python-chess: a pure Python chess library

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

Documentation

https://python-chess.readthedocs.org/en/latest/

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'))
  
  >>> # 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 futures # Backport for Python < 3.2
  sudo pip install python-chess
  

• From current source code:

  python setup.py sdist
  sudo python setup.py install
  

Featured projects

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

• a stand alone chess computer based on DGT board - http://www.picochess.org/
• a cross platform chess GUI - https://asdfjkl.github.io/jerry/
• a website to probe Syzygy endgame tablebases - https://syzygy-tables.info/
• extracting reasoning from chess engines - https://github.com/pcattori/deep-blue-talks

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.