board = Board()
>>> del board[E2]
>>> print(board)
r n b q k b n r 
p p p p p p p p 
- - - - - - - - 
- - - - - - - - 
- - - - - - - - 
- - - - - - - - 
P P P P - P P P 
R N B Q K B N R
__eq__(other: Any) → bool#

Returns True if compared with another Board with the same mapping of Square to Piece objects, equvilent CastlingRights, en-passant Square values, and halfmove and fullmove clocks.

To check if two Board instances are “legally” equal, as in in terms of all of the above besides the halfmove and fullmove clocks, use utils.legally_equal()

Two boards may be considered equal despite having different move histories.

__hash__() → int#

Performs a Zobrist hash of this Board.

__contains__(piece: Piece | None) → bool#

Returns True if this Board has the specified Piece. When given None, returns True if there are any empy squares.

property history: list[Move]#

Gets a list of Move objects of every Move which have been used with Board.apply() and have not been undone with Board.undo() for this Board 

>>> board = Board()
>>> board.apply(Move(E2, E4))
>>> board.apply(Move(E7, E5))
>>> board.apply(Move(G1, F3))
>>> board.history
[<Move: e2e4>, <Move: e7e5>, <Move: g1f3>]
__str__()#

Returns an ASCII str representation of this Board. 

>>> print(str(Board()))
r n b q k b n r 
p p p p p p p p 
- - - - - - - - 
- - - - - - - - 
- - - - - - - - 
- - - - - - - - 
P P P P P P P P 
R N B Q K B N R 

>>> FEN = "rnb3r1/R3Q3/2p5/1p1k1p1r/1n1P4/8/4P3/2K2B1r b - - 3 69"
>>> board = Board.from_fen(FEN)
>>> print(str(board))
r n b - - - r - 
R - - - Q - - - 
- - p - - - - - 
- p - k - p - r 
- n - P - - - - 
- - - - - - - - 
- - - - P - - - 
- - K - - B - r
pretty(color_scheme: Board = Board.OAK, highlighted_squares: Bitboard = EMPTY_BB, targeted_squares: Bitboard = EMPTY_BB) → str#

A pretty to-string method for terminal outputs.

Creates a str representation of this Board using Unicode chess figurines and the provided Board.ColorScheme as a palette for the background and highlights. Bitboard’s can be specified for highlighting particular squares, as for example a Move’s origin, as well as for targetting certain squares, as for possible Move destinations.

Returns:

A rendering of this position as a UTF-8 string with ANSI color codes

Return type:

str

class ColorScheme#

A pallete of colors to be used with Board.pretty() to stylize printed boards.

LAGOON: Board.ColorScheme#

A light blue color pallete

SLATE: Board.ColorScheme#

A slightly purplish, grey color pallete

OAK: Board.ColorScheme#

A classical, wood styled color pallete

WALNUT: Board.ColorScheme#

A less saturated wood styled color pallete

GREEN: Board.ColorScheme#

A familiar green and white color pallete

ROSE: Board.ColorScheme#

A pinkish red color pallete

CLAY: Board.ColorScheme#

A dulled, rosy brown and grey color pallete

STEEL: Board.ColorScheme#

A monochromatic grey color pallete

class BoardStatus#

A predicate-like object that answers the question “is this board in status X?” Examples of statuses include check, check-mate, stalemate, and repetition or 50-move draw claims.

__contains__(board: Board) → bool#

Return True if board satisfies this status.

Parameters:

board (Board) – position to test.

Returns:

membership flag.

Return type:

bool

Examples#

>>> Board() in DRAW
False
>>> FEN = "r1bqkb1r/pppp1Qpp/2n2n2/4p3/2B1P3/8/PPPP1PPP/RNB1K1NR b KQkq - 0 4"
>>> board = Board.from_fen(FEN)
>>> print(board)
r - b q k b - r 
p p p p - Q p p 
- - n - - n - - 
- - - - p - - - 
- - B - P - - - 
- - - - - - - - 
P P P P - P P P 
R N B - K - N R 

>>> board in CHECKMATE
True
__repr__() → str#
__eq__(other: Any) → bool#
CHECK: BoardStatus#

The side to move is in check

MATE: BoardStatus#

The side to move has no legal moves.

CHECKMATE: BoardStatus#

The side to move is in checkmate. The player is in check and has no legal moves.

STALEMATE: BoardStatus#

The side to move is in stalemate. The player has no legal moves but is not in check.

INSUFFICIENT_MATERIAL: BoardStatus#

There is not enough material for either player to be placed in checkmate.

FIFTY_MOVE_TIMEOUT: BoardStatus#

Fifty full-moves have passed without a pawn move or capture.

SEVENTY_FIVE_MOVE_TIMEOUT: BoardStatus#

Seventy five full-moves have passed without a pawn move or capture.

THREEFOLD_REPETITION: BoardStatus#

The same position has occured at least three times.

FIVEFOLD_REPETITION: BoardStatus#

The same position has occured at least five times.

DRAW: BoardStatus#

Any position in which a player may claim a draw. This includes stalemate, insufficient material, a fifty move timeout, or threefold repetition.

FORCED_DRAW: BoardStatus#

A forced draw. This includes stalemate, insufficient material, a seventy five move timeout, or fivefold repetition.

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