# Chess engine programmed in Python

I programmed a chess AI in Python. It uses the alpha-beta algorithm with move ordering. I want it to be able to look further than depth 4, without increasing calculation time. I am wondering how I possibly could improve the efficiency of my code. I have a feeling that my code does a lot of unnecessary calculations.

king1_moved = False
king2_moved = False

rook1_left = False
rook1_right = False

rook2_left = False
rook2_right = False

iteration = 0

def game():
board = create_starting_board()
player1_pawn_promotion_line = [26, 27, 28, 29, 30, 31, 32, 33]
print_board(board)
print("")
print("")
while True:
castling = ""
# castling:
if board[110] == "r-1" and board[111] == " 0 " and board[112] == " 0 " and board[113] == " 0 " \
and board[114] == "k-1":
castling = input("Do you want to castle?")
if castling == "y":
x_piece = int(input("x_piece:"))
y_piece = int(input("y_piece:"))
x_move = int(input("x_move:"))
y_move = int(input("y_move:"))

piece_pos = (109 + x_piece) - (y_piece - 1) * 12
move_pos = (109 + x_move) - (y_move - 1) * 12

board[move_pos] = board[piece_pos]
board[piece_pos] = " 0 "

x_piece = int(input("x_piece:"))
y_piece = int(input("y_piece:"))
x_move = int(input("x_move:"))
y_move = int(input("y_move:"))

piece_pos = (109 + x_piece) - (y_piece - 1) * 12
move_pos = (109 + x_move) - (y_move - 1) * 12

board[move_pos] = board[piece_pos]
board[piece_pos] = " 0 "
if board[117] == "r-1" and board[116] == " 0 " and board[115] == " 0 " and board[114] == "k-1":
castling = input("Do you want to castle?")
if castling == "y":
x_piece = int(input("x_piece:"))
y_piece = int(input("y_piece:"))
x_move = int(input("x_move:"))
y_move = int(input("y_move:"))

piece_pos = (109 + x_piece) - (y_piece - 1) * 12
move_pos = (109 + x_move) - (y_move - 1) * 12

board[move_pos] = board[piece_pos]
board[piece_pos] = " 0 "

x_piece = int(input("x_piece:"))
y_piece = int(input("y_piece:"))
x_move = int(input("x_move:"))
y_move = int(input("y_move:"))

piece_pos = (109 + x_piece) - (y_piece - 1) * 12
move_pos = (109 + x_move) - (y_move - 1) * 12

board[move_pos] = board[piece_pos]
board[piece_pos] = " 0 "
if castling != "y":
x_piece = int(input("x_piece:"))
y_piece = int(input("y_piece:"))
x_move = int(input("x_move:"))
y_move = int(input("y_move:"))

piece_pos = (109 + x_piece) - (y_piece - 1) * 12
move_pos = (109 + x_move) - (y_move - 1) * 12

board[move_pos] = board[piece_pos]
board[piece_pos] = " 0 "

if "p-1" in board:
if board.index("p-1") in player1_pawn_promotion_line:
board[move_pos] = "q-1"

# check if king/queen has moved:
global king1_moved, rook1_right, rook1_left
if board[move_pos] == "k-1":
king1_moved = False
elif board[move_pos] == "r-1" and piece_pos == 110:
rook1_left = False
elif board[move_pos] == "r-1" and piece_pos == 117:
rook1_right = False

print_board(board)
print("")
print("")

maximize(board, -1, 4, -100000, 100000)

def sort_moves(scores, piece_positions, possible_moves,  player):

where_did_items_go = []

if player == 1:
sorted_scores = sorted(scores, reverse=True)
else:
sorted_scores = sorted(scores, reverse=False)

for item in scores:
num = sorted_scores.index(item)
while num in where_did_items_go:
num += 1
where_did_items_go.append(num)

piece = [x for _, x in sorted(zip(where_did_items_go, piece_positions))]
possible = [x for _, x in sorted(zip(where_did_items_go, possible_moves))]

