python-chess: a pure Python chess library

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Introduction

python-chess is a pure Python chess library with move generation and validation and handling of common formats. This is the scholars mate in python-chess:

>>> import chess

>>> board = chess.Board()

>>> board.push_san("e4")
Move.from_uci('e2e4')
>>> board.push_san("e5")
Move.from_uci('e7e5')
>>> board.push_san("Qh5")
Move.from_uci('d1h5')
>>> board.push_san("Nc6")
Move.from_uci('b8c6')
>>> board.push_san("Bc4")
Move.from_uci('f1c4')
>>> board.push_san("Nf6")
Move.from_uci('g8f6')
>>> board.push_san("Qxf7")
Move.from_uci('h5f7')

>>> board.is_checkmate()
True

Features

  • Supports Python 2.6+ and Python 3.3+.

    >>> # Python 2 compability for the following examples.
    >>> from __future__ import print_function
    
  • IPython notebook integration. SVG rendering docs.

    https://github.com/niklasf/python-chess/raw/master/docs/ipython.png
  • Supports standard chess and Chess960.

    >>> chess.Board(chess960=True)
    Board('rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1', chess960=True)
    
    >>> chess.Board.from_chess960_pos(330)
    Board('nrqkbbrn/pppppppp/8/8/8/8/PPPPPPPP/NRQKBBRN w KQkq - 0 1', chess960=True)
    
  • Legal move generator and move validation. This includes all castling rules and en passant captures.

    >>> board = chess.Board()
    >>> board.legal_moves  
    <LegalMoveGenerator at 0x... (Na3, Nc3, Nf3, Nh3, a3, b3, c3, d3, e3, f3, g3, h3, a4, b4, c4, d4, e4, f4, g4, h4)>
    >>> chess.Move.from_uci("a8a1") in board.legal_moves
    False
    
  • Make and unmake moves.

    >>> Nf3 = chess.Move.from_uci("g1f3")
    >>> board.push(Nf3) # Make the move
    
    >>> board.pop() # Unmake the last move
    Move.from_uci('g1f3')
    
  • Show a simple ASCII board.

    >>> board = chess.Board("r1bqkb1r/pppp1Qpp/2n2n2/4p3/2B1P3/8/PPPP1PPP/RNB1K1NR b KQkq - 0 4")
    >>> 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
    
  • Detects checkmates, stalemates and draws by insufficient material.

    >>> board.is_stalemate()
    False
    >>> board.is_insufficient_material()
    False
    >>> board.is_game_over()
    True
    >>> board.halfmove_clock
    0
    
  • Detects repetitions. Has a half move clock.

    >>> board.can_claim_threefold_repetition()
    False
    >>> board.halfmove_clock
    0
    >>> board.can_claim_fifty_moves()
    False
    >>> board.can_claim_draw()
    False
    

    With the new rules from July 2014 a game ends drawn (even without a claim) once a fivefold repetition occurs or if there are 75 moves without a pawn push or capture. Other ways of ending a game take precedence.

    >>> board.is_fivefold_repetition()
    False
    >>> board.is_seventyfive_moves()
    False
    
  • Detects checks and attacks.

    >>> board.is_check()
    True
    >>> board.is_attacked_by(chess.WHITE, chess.E8)
    True
    
    >>> attackers = board.attackers(chess.WHITE, chess.F3)
    >>> attackers
    SquareSet(0b100000001000000)
    >>> chess.G2 in attackers
    True
    >>> print(attackers)
    . . . . . . . .
    . . . . . . . .
    . . . . . . . .
    . . . . . . . .
    . . . . . . . .
    . . . . . . . .
    . . . . . . 1 .
    . . . . . . 1 .
    
  • Detects absolute pins and their directions.

    >>> board.is_pinned(chess.BLACK, chess.E8)
    True
    >>> pin = board.pin(chess.BLACK, chess.E8)
    >>> pin
    SquareSet(0b1000000100000010000001000000000000000000000000000000000000000)
    >>> print(pin)
    . . . . 1 . . .
    . . . . . 1 . .
    . . . . . . 1 .
    . . . . . . . 1
    . . . . . . . .
    . . . . . . . .
    . . . . . . . .
    . . . . . . . .
    
  • Parses and creates SAN representation of moves.

    >>> board = chess.Board()
    >>> board.san(chess.Move(chess.E2, chess.E4))
    'e4'
    >>> board.parse_san('Nf3')
    Move.from_uci('g1f3')
    >>> board.variation_san([chess.Move.from_uci(m) for m in ["e2e4", "e7e5", "g1f3"]])
    '1. e4 e5 2. Nf3'
    
  • Parses and creates FENs, extended FENs and Shredder FENs.

    >>> board.fen()
    'rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1'
    >>> board.shredder_fen()
    'rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w HAha - 0 1'
    >>> board = chess.Board("8/8/8/2k5/4K3/8/8/8 w - - 4 45")
    >>> board.piece_at(chess.C5)
    Piece.from_symbol('k')
    
  • Parses and creates EPDs.

    >>> board = chess.Board()
    >>> board.epd(bm=board.parse_uci("d2d4"))
    'rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - bm d4;'
    
    >>> ops = board.set_epd("1k1r4/pp1b1R2/3q2pp/4p3/2B5/4Q3/PPP2B2/2K5 b - - bm Qd1+; id \"BK.01\";")
    >>> ops == {'bm': [chess.Move.from_uci('d6d1')], 'id': 'BK.01'}
    True
    
  • Read Polyglot opening books. Docs.

