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 2.7 and Python 3.3+.

    >>> # Python 2 compability for the following examples.
    >>> from __future__ import print_function
    
  • Supports standard chess and Chess960.

  • Legal move generator and move validation. This includes all castling rules and en-passant captures.

    >>> chess.Move.from_uci("a8a1") in board.legal_moves
    False
    
  • Make and unmake moves.

    >>> Qf7 = board.pop() # Unmake last move (Qf7#)
    >>> Qf7
    Move.from_uci('h5f7')
    
    >>> board.push(Qf7) # Restore
    
  • Show a simple ASCII board.

    >>> 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'
    
  • 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.

    >>> import chess.polyglot
    
    >>> book = chess.polyglot.open_reader("data/opening-books/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.

    >>> import chess.pgn
    
    >>> pgn = open("data/games/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 node.variations:
    ...     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#
    
    >>> first_game.headers["Result"]
    '0-1'
    
  • Probe Syzygy endgame tablebases.

    >>> import chess.syzygy
    
    >>> tablebases = chess.syzygy.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.

    >>> import chess.uci
    >>> import time
    
    >>> 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'))
    
    >>> # Synchronous communication, but search in background.
    >>> engine.go(infinite=True)
    >>> time.sleep(2)
    >>> engine.stop()
    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
    

Peformance

python-chess is not intended to be used by serious chess engines where performance is critical. The goal is rather to create a simple and relatively highlevel library.

You can install the gmpy2 or gmpy (https://code.google.com/p/gmpy/) modules in order to get a slight performance boost on basic operations like bit scans 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

  • With pip:

    sudo pip install python-chess
    
  • From current source code:

    python setup.py sdist
    sudo python setup.py install
    

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 with 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.

Indices and tables