return piece, possible

def maximize(board, player, depth, alpha, beta):
max_depth = 4
player2_pawn_promotion_line = [110, 111, 112, 113, 114, 115, 116, 117]
pos = -1
if depth == 0:
return evaluation(board)
max_value = alpha
positions, moves = find_all_possible_moves(board, player)
for move in moves:
pawn_promotion = False
global iteration
iteration += 1
pos += 1
# perform move
if isinstance(move, int):
piece = board[move]
board[move] = board[positions[pos]]
board[positions[pos]] = " 0 "
# pawn promotion
if "p-2" in board:
if player == -1 and board.index("p-2") in player2_pawn_promotion_line:
board[move] = "q-2"
pawn_promotion = True
value = minimize(board, player * -1, depth - 1, max_value, beta)
# reverse move
if not pawn_promotion:
board[positions[pos]] = board[move]
board[move] = piece
else:
board[positions[pos]] = "p-2"
board[move] = piece
else:
piece_1 = board[move[0]]
piece_2 = board[move[1]]
board[move[0]] = board[positions[pos][0]]
board[move[1]] = board[positions[pos][1]]
board[positions[pos][0]] = " 0 "
board[positions[pos][1]] = " 0 "
value = minimize(board, player * -1, depth - 1, max_value, beta)
# reverse move
board[positions[pos][0]] = board[move[0]]
board[positions[pos][1]] = board[move[1]]
board[move[0]] = piece_1
board[move[1]] = piece_2
if value >= max_value:
max_value = value
best_move = move
best_piece = positions[pos]
if max_value >= beta:
break
if depth == max_depth:
# perform move + check if kings/rooks moved
if moves == []:
print("Check_Mate: You won!")
exit()
if isinstance(best_move, int):
board[best_move] = board[best_piece]
board[best_piece] = " 0 "
# pawn promotion
if "p-2" in board:
if board.index("p-2") in player2_pawn_promotion_line:
board[best_move] = "q-2"
# check if king/queen has moved:
global king2_moved, rook2_right, rook2_left
if board[best_move] == "k-2":
king2_moved = True
elif board[best_move] == "r-2" and best_piece == 26:
rook2_left = True
elif board[best_move] == "r-2" and best_piece == 33:
rook2_right = True
else:
board[best_move[0]] = board[best_piece[0]]
board[best_move[1]] = board[best_piece[1]]
board[best_piece[0]] = " 0 "
board[best_piece[1]] = " 0 "
print_board(board)
print(max_value)
print(iteration)
print("")
print("")
return max_value

def minimize(board, player, depth, alpha, beta):
player1_pawn_promotion_line = [26, 27, 28, 29, 30, 31, 32, 33]
pos = -1
if depth == 0:
return evaluation(board)
min_value = beta
positions, moves = find_all_possible_moves(board, player)
for move in moves:
global iteration
iteration += 1
pawn_promotion = False
pos += 1
# perform move
if isinstance(move, int):
piece = board[move]
board[move] = board[positions[pos]]
board[positions[pos]] = " 0 "
# pawn promotion
if "p-1" in board:
if player == 1 and board.index("p-1") in player1_pawn_promotion_line:
board[move] = "q-1"
pawn_promotion = True
value = maximize(board, player * -1, depth - 1, alpha, min_value)
# reverse move
if not pawn_promotion:
board[positions[pos]] = board[move]
board[move] = piece
else:
board[positions[pos]] = "p-1"
board[move] = piece
else:
piece_1 = board[move[0]]
piece_2 = board[move[1]]
board[move[0]] = board[positions[pos][0]]
board[move[1]] = board[positions[pos][1]]
board[positions[pos][0]] = " 0 "
board[positions[pos][1]] = " 0 "
value = maximize(board, player * -1, depth - 1, alpha, min_value)
# reverse move
board[positions[pos][0]] = board[move[0]]
board[positions[pos][1]] = board[move[1]]
board[move[0]] = piece_1
board[move[1]] = piece_2
if value < min_value:
min_value = value
if min_value <= alpha:
break
return min_value

def evaluation(board):
# simple material_count
king = 3600
queen = 360
rook = 200
bishop = 120
knight = 120
pawn = 40

value = 0

search_range = [26, 27, 28, 29, 30, 31, 32, 33,
38, 39, 40, 41, 42, 43, 44, 45,
50, 51, 52, 53, 54, 55, 56, 57,
62, 63, 64, 65, 66, 67, 68, 69,
74, 75, 76, 77, 78, 79, 80, 81,
86, 87, 88, 89, 90, 91, 92, 93,
98, 99, 100, 101, 102, 103, 104, 105,
110, 111, 112, 113, 114, 115, 116, 117]

prawn_table_AI = [  0,  0,  0,  0,  0,  0,  0, 0,  0,  0, 0, 0,
0,  0,  0,  0,  0,  0,  0, 0,  0,  0, 0, 0,
0,  0,  0,  0,  0,  0,  0, 0,  0,  0, 0, 0,
0, 0, 10, 10,  5,-10,-10, 5, 10, 10, 0, 0,
0, 0, 5,  0,  5,  0,  0, 5,  0,  5, 0, 0,
0, 0, 0,  0,  5, 20, 20, 5,  0,  0, 0, 0,
0, 0, 0,  0,  0,  5,  5, 0,  0,  0, 0, 0,
0, 0, 5,  5,  5, 10, 10, 5,  5,  5, 0, 0,
0, 0, 10, 10, 10, 20, 20, 10, 10, 10, 0, 0,
0,  0,  0,  0,  0,  0,  0,  0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0]

knight_table_AI = [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, -10, 0, 0, 0, 0, -10, 0, 0, 0,
0, 0, 0, 0, 0, 5, 5, 0, 0, 0, 0, 0,
0, 0, 0, 0, 10, 10, 10, 10, 0, 0, 0, 0,
0, 0, 0, 0, 10, 15, 15, 10, 0, 0, 0, 0,
0, 0, 0, 0, 10, 15, 15, 10, 0, 0, 0, 0,
0, 0, 0, 0, 5, 10, 10, 5, 0, 0, 0, 0,
0, 0, 0, 0, 0, 5, 5, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0]

