UCI/XBoard engine communication

UCI and XBoard are protocols for communicating with chess engines. This module implements an abstraction for playing moves and analysing positions with both kinds of engines.

The preferred way to use the API is with an asyncio event loop. The examples also show a synchronous wrapper SimpleEngine that automatically spawns an event loop in the background.

Playing

Example: Let Stockfish play against itself, 100 milliseconds per move.

import chess
import chess.engine

engine = chess.engine.SimpleEngine.popen_uci("/usr/bin/stockfish")

board = chess.Board()
while not board.is_game_over():
    result = engine.play(board, chess.engine.Limit(time=0.100))
    board.push(result.move)

engine.quit()
import asyncio
import chess
import chess.engine

async def main():
    transport, engine = await chess.engine.popen_uci("/usr/bin/stockfish")

    board = chess.Board()
    while not board.is_game_over():
        result = await engine.play(board, chess.engine.Limit(time=0.100))
        board.push(result.move)

    await engine.quit()

asyncio.set_event_loop_policy(chess.engine.EventLoopPolicy())
asyncio.run(main())
class chess.engine.EngineProtocol(*, loop=None)[source]

Protocol for communicating with a chess engine process.

coroutine play(board: chess.Board, limit: chess.engine.Limit, *, game: object = None, info: chess.engine.Info = <Info.NONE: 0>, ponder: bool = False, root_moves: Optional[Iterable[chess.Move]] = None, options: Mapping[str, Union[str, int, bool, None]] = {}) → chess.engine.PlayResult[source]

Play a position.

Parameters:
  • board – The position. The entire move stack will be sent to the engine.
  • limit – An instance of chess.engine.Limit that determines when to stop thinking.
  • game – Optional. An arbitrary object that identifies the game. Will automatically inform the engine if the object is not equal to the previous game (e.g. ucinewgame, new).
  • info – Selects which additional information to retrieve from the engine. INFO_NONE, INFO_BASE (basic information that is trivial to obtain), INFO_SCORE, INFO_PV, INFO_REFUTATION, INFO_CURRLINE, INFO_ALL or any bitwise combination. Some overhead is associated with parsing extra information.
  • ponder – Whether the engine should keep analysing in the background even after the result has been returned.
  • root_moves – Optional. Consider only root moves from this list.
  • options – Optional. A dictionary of engine options for the analysis. The previous configuration will be restored after the analysis is complete. You can permanently apply a configuration with configure().
class chess.engine.Limit(*, time: Optional[float] = None, depth: Optional[int] = None, nodes: Optional[int] = None, mate: Optional[int] = None, white_clock: Optional[float] = None, black_clock: Optional[float] = None, white_inc: Optional[float] = None, black_inc: Optional[float] = None, remaining_moves: Optional[int] = None)[source]

Search termination condition.

time

Search exactly time seconds.

depth

Search depth ply only.

nodes

Search only a limited number of nodes.

mate

Search for a mate in mate moves.

white_clock

Time in seconds remaining for White.

black_clock

Time in seconds remaining for Black.

white_inc

Fisher increment for White, in seconds.

black_inc

Fisher increment for Black, in seconds.

remaining_moves

Number of moves to the next time control. If this is not set, but white_clock and black_clock are, then it is sudden death.

class chess.engine.PlayResult(move: Optional[chess.Move], ponder: Optional[chess.Move], info: Optional[chess.engine.InfoDict] = None, *, draw_offered: bool = False, resigned: bool = False)[source]

Returned by chess.engine.EngineProtocol.play().

move

The best move accordig to the engine, or None.

ponder

The response that the engine expects after move, or None.

info

A dictionary of extra information sent by the engine. Commonly used keys are: score (a PovScore), pv (a list of Move objects), depth, seldepth, time (in seconds), nodes, nps, tbhits, multipv.

Others: currmove, currmovenumber, hashfull, cpuload, refutation, currline, ebf and string.

draw_offered

Whether the engine offered a draw before moving.

resigned

Whether the engine resigned.

Analysing and evaluating a position

Example:

import chess
import chess.engine

engine = chess.engine.SimpleEngine.popen_uci("/usr/bin/stockfish")

board = chess.Board()
info = engine.analyse(board, chess.engine.Limit(time=0.100))
print("Score:", info["score"])
# Score: +20

board = chess.Board("r1bqkbnr/p1pp1ppp/1pn5/4p3/2B1P3/5Q2/PPPP1PPP/RNB1K1NR w KQkq - 2 4")
info = engine.analyse(board, chess.engine.Limit(depth=20))
print("Score:", info["score"])
# Score: #1

engine.quit()
import asyncio
import chess
import chess.engine

async def main():
    transport, engine = await chess.engine.popen_uci("/usr/bin/stockfish")

    board = chess.Board()
    info = await engine.analyse(board, chess.engine.Limit(time=0.100))
    print(info["score"])
    # Score: +20

    board = chess.Board("r1bqkbnr/p1pp1ppp/1pn5/4p3/2B1P3/5Q2/PPPP1PPP/RNB1K1NR w KQkq - 2 4")
    info = await engine.analyse(board, chess.engine.Limit(depth=20))
    print(info["score"])
    # Score: #1

    await engine.quit()

asyncio.set_event_loop_policy(chess.engine.EventLoopPolicy())
asyncio.run(main())
class chess.engine.EngineProtocol(*, loop=None)[source]

