python-chess/community

Discussing python-chess, a chess library for Python

Niklas Fiekas

@niklasf

sorry, sounds like an svglib question, tbh

in general, drawing a board directly using the gui library might be a better fit for interactive user interfaces than going via svg

NebN

@NebN

Hello, I've been reading through the docs but I can't seem to find anything regarding the customization of the "selected square" image, currently it's just a big "X", and I would like to use a custom image, is there a way to do this?

Niklas Fiekas

@niklasf

nothing like that is built in yet. you could modify the generated svg

Gandalf Sax Guy

@galacticue06

hey nicklas, how can I prevent popen_uci from creating a blank command prompt

Niklas Fiekas

@niklasf

interesting. that doesn't happen usually. which engine are you using?

Gandalf Sax Guy

@galacticue06

stockfish

stockfish 13

I tried to find subprocess.call in engine.py to add a startup flag but couldn't find

Niklas Fiekas

@niklasf

any additional keyword arguments like popen_uci(..., startupinfo=..., creationflags=...)are passed along to subprocess.Popen

Gandalf Sax Guy

@galacticue06

oh thanks

that worked

thanks a lot

Niklas Fiekas

@niklasf

still a bit strange, but glad it works like that, at least

Ghost

@ghost~58c242a5d73408ce4f4f9df5

@niklasf, what is the recommended way to manipulate the SVG data in chess.svg module? I know that the chess.svg module returns an SvgWrapper type (str type). How can I manipulate that data? Actually, how can I even pull that data out of SvgWrapper? I want to reference pieces by their id tags for drag&drop. Any examples would be very beneficial, because this isn't documented anywhere. Thanks.

Niklas Fiekas

@niklasf

it is basically really nothing but a string. so the only reliable way would be to parse it again, for example https://docs.python.org/3/library/xml.etree.elementtree.html#parsing-xml

Ghost

@ghost~58c242a5d73408ce4f4f9df5

Another question, @niklasf. When would one need the apply_transform() method of chess.Board? What purpose does it serve? Why is it there? It's not documented, so please explain.

Niklas Fiekas

@niklasf

see https://python-chess.readthedocs.io/en/latest/core.html#chess.Board.transform. it's exactly liketransform(), except that it modifies the existing board instead of creating a new one

Niklas Witzig

@nmwitzig

Hi all, I am currently trying to configure a Stockfish engine using python chess to evaluate many games. I noticed that on our university's cluster, even though I am configuring the Engine to use multiple cores using engine = chess.engine.SimpleEngine.popen_uci("/...bin/stockfish") and engine.configure({"Threads": NCPUS}), the script only uses a single core. Is there a limit on the number of threads?

Niklas Fiekas

@niklasf

@nmwitzig mhh ... no. that should definitely work. maybe the cluster has some quota?

16 replies

Ghost

@ghost~58c242a5d73408ce4f4f9df5

@niklasf, I found out that xlink:href is deprecated in favor of href, so the xlink namespace is not needed. This applies to the chess.svg module where in the <use> tags you reference chess pieces via xlink:href. Please remove the xlink namespace in the generated SVG code and fix xlink:href to just href.

Ghost

@ghost~58c242a5d73408ce4f4f9df5

I would create a pull request, but I am banned from doing so. Anyway, in svg.py, remove line 170 completely, in line 378 fix "xlink:href" to "href" and also fix "xlink:href" to "href" in line 385.

Niklas Fiekas

@niklasf

the output should be svg tiny 1.2 compatible, so deprecations from svg 2 don't apply, yet

Niklas Fiekas

@niklasf

i guess we can have both, according to https://www.w3.org/TR/SVG2/linking.html#XLinkRefAttrs

niklasf/python-chess@4f4ae6c

Ghost

@ghost~58c242a5d73408ce4f4f9df5

Very good! Thanks for the patch. This means python-chess now conforms to SVG Tiny 1.2 AND SVG 2.0 standards. That's a very welcome change.

Ghost

@ghost~58c242a5d73408ce4f4f9df5

@niklasf, please fix the alignment of white and black pawns, because their offset from the center of a square on the x axis is exactly 0.5 pixels to the left.

I have fixed this by editing the translate() data of an already generated SVG and added 0.5 pixels to the x attribute.

<use href="#white-pawn" transform="translate(15, 285)"/>
was fixed to

Ghost

@ghost~58c242a5d73408ce4f4f9df5

I don't know what exactly to fix in svg.py so that pawns (white and black) are correctly centered in the square. I don't know whether SVG path data needs to be fixed or the formula for the x and y (svg.py, lines 371 & 372).

Ghost

@ghost~58c242a5d73408ce4f4f9df5

Ghost

@ghost~58c242a5d73408ce4f4f9df5

As you can see from the screenshot image above, blue dots mark legal chess moves for the knight on f6. Notice the blue dot on the white pawn on e4. You can clearly see (well, if you look closely) that the white pawn is off center. The position of the circle is x=22.5 and y=22.5 which is the center of a square (which defaults to 45). I have monkey-patched the chess.svg.XX attribute to have this value: "<g id="xx"><circle r="5.0" cx="22.5" cy="22.5" fill="#0000ff"></circle></g>"

Ghost

@ghost~58c242a5d73408ce4f4f9df5

@niklasf, line 169 in svg.py is "version": "1.1". Shouldn't that be "version": "1.2", since the SVG documentation in the SVG rendering section says "The chess.svg module renders SVG Tiny 1.2 images"?