bishop_table_AI = [ 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, -10, 0, 0, -10, 0, 0, 0, 0,
0, 0,0, 0, 0, 5, 5, 0, 0, 0, 0, 0,
0, 0,0, 0, 5, 10, 10, 5, 0, 0, 0, 0,
0, 0,0, 5, 10, 15, 15, 10, 5, 0, 0, 0,
0, 0,0, 5, 10, 15, 15, 10, 5, 0, 0, 0,
0, 0,0, 0, 5, 10, 10, 5, 0, 0, 0, 0,
0, 0,0, 0, 0, 5, 5, 0, 0, 0, 0, 0,
0, 0,0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0]

rook_table_AI = [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 5, 10, 10, 5, 0, 0, 0, 0,
0, 0, 0, 0, 5, 10, 10, 5, 0, 0, 0, 0,
0, 0, 0, 0, 5, 10, 10, 5, 0, 0, 0, 0,
0, 0, 0, 0, 5, 10, 10, 5, 0, 0, 0, 0,
0, 0, 0, 0, 5, 10, 10, 5, 0, 0, 0, 0,
0, 0, 0, 0, 5, 10, 10, 5, 0, 0, 0, 0,
0, 0, 15, 15, 15, 15, 15, 15, 15, 15, 0, 0,
0, 0, 0, 0, 5, 10, 10, 5, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0]

prawn_table_H = [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 10, 10, 10, 20, 20, 10, 10, 10, 0, 0,
0, 0, 5, 5, 5, 10, 10, 5, 5, 5, 0, 0,
0, 0, 0, 0, 0, 5, 5, 0, 0, 0, 0, 0,
0, 0, 0, 0, 5, 20, 20, 5, 0, 0, 0, 0,
0, 0, 5, 0, 5, 0, 0, 5, 0, 5, 0, 0,
0, 0, 10, 10, 5, -10, -10, 5, 10, 10, 0, 0,
0, 0,0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0]

knight_table_H = [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 5, 5, 0, 0, 0, 0, 0,
0, 0, 0, 0, 5, 10, 10, 5, 0, 0, 0, 0,
0, 0, 0, 0, 10, 15, 15, 10, 0, 0, 0, 0,
0, 0, 0, 0, 10, 15, 15, 10, 0, 0, 0, 0,
0, 0, 0, 0, 10, 10, 10, 10, 0, 0, 0, 0,
0, 0, 0, 0, 0, 5, 5, 0, 0, 0, 0, 0,
0, 0, 0, -10, 0, 0, 0, 0, -10, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,]

bishop_table_H = [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 5, 5, 0, 0, 0, 0, 0,
0, 0, 0, 0, 5, 10, 10, 5, 0, 0, 0, 0,
0, 0, 0, 5, 10, 15, 15, 10, 5, 0, 0, 0,
0, 0, 0, 5, 10, 15, 15, 10, 5, 0, 0, 0,
0, 0, 0, 0, 5, 10, 10, 5, 0, 0, 0, 0,
0, 0, 0, 0, 0, 5, 5, 0, 0, 0, 0, 0,
0, 0, 0, 0, -10, 0, 0, -10, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0]

rook_table_H = [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 5, 10, 10, 5, 0, 0, 0, 0,
0, 0, 15, 15, 15, 15, 15, 15, 15, 15, 0, 0,
0, 0, 0, 0, 5, 10, 10, 5, 0, 0, 0, 0,
0, 0, 0, 0, 5, 10, 10, 5, 0, 0, 0, 0,
0, 0, 0, 0, 5, 10, 10, 5, 0, 0, 0, 0,
0, 0, 0, 0, 5, 10, 10, 5, 0, 0, 0, 0,
0, 0, 0, 0, 5, 10, 10, 5, 0, 0, 0, 0,
0, 0, 0, 0, 5, 10, 10, 5, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0]

# material_score
for square in search_range:
if "1" in board[square]:
player_string = "1"
player_int = -1
else:
player_string = "2"
player_int = 1

if "p-" + player_string in board[square]:
value = value + player_int * pawn
if "n-" + player_string in board[square]:
value = value + player_int * knight
if "b-" + player_string in board[square]:
value = value + player_int * bishop
if "r-" + player_string in board[square]:
value = value + player_int * rook
if "q-" + player_string in board[square]:
value = value + player_int * queen
if "k-" + player_string in board[square]:
value = value + player_int * king

# position score
for square in search_range:
if "1" in board[square]:
if "p" in board[square]:
value -= prawn_table_H[square]
if "b" in board[square]:
value -= bishop_table_H[square]
if "n" in board[square]:
value -= knight_table_H[square]
if "r" in board[square]:
value -= rook_table_H[square]
else:
if "p" in board[square]:
value += prawn_table_AI[square]
if "b" in board[square]:
value += bishop_table_AI[square]
if "n" in board[square]:
value += knight_table_AI[square]
if "r" in board[square]:
value += rook_table_AI[square]

