How to efficiently get material balance

[pavolkacej]

How can I get the difference of material at current position? Like if white is down a rook, the result will be -5.
Is there a fancy efficient way to do it (for example using bitwise operation), or do I have to implement it myself?

[niklasf]

The most efficient bitboard-based implementation is a bit verbose:

import chess

def material_balance(board):
    white = board.occupied_co[chess.WHITE]
    black = board.occupied_co[chess.BLACK]
    return (
        chess.popcount(white & board.pawns) - chess.popcount(black & board.pawns) +
        3 * (chess.popcount(white & board.knights) - chess.popcount(black & board.knights)) +
        3 * (chess.popcount(white & board.bishops) - chess.popcount(black & board.bishops)) +
        5 * (chess.popcount(white & board.rooks) - chess.popcount(black & board.rooks)) +
        9 * (chess.popcount(white & board.queens) - chess.popcount(black & board.queens))
    )

Chess engines usually maintain an incrementally updated balance.

[jacksonthall22]

a bit verbose

nice one :)