Board.__str__ including grid labels

[jamesbraza]

To me, it's easier to see/understand a board's printed representation with the rank/file shown.

In [1]: import chess
In [2]: board = chess.Board()
In [3]: print(board)
r n b q k b n r
p p p p p p p p
. . . . . . . .
. . . . . . . .
. . . . . . . .
. . . . . . . .
P P P P P P P P
R N B Q K B N R

It would be nice to support the ability to show the grid:

In [4]: print(board.grid())
  | a b c d e f g h
- + ---------------
8 | r n b q k b n r
7 | p p p p p p p p
6 | . . . . . . . .
5 | . . . . . . . .
4 | . . . . . . . .
3 | . . . . . . . .
2 | P P P P P P P P
1 | R N B Q K B N R

Alternately, an instance attribute verbose could be added that somehow enables behaviors like this when __str__ is invoked.

[niklasf]

I think this looks good. I wonder if it's acceptable to just change __str__, or if that would be considered a breaking change.

[jamesbraza]

Yeah I think it would be fine to change __str__ too.

One question is, how do you see board.mirror() affecting things?

[niklasf]

One question is, how do you see board.mirror() affecting things?

board.mirror() should not need special consideration. It's not to be confused with changing the orientation of looking at the board - chess.Board() has no concept of that. board.mirror() returns a different position, that happens to have pieces in mirrored positions.

[dubiousjim]

For reference, here is a prettifying wrapper I use around str(Board):

def diagram(b, *, flipped=False, labels=0, pretty=False):
    # pylint: disable=multiple-statements,consider-using-f-string
    assert isinstance(b, Board), f"Not a Board: {repr(b)}"
    string = b.unicode(empty_square='.') if pretty else str(b)
    if flipped:
        rows = [''.join(reversed(row)) for row in reversed(string.split('\n'))]
        if labels == 0: return '\n'.join(rows)
        elif labels == 1: return '\n'.join('%d %s' % (i,row) for i,row in enumerate(rows, start=1)) + '\n  h g f e d c b a'
        elif labels == -1: return '  h g f e d c b a\n' + '\n'.join('  %s %d' % (row,i) for i,row in enumerate(rows, start=1))
        else: return '    h g f e d c b a\n  + --------------- +\n' + '\n'.join('%d | %s | %d' % (i,row,i) for i,row in enumerate(rows, start=1)) + '\n  + --------------- +\n    h g f e d c b a'
    else:
        rows = string.split('\n')
        if labels == 0: return '\n'.join(rows)
        # pylint: disable=consider-using-in
        elif labels == 1 or labels == -1: return '\n'.join('%d %s' % (8-i,row) for i,row in enumerate(rows)) + '\n  a b c d e f g h'
        else: return '    a b c d e f g h\n  + --------------- +\n' + '\n'.join('%d | %s | %d' % (8-i,row,8-i) for i,row in enumerate(rows)) + '\n  + --------------- +\n    a b c d e f g h'

[dubiousjim]

Use pretty=True to get Unicode pieces. Use flipped=True to invert the perspective (putting black on bottom). Use labels=1 to get row/column labels to the left and bottom of the board. When flipped=True, you can also use labels=-1 to get labels on the top and right of the board instead. (When flipped=False, labels=-1 works just like labels=1.)

No grid lines. But this is a starting point that someone can use to write something more full-featured.

[jamesbraza]

@dubiousjim I like your support of unicode, nice! I am using this now 👍, with a few mods:

• I changed labels arg name to verbosity and only support [0, 1, 2]
• I moved from "\n" to os.linesep
• From this comment above:

board.mirror() should not need special consideration.

I think this means no need to support flipped capability, just rely on the caller previously invoking board.apply_mirror() or board.mirror().

One possible improvement for labels/verbosity=2: maybe add the player whose turn it is with * or . as the corner. This can be discerned with board.turn == chess.WHITE and board.turn == chess.BLACK.

For example, if it's white player's turn, note the *:

    a b c d e f g h
  . --------------- .
8 | r . b q k b . r | 8
7 | p p . n p p . p | 7
6 | . . p p . n p . | 6
5 | . . . . . . . . | 5
4 | . . . . P . . . | 4
3 | . . N . . N . P | 3
2 | P P P P B P P . | 2
1 | R . B Q K . . R | 1
  * --------------- *
    a b c d e f g h

[dubiousjim]

Flipped board just displays the 8 rank at the bottom, it doesn't change any piece positions. (White K still starts at e1, this is just now displayed at the top instead of at the bottom.) Mirrored board moves the piece that was at a6 instead to a3. These are different concepts.

[jamesbraza]

Okay I see, sorry I didn't scrutinize that much. I think the default chess behavior is 8th rank on the top.

One other cool feature in a display function would be to highlight captures, check, or checkmates, possibly via colors. This behavior could be turned on with an additional color flag.

[baelany]

I would be interested in taking on this issue!

[R3dan]

I would also be interested in taking this, if someone already is in development though, please say

[Phillyclause89]

What is Board had a Board.__format__(format_spec) method? Then we could keep the default print behavior unchanged for any consumer that may be using that out there as well as support something like print(f"{board:grid_labels}") ?

https://peps.python.org/pep-3101/#controlling-formatting-on-a-per-type-basis

[dubiousjim]

Sounds great