# Castling
if board[31] == "r-2" and board[32] == "k-2":
value += 4
if board[29] == "r-2" and board[28] == "k-2":
value += 4
if board[115] == "r-1" and board[116] == "k-1":
value -= 4
if board[113] == "r-1" and board[112] == "k-1":
value -= 4

return value

def create_starting_board():
board = ["x", "x", "x", "x", "x", "x", "x", "x", "x", "x", "x", "x",
"x", "x", "x", "x", "x", "x", "x", "x", "x", "x", "x", "x",
"x", "x", "r-2", "n-2", "b-2", "q-2", "k-2", "b-2", "n-2", "r-2", "x", "x",
"x", "x", "p-2", "p-2", "p-2", "p-2", "p-2", "p-2", "p-2", "p-2", "x", "x",
"x", "x", " 0 ", " 0 ", " 0 ", " 0 ", " 0 ", " 0 ", " 0 ", " 0 ", "x", "x",
"x", "x", " 0 ", " 0 ", " 0 ", " 0 ", " 0 ", " 0 ", " 0 ", " 0 ", "x", "x",
"x", "x", " 0 ", " 0 ", " 0 ", " 0 ", " 0 ", " 0 ", " 0 ", " 0 ", "x", "x",
"x", "x", " 0 ", " 0 ", " 0 ", " 0 ", " 0 ", " 0 ", " 0 ", " 0 ", "x", "x",
"x", "x", "p-1", "p-1", "p-1", "p-1", "p-1", "p-1", "p-1", "p-1", "x", "x",
"x", "x", "r-1", "n-1", "b-1", "q-1", "k-1", "b-1", "n-1", "r-1", "x", "x",
"x", "x", "x", "x", "x", "x", "x", "x", "x", "x", "x", "x",
"x", "x", "x", "x", "x", "x", "x", "x", "x", "x", "x", "x"]
return board

def print_board(board):
for i in range(8):
if i > 0:
print("---------------------------------")
print("¦" + board[26 + i * 12] + "¦" + board[12 * i + 27] + "¦" + board[12 * i + 28] + "¦" + board[
i * 12 + 29] + "¦" + board[12 * i + 30] + "¦" + board[12 * i + 31] + "¦" + board[12 * i + 32] + "¦"
+ board[12 * i + 33] + "¦")

def king_exists(board, player):
search_range = [26, 27, 28, 29, 30, 31, 32, 33,
38, 39, 40, 41, 42, 43, 44, 45,
50, 51, 52, 53, 54, 55, 56, 57,
62, 63, 64, 65, 66, 67, 68, 69,
74, 75, 76, 77, 78, 79, 80, 81,
86, 87, 88, 89, 90, 91, 92, 93,
98, 99, 100, 101, 102, 103, 104, 105,
110, 111, 112, 113, 114, 115, 116, 117]
if player == 1:
player_string = "1"
else:
player_string = "2"
for i in search_range:
if "k-" + player_string in board[i]:
return True
return False

def king_under_attack(board, player):
position, moves = make_all_next_moves(board, player * -1)
pos = -1
player1_pawn_promotion_line = [26, 27, 28, 29, 30, 31, 32, 33]
player2_pawn_promotion_line = [110, 111, 112, 113, 114, 115, 116, 117]
# perform all moves and check if in one of the moves the king doesn't exist, if true, then the king is under check
# in the current board_state
for move in moves:
pawn_promotion = False
pos += 1
if isinstance(move, int):
piece = board[move]
board[move] = board[position[pos]]
board[position[pos]] = " 0 "
# pawn promotion
if "p-1" in board:
if player == 1 and board.index("p-1") in player1_pawn_promotion_line:
board[move] = "q-1"
pawn_promotion = True
if "p-2" in board:
if player == -1 and board.index("p-2") in player2_pawn_promotion_line:
board[move] = "q-2"
pawn_promotion = True
if not king_exists(board, player):
# reverse move
if not pawn_promotion:
board[position[pos]] = board[move]
board[move] = piece
else:
if player == 1:
board[position[pos]] = "p-1"
board[move] = piece
else:
board[position[pos]] = "p-2"
board[move] = piece
return True
# reverse move
if not pawn_promotion:
board[position[pos]] = board[move]
board[move] = piece
else:
if player == 1:
board[position[pos]] = "p-1"
board[move] = piece
else:
board[position[pos]] = "p-2"
board[move] = piece

else:
piece_1 = board[move[0]]
piece_2 = board[move[1]]
board[move[0]] = board[position[pos][0]]
board[move[1]] = board[position[pos][1]]
board[position[pos][0]] = " 0 "
board[position[pos][1]] = " 0 "
if not king_exists(board, player):
# reverse move
board[position[pos][0]] = board[move[0]]
board[position[pos][1]] = board[move[1]]
board[move[0]] = piece_1
board[move[1]] = piece_2
return True
# reverse move
board[position[pos][0]] = board[move[0]]
board[position[pos][1]] = board[move[1]]
board[move[0]] = piece_1
board[move[1]] = piece_2
return False