Protocol for communicating with a chess engine process.

coroutine analyse(board: chess.Board, limit: chess.engine.Limit, *, multipv: Optional[int] = None, game: object = None, info: chess.engine.Info = <Info.ALL: 31>, root_moves: Optional[Iterable[chess.Move]] = None, options: Mapping[str, Union[str, int, bool, None]] = {}) → Union[List[chess.engine.InfoDict], chess.engine.InfoDict][source]

Analyses a position and returns a dictionary of information.

Parameters:
  • board – The position to analyse. The entire move stack will be sent to the engine.
  • limit – An instance of chess.engine.Limit that determines when to stop the analysis.
  • multipv – Optional. Analyse multiple root moves. Will return a list of at most multipv dictionaries rather than just a single info dictionary.
  • game – Optional. An arbitrary object that identifies the game. Will automatically inform the engine if the object is not equal to the previous game (e.g. ucinewgame, new).
  • info – Selects which information to retrieve from the engine. INFO_NONE, INFO_BASE (basic information that is trivial to obtain), INFO_SCORE, INFO_PV, INFO_REFUTATION, INFO_CURRLINE, INFO_ALL or any bitwise combination. Some overhead is associated with parsing extra information.
  • root_moves – Optional. Limit analysis to a list of root moves.
  • options – Optional. A dictionary of engine options for the analysis. The previous configuration will be restored after the analysis is complete. You can permanently apply a configuration with configure().
class chess.engine.PovScore(relative: chess.engine.Score, turn: bool)[source]

A relative Score and the point of view.

relative

The relative Score.

turn

The point of view (chess.WHITE or chess.BLACK).

white() → chess.engine.Score[source]

Get the score from White’s point of view.

black() → chess.engine.Score[source]

Get the score from Black’s point of view.

pov(color: bool) → chess.engine.Score[source]

Get the score from the point of view of the given color.

is_mate() → bool[source]

Tests if this is a mate score.

class chess.engine.Score[source]

Evaluation of a position.

The score can be Cp (centi-pawns), Mate or MateGiven. A positive value indicates an advantage.

There is a total order defined on centi-pawn and mate scores.

>>> from chess.engine import Cp, Mate, MateGiven
>>>
>>> Mate(-0) < Mate(-1) < Cp(-50) < Cp(200) < Mate(4) < Mate(1) < MateGiven
True

Scores can be negated to change the point of view:

>>> -Cp(20)
Cp(-20)
>>> -Mate(-4)
Mate(+4)
>>> -Mate(0)
MateGiven
score(*, mate_score: Optional[int] = None) → Optional[int][source]

Returns the centi-pawn score as an integer or None.

You can optionally pass a large value to convert mate scores to centi-pawn scores.

>>> Cp(-300).score()
-300
>>> Mate(5).score() is None
True
>>> Mate(5).score(mate_score=100000)
99995
mate() → Optional[int][source]

Returns the number of plies to mate, negative if we are getting mated, or None.

Warning:This conflates Mate(0) (we lost) and MateGiven (we won) to 0.
is_mate() → bool[source]

Tests if this is a mate score.

Indefinite or infinite analysis

Example: Stream information from the engine and stop on an arbitrary condition.

import chess
import chess.engine

engine = chess.engine.SimpleEngine.popen_uci("/usr/bin/stockfish")

with engine.analysis(chess.Board()) as analysis:
    for info in analysis:
        print(info.get("score"), info.get("pv"))

        # Unusual stop condition.
        if info.get("hashfull", 0) > 900:
            break

engine.quit()
import asyncio
import chess
import chess.engine

async def main():
    transport, engine = await chess.engine.popen_uci("/usr/bin/stockfish")

    with await engine.analysis(chess.Board()) as analysis:
        async for info in analysis:
            print(info.get("score"), info.get("pv"))

            # Unusual stop condition.
            if info.get("hashfull", 0) > 900:
                break

    await engine.quit()

asyncio.set_event_loop_policy(chess.engine.EventLoopPolicy())
asyncio.run(main())
class chess.engine.EngineProtocol(*, loop=None)[source]

Protocol for communicating with a chess engine process.

coroutine analysis(board: chess.Board, limit: Optional[chess.engine.Limit] = None, *, multipv: Optional[int] = None, game: object = None, info: chess.engine.Info = <Info.ALL: 31>, root_moves: Optional[Iterable[chess.Move]] = None, options: Mapping[str, Union[str, int, bool, None]] = {}) → chess.engine.AnalysisResult[source]

Starts analysing a position.