    >>> import chess.polyglot
    
    >>> book = chess.polyglot.open_reader("data/polyglot/performance.bin")
    
    >>> board = chess.Board()
    >>> main_entry = book.find(board)
    >>> main_entry.move()
    Move.from_uci('e2e4')
    >>> main_entry.weight
    1
    >>> main_entry.learn
    0
    
    >>> book.close()
    
  • Read and write PGNs. Supports headers, comments, NAGs and a tree of variations. Docs.

    >>> import chess.pgn
    
    >>> pgn = open("data/pgn/molinari-bordais-1979.pgn")
    >>> first_game = chess.pgn.read_game(pgn)
    >>> pgn.close()
    
    >>> first_game.headers["White"]
    'Molinari'
    >>> first_game.headers["Black"]
    'Bordais'
    
    >>> # Iterate through the mainline of this embarrasingly short game.
    >>> node = first_game
    >>> while not node.is_end():
    ...     next_node = node.variation(0)
    ...     print(node.board().san(next_node.move))
    ...     node = next_node
    e4
    c5
    c4
    Nc6
    Ne2
    Nf6
    Nbc3
    Nb4
    g3
    Nd3#
    
    >>> # Use a visitor to do the same task.
    >>> class PrintSanVisitor(chess.pgn.BaseVisitor):
    ...     def visit_move(self, board, move):
    ...         print(board.san(move))
    ...
    >>> first_game.accept(PrintSanVisitor())
    e4
    c5
    c4
    Nc6
    Ne2
    Nf6
    Nbc3
    Nb4
    g3
    Nd3#
    
    >>> first_game.headers["Result"]
    '0-1'
    
  • Probe Gaviota endgame tablebases (DTM, WDL). Docs.

    >>> import chess.gaviota
    
    >>> tablebases = chess.gaviota.open_tablebases("data/gaviota")
    
    >>> # White to move mates in 31 half moves in this KRvK endgame.
    >>> board = chess.Board("8/8/8/8/4k3/8/6R1/7K w - - 0 1")
    >>> tablebases.probe_dtm(board)
    31
    
    >>> tablebases.close()
    
  • Probe Syzygy endgame tablebases (DTZ, WDL). Docs.

    >>> import chess.syzygy
    
    >>> tablebases = chess.syzygy.open_tablebases("data/syzygy")
    
    >>> # Black to move is losing in 53 half moves (distance to zero) in this
    >>> # KNBvK endgame.
    >>> board = chess.Board("8/2K5/4B3/3N4/8/8/4k3/8 b - - 0 1")
    >>> tablebases.probe_dtz(board)
    -53
    
    >>> tablebases.close()
    
  • Communicate with an UCI engine. Docs.

    >>> import chess.uci
    
    >>> engine = chess.uci.popen_engine("stockfish")
    >>> engine.uci()
    >>> engine.author  
    'Tord Romstad, Marco Costalba and Joona Kiiski'
    
    >>> # Synchronous mode.
    >>> board = chess.Board("1k1r4/pp1b1R2/3q2pp/4p3/2B5/4Q3/PPP2B2/2K5 b - - 0 1")
    >>> engine.position(board)
    >>> engine.go(movetime=2000) # Gets tuple of bestmove and ponder move.
    BestMove(bestmove=Move.from_uci('d6d1'), ponder=Move.from_uci('c1d1'))
    
    >>> # Asynchronous mode.
    >>> def callback(command):
    ...    bestmove, ponder = command.result()
    ...    assert bestmove == chess.Move.from_uci('d6d1')
    ...
    >>> command = engine.go(movetime=2000, async_callback=callback)
    >>> command.done()
    False
    >>> command.result()
    BestMove(bestmove=Move.from_uci('d6d1'), ponder=Move.from_uci('c1d1'))
    >>> command.done()
    True
    
    >>> # Quit.
    >>> engine.quit()
    0
    

Bug bounty

There is a 100$ bug bounty for the first report of a critical issue in the core module. (Most likely I’ll renew the bounty.) The bug must be reproducible in the latest release, not yet reported, and not yet fixed in the master branch. I consider critical:

  • Move generation
  • Move validation
  • Move making
  • Parser errors that leave objects in an inconsistent state

Performance

Correctness > clean interface > performance.

You can install the gmpy2 or gmpy (https://pypi.python.org/pypi/gmpy2) modules in order to get a slight performance boost on basic operations like bitscans and population counts.

python-chess only imports very basic general (non-chess-related) operations from native libraries. All logic is pure Python. There will always be pure Python fallbacks.

Installing

pip install python-chess

Selected use cases

If you like, let me know if you are creating something intresting with python-chess, for example:

License

python-chess is licensed under the GPL3. See the LICENSE file for the full copyright and license information.

Thanks to Sam Tannous for publishing his approach to avoid rotated bitboards with direct lookup (pdf) alongside his GPL2+ engine Shatranj. Some of the bitboard move generation parts are ported from there.

Thanks to Ronald de Man for his Syzygy endgame tablebases (https://github.com/syzygy1/tb). The probing code in python-chess is very directly ported from his C probing code.

Thanks to Miguel A. Ballicora for his Gaviota tablebases (https://github.com/michiguel/Gaviota-Tablebases).

Indices and tables