def make_all_next_moves(board, player):
possible_moves = []
piece_position = []
search_range = [26, 27, 28, 29, 30, 31, 32, 33,
38, 39, 40, 41, 42, 43, 44, 45,
50, 51, 52, 53, 54, 55, 56, 57,
62, 63, 64, 65, 66, 67, 68, 69,
74, 75, 76, 77, 78, 79, 80, 81,
86, 87, 88, 89, 90, 91, 92, 93,
98, 99, 100, 101, 102, 103, 104, 105,
110, 111, 112, 113, 114, 115, 116, 117]
pawn1_start = [98, 99, 100, 101, 102, 103, 104, 105]
pawn2_start = [38, 39, 40, 41, 42, 43, 44, 45]

if player == 1:
player_string = "1"
attack_player = "2"
pawn_starting_positions = pawn1_start
else:
player_string = "2"
attack_player = "1"
pawn_starting_positions = pawn2_start
# find all possible moves with pawn, bishop, knight, rook, queen and king
for i in search_range:
# pawn
if "p-" + player_string in board[i]:
# pawn_forward
if board[i - player * 12] == " 0 ":
piece_position.append(i)
possible_moves.append(i - player * 12)
# pawn_right
if attack_player in board[i - player * 11]:
piece_position.append(i)
possible_moves.append(i - player * 11)
# pawn_left
if attack_player in board[i - player * 13]:
piece_position.append(i)
possible_moves.append(i - player * 13)
# pawn_two_forward
if board[i - player * 24] == " 0 " and board[i - player * 12] == " 0 " and i in pawn_starting_positions:
piece_position.append(i)
possible_moves.append(i - player * 24)

