Stockfish: Giving illegal FEN to stockfish doesn't raise Exception.

[rayoh123]

For example, why doesn't the below code with an illegal FEN raise an exception? The code below DOESN'T print Oops like it should. How can I get Stockfish to raise an exception when an illegal FEN is given?

import chess
import chess.engine

engine = chess.engine.SimpleEngine.popen_uci("stockfish_10_x64.exe")
try:
    with engine.analysis(chess.Board('5rk1/ppp2pbp/3pk1p1/1q6/4r1P1/1nPrBB2/PP2nPP1/R2QR2K')) as analysis:
        for info in analysis:
            print(info.get("score"), info.get("pv"))

            # Unusual stop condition.
            if info.get("hashfull", 0) > 50:
                break
except:
    print("oops")
engine.quit()

[ddugovic]

The UCI specification does not specify how to handle invalid input.

[rayoh123]

The UCI specification does not specify how to handle invalid input.

So there is no way to catch an illegal FEN?

[ddugovic]

905 and #1978 are the same issue; any solution would degrade performance and complicate testing.

[MichaelB7]

GUIs should be able to catch, and in some cases correct bad FENS , at the command line the user should ensure the FEN is correct. I know xBoard can correct some faulty FENs. The behavior to exit is correct since that is a signal to the user at the command line that the FEN is improper.

[niklasf]

@rayoh123 Note that python-chess did the following:

>>> import chess
>>> chess.Board("5rk1/ppp2pbp/3pk1p1/1q6/4r1P1/1nPrBB2/PP2nPP1/R2QR2K")
Board('5rk1/ppp2pbp/3pk1p1/1q6/4r1P1/1nPrBB2/PP2nPP1/R2QR2K w - - 0 1')

Also it's very unlikely that you really want the silly stop condition (which was just an example in the python-chess documentation):

            # Unusual stop condition.
            if info.get("hashfull", 0) > 50:
                break