python-chess: a pure Python chess library

Introduction

python-chess is a pure Python chess library with move generation, move validation and support for common formats. This is the Scholar's mate in python-chess:

>>> import chess

>>> board = chess.Board()

>>> board.legal_moves  # doctest: +ELLIPSIS
<LegalMoveGenerator at ... (Nh3, Nf3, Nc3, Na3, h3, g3, f3, e3, d3, c3, ...)>
>>> chess.Move.from_uci("a8a1") in board.legal_moves
False

>>> 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

>>> board
Board('r1bqkb1r/pppp1Qpp/2n2n2/4p3/2B1P3/8/PPPP1PPP/RNB1K1NR b KQkq - 0 4')

Documentation

• Core
• PGN parsing and writing
• Polyglot opening book reading
• Gaviota endgame tablebase probing
• Syzygy endgame tablebase probing
• UCI/XBoard engine communication
• Variants
• Changelog

Features

• Supports Python 3.7+ and PyPy3. Includes mypy typings.

• IPython/Jupyter Notebook integration. SVG rendering docs.

  >>> board  # doctest: +SKIP

  

• Chess variants: Standard, Chess960, Suicide, Giveaway, Atomic, King of the Hill, Racing Kings, Horde, Three-check, Crazyhouse. Variant docs.

• 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

• 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 as a draw (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(0x0000_0000_0000_4040)
  >>> chess.G2 in attackers
  True
  >>> print(attackers)
  . . . . . . . .
  . . . . . . . .
  . . . . . . . .
  . . . . . . . .
  . . . . . . . .
  . . . . . . . .
  . . . . . . 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

• Detects absolute pins and their directions.

• Reads 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
  
  >>> book.close()

• Reads and writes PGNs. Supports headers, comments, NAGs and a tree of variations. Docs.

  >>> import chess.pgn
  
  >>> with open("data/pgn/molinari-bordais-1979.pgn") as pgn:
  ...     first_game = chess.pgn.read_game(pgn)
  
  >>> first_game.headers["White"]
  'Molinari'
  >>> first_game.headers["Black"]
  'Bordais'
  
  >>> first_game.mainline()  # doctest: +ELLIPSIS
  <Mainline at ... (1. e4 c5 2. c4 Nc6 3. Ne2 Nf6 4. Nbc3 Nb4 5. g3 Nd3#)>
  
  >>> first_game.headers["Result"]
  '0-1'

• Probe Gaviota endgame tablebases (DTM, WDL). Docs.

• Probe Syzygy endgame tablebases (DTZ, WDL). Docs.

  >>> import chess.syzygy
  
  >>> tablebase = chess.syzygy.open_tablebase("data/syzygy/regular")
  
  >>> # 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")
  >>> tablebase.probe_dtz(board)
  -53
  
  >>> tablebase.close()

• Communicate with UCI/XBoard engines. Based on asyncio. Docs.

  >>> import chess.engine
  
  >>> engine = chess.engine.SimpleEngine.popen_uci("stockfish")
  
  >>> board = chess.Board("1k1r4/pp1b1R2/3q2pp/4p3/2B5/4Q3/PPP2B2/2K5 b - - 0 1")
  >>> limit = chess.engine.Limit(time=2.0)
  >>> engine.play(board, limit)  # doctest: +ELLIPSIS
  <PlayResult at ... (move=d6d1, ponder=c1d1, info={...}, draw_offered=False, resigned=False)>
  
  >>> engine.quit()

Installing

Download and install the latest release:

pip install python-chess

Selected use cases

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

• a stand-alone chess computer based on DGT board – http://www.picochess.org/
• a website to probe Syzygy endgame tablebases – https://syzygy-tables.info/
• deep learning for Crazyhouse – https://github.com/QueensGambit/CrazyAra
• a bridge between Lichess API and chess engines – https://github.com/careless25/lichess-bot
• a command-line PGN annotator – https://github.com/rpdelaney/python-chess-annotator
• an HTTP microservice to render board images – https://github.com/niklasf/web-boardimage
• a JIT compiled chess engine – https://github.com/SamRagusa/Batch-First
• a GUI to play against UCI chess engines – http://johncheetham.com/projects/jcchess/
• teaching Cognitive Science – https://jupyter.brynmawr.edu
• an Alexa skill to play blindfold chess – https://github.com/laynr/blindfold-chess
• a chessboard widget for PySide2 – https://github.com/H-a-y-k/hichesslib
• Django Rest Framework API for multiplayer chess – https://github.com/WorkShoft/capablanca-api
• a multi-agent reinforcement learning environment – https://github.com/PettingZoo-Team/PettingZoo / https://www.pettingzoo.ml/classic/chess

Acknowledgements

Thanks to the Stockfish authors and thanks to Sam Tannous for publishing his approach to avoid rotated bitboards with direct lookup (PDF) alongside his GPL2+ engine Shatranj. Some move generation ideas are taken from these sources.

Thanks to Ronald de Man for his Syzygy endgame tablebases. The probing code in python-chess is very directly ported from his C probing code.

License

python-chess is licensed under the GPL 3 (or any later version at your option). Check out LICENSE.txt for the full text.