# bishop
if "b-" + player_string in board[i]:
# bishop_up_right
x = i
while True:
x = x - 11
if board[x] == " 0 ":
piece_position.append(i)
possible_moves.append(x)
elif attack_player in board[x]:
piece_position.append(i)
possible_moves.append(x)
break
else:
break
# bishop_up_left
x = i
while True:
x = x - 13
if board[x] == " 0 ":
piece_position.append(i)
possible_moves.append(x)
elif attack_player in board[x]:
piece_position.append(i)
possible_moves.append(x)
break
else:
break
# bishop_down_left
x = i
while True:
x = x + 11
if board[x] == " 0 ":
piece_position.append(i)
possible_moves.append(x)
elif attack_player in board[x]:
piece_position.append(i)
possible_moves.append(x)
break
else:
break
# bishop_down_right
x = i
while True:
x = x + 13
if board[x] == " 0 ":
piece_position.append(i)
possible_moves.append(x)
elif attack_player in board[x]:
piece_position.append(i)
possible_moves.append(x)
break
else:
break
# knight
if "n-" + player_string in board[i]:
# 8 cases
if " 0 " in board[i - 23] or attack_player in board[i - 23]:
piece_position.append(i)
possible_moves.append(i - 23)
if " 0 " in board[i - 25] or attack_player in board[i - 25]:
piece_position.append(i)
possible_moves.append(i - 25)
if " 0 " in board[i - 10] or attack_player in board[i - 10]:
piece_position.append(i)
possible_moves.append(i - 10)
if " 0 " in board[i - 14] or attack_player in board[i - 14]:
piece_position.append(i)
possible_moves.append(i - 14)
if " 0 " in board[i + 23] or attack_player in board[i + 23]:
piece_position.append(i)
possible_moves.append(i + 23)
if " 0 " in board[i + 25] or attack_player in board[i + 25]:
piece_position.append(i)
possible_moves.append(i + 25)
if " 0 " in board[i + 10] or attack_player in board[i + 10]:
piece_position.append(i)
possible_moves.append(i + 10)
if " 0 " in board[i + 14] or attack_player in board[i + 14]:
piece_position.append(i)
possible_moves.append(i + 14)
# rook
if "r-" + player_string in board[i]:
# rook_up
x = i
while True:
x = x - 12
if board[x] == " 0 ":
piece_position.append(i)
possible_moves.append(x)
elif attack_player in board[x]:
piece_position.append(i)
possible_moves.append(x)
break
else:
break
# rook_down
x = i
while True:
x = x + 12
if board[x] == " 0 ":
piece_position.append(i)
possible_moves.append(x)
elif attack_player in board[x]:
piece_position.append(i)
possible_moves.append(x)
break
else:
break
# rook_right
x = i
while True:
x = x + 1
if board[x] == " 0 ":
piece_position.append(i)
possible_moves.append(x)
elif attack_player in board[x]:
piece_position.append(i)
possible_moves.append(x)
break
else:
break
# rook_left
x = i
while True:
x = x - 1
if board[x] == " 0 ":
piece_position.append(i)
possible_moves.append(x)
elif attack_player in board[x]:
piece_position.append(i)
possible_moves.append(x)
break
else:
break
# queen
if "q-" + player_string in board[i]:
# queen_up
x = i
while True:
x = x - 12
if board[x] == " 0 ":
piece_position.append(i)
possible_moves.append(x)
elif attack_player in board[x]:
piece_position.append(i)
possible_moves.append(x)
break
else:
break
# queen_down
x = i
while True:
x = x + 12
if board[x] == " 0 ":
piece_position.append(i)
possible_moves.append(x)
elif attack_player in board[x]:
piece_position.append(i)
possible_moves.append(x)
break
else:
break
# queen_right
x = i
while True:
x = x + 1
if board[x] == " 0 ":
piece_position.append(i)
possible_moves.append(x)
elif attack_player in board[x]:
piece_position.append(i)
possible_moves.append(x)
break
else:
break
# queen_left
x = i
while True:
x = x - 1
if board[x] == " 0 ":
piece_position.append(i)
possible_moves.append(x)
elif attack_player in board[x]:
piece_position.append(i)
possible_moves.append(x)
break
else:
break
# queen_up_right
x = i
while True:
x = x - 11
if board[x] == " 0 ":
piece_position.append(i)
possible_moves.append(x)
elif attack_player in board[x]:
piece_position.append(i)
possible_moves.append(x)
break
else:
break
# queen_up_left
x = i
while True:
x = x - 13
if board[x] == " 0 ":
piece_position.append(i)
possible_moves.append(x)
elif attack_player in board[x]:
piece_position.append(i)
possible_moves.append(x)
break
else:
break
# queen_down_left
x = i
while True:
x = x + 11
if board[x] == " 0 ":
piece_position.append(i)
possible_moves.append(x)
elif attack_player in board[x]:
piece_position.append(i)
possible_moves.append(x)
break
else:
break
# queen_down_right
x = i
while True:
x = x + 13
if board[x] == " 0 ":
piece_position.append(i)
possible_moves.append(x)
elif attack_player in board[x]:
piece_position.append(i)
possible_moves.append(x)
break
else:
break
# king
if "k-" + player_string in board[i]:
# king_up
if " 0 " in board[i - 12] or attack_player in board[i - 12]:
piece_position.append(i)
possible_moves.append(i - 12)
# king_down
if " 0 " in board[i + 12] or attack_player in board[i + 12]:
piece_position.append(i)
possible_moves.append(i + 12)
# king_right
if " 0 " in board[i + 1] or attack_player in board[i + 1]:
piece_position.append(i)
possible_moves.append(i + 1)
# king_left
if " 0 " in board[i - 1] or attack_player in board[i - 1]:
piece_position.append(i)
possible_moves.append(i - 1)
# king_up_right
if " 0 " in board[i - 11] or attack_player in board[i - 11]:
piece_position.append(i)
possible_moves.append(i - 11)
# king_up_left
if " 0 " in board[i - 13] or attack_player in board[i - 13]:
piece_position.append(i)
possible_moves.append(i - 13)
# king_down_right
if " 0 " in board[i + 11] or attack_player in board[i + 11]:
piece_position.append(i)
possible_moves.append(i + 11)
# king_down_left
if " 0 " in board[i + 13] or attack_player in board[i + 13]:
piece_position.append(i)
possible_moves.append(i + 13)
# Castling
global king1_moved, king2_moved, rook1_left, rook1_right, rook2_left, rook2_right
if player == 1 and not king1_moved:
# 2 castling options
if board[110] == "r-1" and board[111] == " 0 " and board[112] == " 0 " \
and board[113] == " 0 " and board[114] == "k-1" and not rook1_left:
piece_position.append([114, 110])
possible_moves.append([112, 113])
if board[117] == "r-1" and board[116] == " 0 " and board[115] == " 0 " \
and board[114] == "k-1" and not rook1_right:
piece_position.append([114, 117])
possible_moves.append([116, 115])
if player == -1 and not king2_moved:
# 2 castling options
if board[26] == "r-2" and board[27] == " 0 " and board[28] == " 0 " \
and board[29] == " 0 " and board[30] == "k-2" and not rook2_left:
piece_position.append([30, 26])
possible_moves.append([28, 29])
if board[33] == "r-2" and board[32] == " 0 " and board[31] == " 0 " \
and board[30] == "k-2" and not rook2_right:
piece_position.append([30, 33])
possible_moves.append([32, 31])

# En passe --> maybe add it later on (a bit unnessecary but okay i guess i'll just add it later)

return piece_position, possible_moves

def find_all_possible_moves(board, player):
possible_moves = []
piece_position = []
search_range = [26, 27, 28, 29, 30, 31, 32, 33,
38, 39, 40, 41, 42, 43, 44, 45,
50, 51, 52, 53, 54, 55, 56, 57,
62, 63, 64, 65, 66, 67, 68, 69,
74, 75, 76, 77, 78, 79, 80, 81,
86, 87, 88, 89, 90, 91, 92, 93,
98, 99, 100, 101, 102, 103, 104, 105,
110, 111, 112, 113, 114, 115, 116, 117]
pawn1_start = [98, 99, 100, 101, 102, 103, 104, 105]
pawn2_start = [38, 39, 40, 41, 42, 43, 44, 45]

