国际象棋 GUI 应用程序未收到使用通用国际象棋接口 (UCI) 的国际象棋引擎的响应

Question

I've coded some toy chess engines in the past using different languages, all of them providing their own simple text-based UI. Now I want to write an engine that can be used with chess GUIs like ChessX or Cute Chess. I've read and understood (at least I thought so) the Universal Chess Interface (UCI) protocol.

To get a first working version, I'm using Python (3.9 on macOS) for my engine, here's the part that's looking for input via STDIN a full (non-)working example as requested:

import sys
import os
import time
import re
import select
import fileinput


if __name__ == '__main__':
    while True:
        if select.select([sys.stdin, ], [], [], 0.0)[0]:
            for line in fileinput.input():
                tokens = [ x.strip().lower() for x in re.split("\s+", line.strip()) ]
                if tokens[0] == "uci":
                    sys.stdout.write("id name mychess\n")
                    sys.stdout.write("id author myname\n")
                    sys.stdout.write("uciok\n")
                elif tokens[0] == "isready":
                    sys.stdout.write("readyok\n")
        time.sleep(2)

When I put my engine in one of the GUIs (or a simple python-chess app, see below), my engine gets the initial "uci" command and answers accordingly as I can verify using some test and logging code not shown in the minimal example above.

But then, nothing happens ... until the GUIs are telling me they timed-out. Obviously, they didn't get any answer from my engine. Using the python-chess library, I can verify that the response from my engine isn't coming through to the GUI process.

This is the code in my python-chess app to connect to my engine:

engine = chess.engine.SimpleEngine.popen_uci(r"./engine.py")

If I put there the path to the stockfish engine, I can see the response from that engine and how the python-chess app answers with "ucinewgame" and a lot of other communication.

So, why is the response from my engine not read by the GUI client?

Update: I suspect it has something to do with the select code in my example. It's there to simulate non-blocking access to STDIN. In a simpler approach, I'm just using a blocking call to input and it works (here's the gist of it):

while True:
    line = input()
    if line.strip().lower() == "uci":
        print("id name mychess")
        print("uciok")

Answer 1

The problem seems to be in using select.select() and/or fileinput.input() . If I omit those fancy techniques and simply read from STDIN, everything works and cutechess accepts my engine. This is the basic code for a UCI chess engine to get recognized:

import sys
import os
import re


if __name__ == '__main__':
    while True:
        line = input()
        tokens = [ x.strip().lower() for x in re.split("\s+", line.strip()) ]
        if tokens[0] == "uci":
            sys.stdout.write("id name mychess\n")
            sys.stdout.write("id author myname\n")
            sys.stdout.write("uciok\n")
        elif tokens[0] == "isready":
            print("readyok")

Of course, the blocking call to input() now doesn't allow for concurrent calculations in my engine while accepting input from the GUI immediately, but that's stuff for perhaps another question.