Niklas Fiekas

@niklasf

done via niklasf/python-chess@e7d07fd. i'll check out the pawn positions soonish

Niklas Fiekas

@niklasf

and pawns done via niklasf/python-chess@1d52ea6

Ghost

@ghost~58c242a5d73408ce4f4f9df5

Amazing work, @niklasf! Can you push a new version? Please?

Ghost

@ghost~58c242a5d73408ce4f4f9df5

The changes since v1.5.0 deserve a v1.5.1 version. Do you agree?

Also, GitHub changed the name of the 'master' branch to be named 'main' now. Can we accomodate that change?

Ghost

@ghost~58c242a5d73408ce4f4f9df5

@niklasf, thanks for v1.6.0!

Ghost

@ghost~58c242a5d73408ce4f4f9df5

@niklasf, are you willing to implement a way for us to inject JavaScript into the generated SVG? Just like there's a style argument in chess.svg.board(), it would be beneficial to have a script argument as well. If you unban me, I can make a PR.

Niklas Fiekas

@niklasf

no, but you can use an xml.etree or so to insert custom elements

Ghost

@ghost~58c242a5d73408ce4f4f9df5

I don't understand how should I even go and start manipulating your SVG document (chess.svg). I would like to add event listeners to your svg so that some drag & drop functionality can be implemented. Is that even possible? If yes, PLEASE GIVE AN EXAMPLE.

Niklas Fiekas

@niklasf

no, i told you multiple times it's not meant to do that, and this will be the last time

Ghost

@ghost~58c242a5d73408ce4f4f9df5

I have a question. Is it by design (and normal?) that a chess engine also returns its played move in the principal variation info list (i.e., in the result.info["pv"] list of chess.Move objects)? So, from the initial position of Standard Chess, if White plays 1.e4 and an engine responds with 1...e6, the result.info["pv"] list of chess.Move objects is then [chess.Move.from_uci("e7e6"), ..., ...]. Is it possible that it only outputs principal variation moves AFTER its own move in the principal variation info list (so, basically, from the pondermove onwards [hence, truncating its own played move])?

1 reply

Ghost

@ghost~58c242a5d73408ce4f4f9df5

@niklasf, there's a bug in chess.svg, namely on line 71 (CHECK_GRADIENT). The "r" attribute is missing there, so PyQt6 doesn't render the radial gradient at all and produces an error. PyQt5, for some reason, works without the "r" attribute. And as tested, adding the "r" attribute works in both frameworks. Adding the "r" attribute doesn't brake anyone's code, so it's safe to add it.

Please fix line 71 in chess.svg to be:

CHECK_GRADIENT = """<radialGradient id="check_gradient" r="0.5"><stop offset="0%" stop-color="#ff0000" stop-opacity="1.0" /><stop offset="50%" stop-color="#e70000" stop-opacity="1.0" /><stop offset="100%" stop-color="#9e0000" stop-opacity="0.0" /></radialGradient>""" # noqa: E501

2 replies

Ghost

@ghost~58c242a5d73408ce4f4f9df5

How to get the best-understandable score of a chessboard position (i.e., a centipawn score in the format like 0.41) returned by result.info["score"].white().score() (which returns a not-so-understandable value in the format like 41.00)?

Well, my approach is that I just divide the returned value of that score() method by 100. So like this: result.info["score"].white().score() / 100 (I prefer to have centipawn scores from White's point of view).

There's no mention of this "formula" (dividing by 100) in the python-chess documentation. There could (maybe even should) be a method (named perhaps centipawn_score()) that divides the returned value of that score() method by 100. It'd be used as result.info["score"].white().centipawn_score() to get the actual (centipawn) score (like 0.41, as it is displayed by all chess GUIs I know) and not a (perhaps strange) number (like 41.00).

Can this be implemented?

Ghost

@ghost~58c242a5d73408ce4f4f9df5

I would fix the method score() of the Cp class in chess.engine on line 644 and define it like this:

def score(self, *, mate_score: Optional[int] = None) -> float:
    return self.cp / 100

Ghost

@ghost~58c242a5d73408ce4f4f9df5

@niklasf, I think it would be more reasonable for the find_move() method of chess.Board() to return None if no legal move is found by it. It now raises a ValueError exception, but I think that could be improved. It's better to do if board.find_move(some_move) is not None than to have a try/except block.

Sam Q

@SamQ26867433_twitter

Hi, I'd like to know how to change the colors of the light and dark chessboard squares. An example would be nice.

Sam Q

@SamQ26867433_twitter

I know I can go to the svg.py file and change the light and dark colors there, but I'd like to know how do do it without modifying the python-chess library.

Ghost

@ghost~58c242a5d73408ce4f4f9df5

@SamQ26867433_twitter, the way I do it is like this:

firstly, I define a Python dictionary and override those default python-chess hex values that represent colors

my_default_theme = {
 "coord": "#f0f6fd80",
 "margin": "#15781b80",
 "arrow red": "#88202080",
 "arrow blue": "#00308880",
 "arrow green": "#15781b80",
 "square dark": "#e5e5e5ff",
 "square light": "#f0f6fdff",
 "arrow yellow": "#e68f0080",
 "square dark lastmove": "#8b000080",
 "square light lastmove": "#8b000080",
}

then I just pass this my_default_theme dictionary to chess.svg.board(..., colors=my_default_theme)

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