if player == 1:
player_string = "1"
attack_player = "2"
pawn_starting_positions = pawn1_start
else:
player_string = "2"
attack_player = "1"
pawn_starting_positions = pawn2_start
# find all possible moves with pawn, bishop, knight, rook, queen and king
for i in search_range:
# pawn
if "p-" + player_string in board[i]:
# pawn_forward
if board[i - player * 12] == " 0 ":
piece_position.append(i)
possible_moves.append(i - player * 12)
# pawn_right
if attack_player in board[i - player * 11]:
piece_position.append(i)
possible_moves.append(i - player * 11)
# pawn_left
if attack_player in board[i - player * 13]:
piece_position.append(i)
possible_moves.append(i - player * 13)
# pawn_two_forward
if board[i - player * 24] == " 0 " and board[i - player * 12] == " 0 " and i in pawn_starting_positions:
piece_position.append(i)
possible_moves.append(i - player * 24)
# bishop
if "b-" + player_string in board[i]:
# bishop_up_right
x = i
while True:
x = x - 11
if board[x] == " 0 ":
piece_position.append(i)
possible_moves.append(x)
elif attack_player in board[x]:
piece_position.append(i)
possible_moves.append(x)
break
else:
break
# bishop_up_left
x = i
while True:
x = x - 13
if board[x] == " 0 ":
piece_position.append(i)
possible_moves.append(x)
elif attack_player in board[x]:
piece_position.append(i)
possible_moves.append(x)
break
else:
break
# bishop_down_left
x = i
while True:
x = x + 11
if board[x] == " 0 ":
piece_position.append(i)
possible_moves.append(x)
elif attack_player in board[x]:
piece_position.append(i)
possible_moves.append(x)
break
else:
break
# bishop_down_right
x = i
while True:
x = x + 13
if board[x] == " 0 ":
piece_position.append(i)
possible_moves.append(x)
elif attack_player in board[x]:
piece_position.append(i)
possible_moves.append(x)
break
else:
break
# knight
if "n-" + player_string in board[i]:
# 8 cases
if " 0 " in board[i - 23] or attack_player in board[i - 23]:
piece_position.append(i)
possible_moves.append(i - 23)
if " 0 " in board[i - 25] or attack_player in board[i - 25]:
piece_position.append(i)
possible_moves.append(i - 25)
if " 0 " in board[i - 10] or attack_player in board[i - 10]:
piece_position.append(i)
possible_moves.append(i - 10)
if " 0 " in board[i - 14] or attack_player in board[i - 14]:
piece_position.append(i)
possible_moves.append(i - 14)
if " 0 " in board[i + 23] or attack_player in board[i + 23]:
piece_position.append(i)
possible_moves.append(i + 23)
if " 0 " in board[i + 25] or attack_player in board[i + 25]:
piece_position.append(i)
possible_moves.append(i + 25)
if " 0 " in board[i + 10] or attack_player in board[i + 10]:
piece_position.append(i)
possible_moves.append(i + 10)
if " 0 " in board[i + 14] or attack_player in board[i + 14]:
piece_position.append(i)
possible_moves.append(i + 14)
# rook
if "r-" + player_string in board[i]:
# rook_up
x = i
while True:
x = x - 12
if board[x] == " 0 ":
piece_position.append(i)
possible_moves.append(x)
elif attack_player in board[x]:
piece_position.append(i)
possible_moves.append(x)
break
else:
break
# rook_down
x = i
while True:
x = x + 12
if board[x] == " 0 ":
piece_position.append(i)
possible_moves.append(x)
elif attack_player in board[x]:
piece_position.append(i)
possible_moves.append(x)
break
else:
break
# rook_right
x = i
while True:
x = x + 1
if board[x] == " 0 ":
piece_position.append(i)
possible_moves.append(x)
elif attack_player in board[x]:
piece_position.append(i)
possible_moves.append(x)
break
else:
break
# rook_left
x = i
while True:
x = x - 1
if board[x] == " 0 ":
piece_position.append(i)
possible_moves.append(x)
elif attack_player in board[x]:
piece_position.append(i)
possible_moves.append(x)
break
else:
break
# queen
if "q-" + player_string in board[i]:
# queen_up
x = i
while True:
x = x - 12
if board[x] == " 0 ":
piece_position.append(i)
possible_moves.append(x)
elif attack_player in board[x]:
piece_position.append(i)
possible_moves.append(x)
break
else:
break
# queen_down
x = i
while True:
x = x + 12
if board[x] == " 0 ":
piece_position.append(i)
possible_moves.append(x)
elif attack_player in board[x]:
piece_position.append(i)
possible_moves.append(x)
break
else:
break
# queen_right
x = i
while True:
x = x + 1
if board[x] == " 0 ":
piece_position.append(i)
possible_moves.append(x)
elif attack_player in board[x]:
piece_position.append(i)
possible_moves.append(x)
break
else:
break
# queen_left
x = i
while True:
x = x - 1
if board[x] == " 0 ":
piece_position.append(i)
possible_moves.append(x)
elif attack_player in board[x]:
piece_position.append(i)
possible_moves.append(x)
break
else:
break
# queen_up_right
x = i
while True:
x = x - 11
if board[x] == " 0 ":
piece_position.append(i)
possible_moves.append(x)
elif attack_player in board[x]:
piece_position.append(i)
possible_moves.append(x)
break
else:
break
# queen_up_left
x = i
while True:
x = x - 13
if board[x] == " 0 ":
piece_position.append(i)
possible_moves.append(x)
elif attack_player in board[x]:
piece_position.append(i)
possible_moves.append(x)
break
else:
break
# queen_down_left
x = i
while True:
x = x + 11
if board[x] == " 0 ":
piece_position.append(i)
possible_moves.append(x)
elif attack_player in board[x]:
piece_position.append(i)
possible_moves.append(x)
break
else:
break
# queen_down_right
x = i
while True:
x = x + 13
if board[x] == " 0 ":
piece_position.append(i)
possible_moves.append(x)
elif attack_player in board[x]:
piece_position.append(i)
possible_moves.append(x)
break
else:
break
# king
if "k-" + player_string in board[i]:
# king_up
if " 0 " in board[i - 12] or attack_player in board[i - 12]:
piece_position.append(i)
possible_moves.append(i - 12)
# king_down
if " 0 " in board[i + 12] or attack_player in board[i + 12]:
piece_position.append(i)
possible_moves.append(i + 12)
# king_right
if " 0 " in board[i + 1] or attack_player in board[i + 1]:
piece_position.append(i)
possible_moves.append(i + 1)
# king_left
if " 0 " in board[i - 1] or attack_player in board[i - 1]:
piece_position.append(i)
possible_moves.append(i - 1)
# king_up_right
if " 0 " in board[i - 11] or attack_player in board[i - 11]:
piece_position.append(i)
possible_moves.append(i - 11)
# king_up_left
if " 0 " in board[i - 13] or attack_player in board[i - 13]:
piece_position.append(i)
possible_moves.append(i - 13)
# king_down_right
if " 0 " in board[i + 11] or attack_player in board[i + 11]:
piece_position.append(i)
possible_moves.append(i + 11)
# king_down_left
if " 0 " in board[i + 13] or attack_player in board[i + 13]:
piece_position.append(i)
possible_moves.append(i + 13)

