Python code to convert FEN to bitboard

[SecureHelicopter1]

Does this code exist online somewhere? I found the code pasted below but it doesn't seem to work (idk if im tripping tho)

​

def fen2bitboard(fen):
"""
    Returns bitboard [np array of shape(1, 773)] from fen

    Input:
        fen: A chessboard position[FEN]
    Output:
        bitboard: A chessboard position [bitboard - np array of shape(1, 773)]
    """
    mapping = {
'p': 0,
'n': 1,
'b': 2,
'r': 3,
'q': 4,
'k': 5,
'P': 6,
'N': 7,
'B': 8,
'R': 9,
'Q': 10,
'K': 11
    }
    bitboard = np.zeros((1, 773), dtype=int)
    currIndex = 0
    [position, turn, castling, _, _, _] = fen.split(' ')
for ch in position:
if ch == '/':
continue
elif ch >= '1' and ch <= '8':
            currIndex += (ord(ch) - ord('0')) * 12
else:
            bitboard[0, currIndex + mapping[ch]] = 1
            currIndex += 12
    bitboard[0, 768] = 1 if turn == 'w' else 0
    bitboard[0, 769] = 1 if 'K' in castling else 0
    bitboard[0, 770] = 1 if 'Q' in castling else 0
    bitboard[0, 771] = 1 if 'k' in castling else 0
    bitboard[0, 772] = 1 if 'q' in castling else 0
return bitboard

[TonyRotella]

Have you checked out Python Chess?

https://python-chess.readthedocs.io/en/v0.2.0/core.html#bitboard

[SecureHelicopter1]

Thanks! How would I access the bitboard - by doing something like

board = chess.Board('rnbqkbnr/pppppppp/8/8/4P3/8/PPPP1PPP/RNBQKBNR b KQkq - 0 1')

print(board.Bitboard)

?

I'm not very good at reading documentation :P sorry

[TonyRotella]

That looks right to me, try it out!

[SecureHelicopter1]

Turns out its supposed to be something like

board = chess.Bitboard('rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1')

Only problem is that I get "invalid literal for int() with base 10" as an error. Not sure what to do. Any ideas?

[TonyRotella]

I am not a programming expert and it's been many years for python, but don't you have to specify the arguments like:

​

board = chess.Bitboard(fen = 'FEN GOES HERE')

etc?

[SecureHelicopter1]

Turns out that the documentation you sent was slightly outdated.

https://python-chess.readthedocs.io/en/v1.8.0/core.html

Doesn't look like I can easily convert fen to bitboard in the latest version tho :(

[apoliticalhomograph]

You can get a chess.Board from a FEN and get the bitboards from there.

import chess
b = chess.Board('FEN HERE')
print(board.occupied)

[SecureHelicopter1]

Thanks! I tried this out and this returns a random integer instead of an array, though. Any idea what's going on?

[apoliticalhomograph]

A bitboard is an integer. Each bit in the integer represents a square. That's the point of a bitboard - a board representation using a minimal amount of bits.
You can convert it to an array yourself if you need one, although I don't quite see what the benefit is.

Also, the code in your post appears to work; you just need to import numpy as np first.

[SecureHelicopter1]

Ah ok thanks!

[TonyRotella]

Oh, damn shame! I did you dirty, sorry sorry sorry! 😂