Parameters:
  • board – The position to analyse. The entire move stack will be sent to the engine.
  • limit – Optional. An instance of chess.engine.Limit that determines when to stop the analysis. Analysis is infinite by default.
  • multipv – Optional. Analyse multiple root moves.
  • game – Optional. An arbitrary object that identifies the game. Will automatically inform the engine if the object is not equal to the previous game (e.g. ucinewgame, new).
  • info – Selects which information to retrieve from the engine. INFO_NONE, INFO_BASE (basic information that is trivial to obtain), INFO_SCORE, INFO_PV, INFO_REFUTATION, INFO_CURRLINE, INFO_ALL or any bitwise combination. Some overhead is associated with parsing extra information.
  • root_moves – Optional. Limit analysis to a list of root moves.
  • options – Optional. A dictionary of engine options for the analysis. The previous configuration will be restored after the analysis is complete. You can permanently apply a configuration with configure().

Returns AnalysisResult, a handle that allows asynchronously iterating over the information sent by the engine and stopping the the analysis at any time.

class chess.engine.AnalysisResult(stop: Optional[Callable[[], None]] = None)[source]

Handle to ongoing engine analysis. Returned by chess.engine.EngineProtocol.analysis().

Can be used to asynchronously iterate over information sent by the engine.

Automatically stops the analysis when used as a context manager.

info

A dictionary of aggregated information sent by the engine. This is actually an alias for multipv[0].

multipv

A list of dictionaries with aggregated information sent by the engine. One item for each root move.

stop() → None[source]

Stops the analysis as soon as possible.

empty() → bool[source]

Checks if all information has been consumed.

If the queue is empty, but the analysis is still ongoing, then further information can become available in the future.

If the queue is not empty, then the next call to get() will return instantly.

coroutine get() → chess.engine.InfoDict[source]

Waits for the next dictionary of information from the engine and returns it.

It might be more convenient to use async for info in analysis: ....

Raises:chess.engine.AnalysisComplete if the analysis is complete (or has been stopped) and all information has been consumed. Use next() if you prefer to get None instead of an exception.
coroutine wait() → None[source]

Waits until the analysis is complete (or stopped).

Options

configure(), play(), analyse() and analysis() accept a dictionary of options.

>>> import chess.engine
>>>
>>> engine = chess.engine.SimpleEngine.popen_uci("/usr/bin/stockfish")
>>>
>>> # Check available options.
>>> engine.options["Hash"]
Option(name='Hash', type='spin', default=16, min=1, max=131072, var=[])
>>>
>>> # Set an option.
>>> engine.configure({"Hash": 32})
>>>
>>> # [...]
import asyncio
import chess.engine

async def main():
    transport, protocol = await chess.engine.popen_uci("/usr/bin/stockfish")

    # Check available options.
    print(engine.options["Hash"])
    # Option(name='Hash', type='spin', default=16, min=1, max=131072, var=[])

    # Set an option.
    await engine.configure({"Hash": 32})

    # [...]

asyncio.set_event_loop_policy(chess.engine.EventLoopPolicy())
asyncio.run(main())
class chess.engine.EngineProtocol(*, loop=None)[source]

Protocol for communicating with a chess engine process.

options

Dictionary of available options.

coroutine configure(options: Mapping[str, Union[str, int, bool, None]]) → None[source]

Configures global engine options.

Parameters:options – A dictionary of engine options, where the keys are names of options. Do not set options that are managed automatically (chess.engine.Option.is_managed()).
class chess.engine.Option[source]

Information about an available engine option.

name

The name of the option.

type

The type of the option.

type UCI CECP value
check X X True or False
button X X None
reset   X None
save   X None
string X X string without line breaks
file   X string, interpreted as the path to a file
path   X string, interpreted as the path to a directory
default

The default value of the option.

min

The minimum integer value of a spin option.

max

The maximum integer value of a spin option.

var

A list of allowed string values for a combo option.

is_managed() → bool[source]

Some options are managed automatically: UCI_Chess960, UCI_Variant, UCI_AnalyseMode, MultiPV, Ponder.

