def heur(board: ChessState) -> int:
"""Evaluation function for a given ChessState. The upper- and lower-bounds for the value returned are
10000 and -10000. A value of 0 indicates an equal position."""
if board.is_checkmate():
if board.turn:
#black won
return -10000
else:
#white won
return 10000
elif board.is_stalemate() or board.is_insufficient_material():
return 0
#get piece positions
white_pawns = board.pieces(chess.PAWN, chess.WHITE)
black_pawns = board.pieces(chess.PAWN, chess.BLACK)
white_knights = board.pieces(chess.KNIGHT, chess.WHITE)
black_knights = board.pieces(chess.KNIGHT, chess.BLACK)
white_bishops = board.pieces(chess.BISHOP, chess.WHITE)
black_bishops = board.pieces(chess.BISHOP, chess.BLACK)
white_rooks = board.pieces(chess.ROOK, chess.WHITE)
black_rooks = board.pieces(chess.ROOK, chess.BLACK)
white_queens = board.pieces(chess.QUEEN, chess.WHITE)
black_queens = board.pieces(chess.QUEEN, chess.BLACK)
white_king = board.pieces(chess.KING, chess.WHITE)
black_king = board.pieces(chess.KING, chess.BLACK)
num_of_pieces = len(black_knights) + len(black_bishops) + len(black_rooks) +\
len(white_knights) + len(white_bishops) + len(white_rooks) + len(white_queens) \
+ len(black_queens) + len(white_king) + len(black_king) + len(white_pawns) + len(black_pawns)
#returns number of pinned pieces from piece_set * value_of_pin
def pinned_eval(piece_set, color, value_of_pin):
cum_eval = 0
for piece in piece_set:
if board.is_pinned(color, piece):
cum_eval = cum_eval + value_of_pin
return cum_eval
pinned_value = pinned_eval(white_pawns, chess.WHITE, -20) + pinned_eval(black_pawns, chess.BLACK, 20) + \
pinned_eval(white_knights, chess.WHITE, -30) + pinned_eval(black_knights, chess.BLACK, 30) +\
pinned_eval(white_bishops,chess.WHITE, -30) + pinned_eval(black_bishops,chess.BLACK, 30) +\
pinned_eval(white_rooks,chess.WHITE, -150) + pinned_eval(black_bishops,chess.BLACK, 150) +\
pinned_eval(white_queens,chess.WHITE, -400) + pinned_eval(black_bishops,chess.BLACK, 400)
#returns value representing how many pieces of any type in list_of_pieces_to_attack are being attacked by any piece in piece_set
def attacking_eval(piece_set, list_of_pieces_to_attack,
list_of_value_of_attack):
cum_eval = 0
for piece in piece_set:
attacked = board.attacks(piece)
for i in range(0, len(list_of_pieces_to_attack)):
num_of_attacks_on_piece_type = len(
attacked.intersection(list_of_pieces_to_attack[i]))
cum_eval = cum_eval + num_of_attacks_on_piece_type * list_of_value_of_attack[
i]
return cum_eval
attacking_value = attacking_eval(white_knights, [black_queens,black_rooks,black_bishops], [20, 10, 5]) + \
attacking_eval(white_bishops, [black_queens, black_rooks, black_bishops], [20, 10, 2]) + \
attacking_eval(white_pawns, [black_queens, black_rooks, black_bishops, black_knights], [30, 20, 10, 10]) +\
attacking_eval(white_rooks, [black_queens], [20]) + \
attacking_eval(black_knights, [white_queens, white_rooks, white_bishops], [-20, -10, -5]) + \
attacking_eval(black_bishops, [white_queens, white_rooks, white_bishops], [-20, -10, -2]) + \
attacking_eval(black_pawns, [white_queens, white_rooks, white_bishops, white_knights], [-30, -20, -10, -10]) + \
attacking_eval(black_rooks, [white_queens], [-20])
num_black_minor_pieces = len(black_knights) + len(black_bishops) + len(
black_rooks)
num_white_minor_pieces = len(white_knights) + len(white_bishops) + len(
white_rooks)
#boolean if board is in endgame
endgame = (len(white_queens) + len(black_queens) is 0) or (
len(white_queens) is 1 and len(black_queens) is 1
and num_black_minor_pieces is 1 and num_white_minor_pieces is 1)
kingstable = kingstable_endgame if endgame else kingstable_middlegame
#bishop pair is more valuable
white_value_of_bishops = 375 if len(white_bishops) >= 2 and len(
black_bishops) < 2 else 360
black_value_of_bishops = 375 if len(black_bishops) >= 2 and len(
white_bishops) < 2 else 360
#calculates value of material in centipawns with standard valuations from https://en.wikipedia.org/wiki/Chess_piece_relative_value
white_material = 100 * len(white_pawns) + 350 * len(
white_knights) + white_value_of_bishops * len(
white_bishops) + 525 * len(white_rooks) + 900 * len(white_queens)
black_material = 100 * len(black_pawns) + 350 * len(
black_knights) + black_value_of_bishops * len(
black_bishops) + 525 * len(black_rooks) + 900 * len(black_queens)
#sums values of all the positions of the pieces on the board from the tables
square_values = sum([pawntable[i] for i in white_pawns]) - sum([pawntable[chess.square_mirror(i)] for i in black_pawns]) +\
sum([knightstable[i] for i in white_knights]) - sum([knightstable[chess.square_mirror(i)] for i in black_knights]) +\
sum([bishopstable[i] for i in white_bishops]) - sum([bishopstable[chess.square_mirror(i)] for i in black_bishops])+\
sum([rookstable[i] for i in white_rooks]) - sum([rookstable[chess.square_mirror(i)] for i in black_rooks])+\
sum([queenstable[i] for i in white_queens]) - sum([queenstable[chess.square_mirror(i)] for i in black_queens])+\
sum([kingstable[i] for i in white_king]) - sum([kingstable[chess.square_mirror(i)] for i in black_king])
return white_material - black_material + square_values + pinned_value + attacking_value
