CODEWITHSUNDEEP
python-chess
user3179236
user3179236

Reputation: 49

What is the best way to find out if the move captured a piece in python chess?

The best way I found to check if the move captured a piece is to count all the pieces before and after the move and verify if different, but seems to me very inefficient and not elegant.

Upvotes: 1

Views: 2762

Answers (3)

Jackson H
Jackson H

Reputation: 192

Board's is_capture method encapsulates the necessary logic for normal captures as well as en passant:

# Position after e4 d5
b = chess.Board('rnbqkbnr/ppp1pppp/8/3p4/4P3/8/PPPP1PPP/RNBQKBNR w KQkq - 0 1')
move = chess.Move.from_uci('e4d5')
print(b.is_capture(move))  # True

Here is how they actually implement it (copied directly from Board):

def is_capture(self, move: Move) -> bool:
    """Checks if the given pseudo-legal move is a capture."""
    touched = BB_SQUARES[move.from_square] ^ BB_SQUARES[move.to_square]
    return bool(touched & self.occupied_co[not self.turn]) or self.is_en_passant(move)

Upvotes: 1

narkfestmojo
narkfestmojo

Reputation: 21

You also need to check for en passant, but I think that is all you have to worry about.

The following code should work; it returns 0 if nothing captured, otherwise uses the codes from python chess (e.g. chess.PAWN, chess.ROOK, etc.):

def CapturedPiece(board, move):
    if board.is_capture(move):
        if board.is_en_passant(move):
            return chess.PAWN
        else:
            return board.piece_at(move.to_square).piece_type
    return 0

I couldn't find a function in the module that does this already, but that doesn't mean it doesn't exist or that it won't be added at some point.

Upvotes: 2

user3179236
user3179236

Reputation: 49

I've found a better way than counting (even if still not nice is the best so far).

Verify if in the target square there is a piece or if the move is of a pawn verify if source and target file (x coordinate) is different.

quiet = board.piece_type_at(move.to_square)==None
if ( board.piece_type_at(move.from_square)==chess.PAWN ) \
   and ( chess.square_file(move.from_square)!=chess.square_file(move.to_square) ):
    quiet=False

Upvotes: 0

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