Logging

Communication is logged with debug level on a logger named chess.engine. Debug logs are useful while troubleshooting. Please also provide them when submitting bug reports.

import logging

# Enable debug logging.
logging.basicConfig(level=logging.DEBUG)

AsyncSSH

EngineProtocol can also be used with AsyncSSH (since 1.16.0) to communicate with an engine on a remote computer.

import asyncio
import asyncssh
import chess
import chess.engine

async def main():
    async with asyncssh.connect("localhost") as conn:
        channel, engine = await conn.create_subprocess(chess.engine.UciProtocol, "/usr/bin/stockfish")
        await engine.initialize()

        # Play, analyse, ...
        await engine.ping()

asyncio.run(main())

Reference

class chess.engine.EngineError[source]

Runtime error caused by a misbehaving engine or incorrect usage.

class chess.engine.EngineTerminatedError[source]

The engine process exited unexpectedly.

class chess.engine.AnalysisComplete[source]

Raised when analysis is complete, all information has been consumed, but further information was requested.

coroutine chess.engine.popen_uci(command: Union[str, List[str]], *, setpgrp: bool = False, loop=None, **popen_args) → Tuple[asyncio.transports.SubprocessTransport, chess.engine.UciProtocol][source]

Spawns and initializes an UCI engine.

Parameters:
  • command – Path of the engine executable, or a list including the path and arguments.
  • setpgrp – Open the engine process in a new process group. This will stop signals (such as keyboard interrupts) from propagating from the parent process. Defaults to False.
  • popen_args – Additional arguments for popen. Do not set stdin, stdout, bufsize or universal_newlines.

Returns a subprocess transport and engine protocol pair.

coroutine chess.engine.popen_xboard(command: Union[str, List[str]], *, setpgrp: bool = False, **popen_args) → Tuple[asyncio.transports.SubprocessTransport, chess.engine.XBoardProtocol][source]

Spawns and initializes an XBoard engine.

Parameters:
  • command – Path of the engine executable, or a list including the path and arguments.
  • setpgrp – Open the engine process in a new process group. This will stop signals (such as keyboard interrupts) from propagating from the parent process. Defaults to False.
  • popen_args

    Additional arguments for popen. Do not set stdin, stdout, bufsize or universal_newlines.

Returns a subprocess transport and engine protocol pair.

class chess.engine.EngineProtocol(*, loop=None)[source]

Protocol for communicating with a chess engine process.

returncode

Future: Exit code of the process.

id

Dictionary of information about the engine. Common keys are name and author.

coroutine initialize() → None[source]

Initializes the engine.

coroutine ping() → None[source]

Pings the engine and waits for a response. Used to ensure the engine is still alive and idle.

coroutine quit() → None[source]

Asks the engine to shut down.

class chess.engine.UciProtocol[source]

An implementation of the Universal Chess Interface protocol.

class chess.engine.XBoardProtocol[source]

An implementation of the XBoard protocol (CECP).

class chess.engine.SimpleEngine(transport: asyncio.transports.SubprocessTransport, protocol: chess.engine.EngineProtocol, *, timeout: Optional[float] = 10.0)[source]

Synchronous wrapper around a transport and engine protocol pair. Provides the same methods and attributes as EngineProtocol, with blocking functions instead of coroutines.

You may not concurrently modify objects passed to any of the methods. Other than that SimpleEngine is thread-safe. When sending a new command to the engine, any previous running command will be cancelled as soon as possible.

Methods will raise asyncio.TimeoutError if an operation takes timeout seconds longer than expected (unless timeout is None).

Automatically closes the transport when used as a context manager.

close() → None[source]

Closes the transport and the background event loop as soon as possible.

classmethod popen_uci(command: Union[str, List[str]], *, timeout: Optional[float] = 10.0, debug: bool = False, setpgrp: bool = False, **popen_args) → chess.engine.SimpleEngine[source]

Spawns and initializes an UCI engine. Returns a SimpleEngine instance.

classmethod popen_xboard(command: Union[str, List[str]], *, timeout: Optional[float] = 10.0, debug: bool = False, setpgrp: bool = False, **popen_args) → chess.engine.SimpleEngine[source]

Spawns and initializes an XBoard engine. Returns a SimpleEngine instance.

class chess.engine.SimpleAnalysisResult(simple_engine: chess.engine.SimpleEngine, inner: chess.engine.AnalysisResult)[source]

Synchronous wrapper around AnalysisResult. Returned by chess.engine.SimpleEngine.analysis().

chess.engine.EventLoopPolicy() → None[source]

An event loop policy that ensures the event loop is capable of spawning and watching subprocesses, even when not running in the main thread.

Windows: Creates a ProactorEventLoop.

Unix: Creates a SelectorEventLoop. Child watchers are thread local. When not running on the main thread, the default child watchers use relatively slow polling to detect process termination. This does not affect communication.