# Castling
global king1_moved, king2_moved, rook1_left, rook1_right, rook2_left, rook2_right
if not king_under_attack(board, player):
if player == 1 and not king1_moved:
# 2 castling options
if board[110] == "r-1" and board[111] == " 0 " and board[112] == " 0 " \
and board[113] == " 0 " and board[114] == "k-1" and not rook1_left:
piece_position.append([114, 110])
possible_moves.append([112, 113])
if board[117] == "r-1" and board[116] == " 0 " and board[115] == " 0 " \
and board[114] == "k-1" and not rook1_right:
piece_position.append([114, 117])
possible_moves.append([116, 115])
if player == -1 and not king2_moved:
# 2 castling options
if board[26] == "r-2" and board[27] == " 0 " and board[28] == " 0 " \
and board[29] == " 0 " and board[30] == "k-2" and not rook2_left:
piece_position.append([30, 26])
possible_moves.append([28, 29])
if board[33] == "r-2" and board[32] == " 0 " and board[31] == " 0 " \
and board[30] == "k-2" and not rook2_right:
piece_position.append([30, 33])
possible_moves.append([32, 31])

scores = []
player1_pawn_promotion_line = [26, 27, 28, 29, 30, 31, 32, 33]
player2_pawn_promotion_line = [110, 111, 112, 113, 114, 115, 116, 117]
for i in range(len(possible_moves) - 1, -1, -1):
pawn_promotion = False
deletion = False
if isinstance(possible_moves[i], int):
piece = board[possible_moves[i]]
board[possible_moves[i]] = board[piece_position[i]]
board[piece_position[i]] = " 0 "
# pawn promotion
if "p-1" in board:
if player == 1 and board.index("p-1") in player1_pawn_promotion_line:
board[possible_moves[i]] = "q-1"
pawn_promotion = True
if "p-2" in board:
if player == -1 and board.index("p-2") in player2_pawn_promotion_line:
board[possible_moves[i]] = "q-2"
pawn_promotion = True
if king_under_attack(board, player):
deletion = True
else:
# add score for move ordering
scores.append(evaluation(board))
# reverse move
if not pawn_promotion:
board[piece_position[i]] = board[possible_moves[i]]
board[possible_moves[i]] = piece
else:
if player == 1:
board[piece_position[i]] = "p-1"
board[possible_moves[i]] = piece
else:
board[piece_position[i]] = "p-2"
board[possible_moves[i]] = piece
else:
piece_1 = board[possible_moves[i][0]]
piece_2 = board[possible_moves[i][1]]
board[possible_moves[i][0]] = board[piece_position[i][0]]
board[possible_moves[i][1]] = board[piece_position[i][1]]
board[piece_position[i][0]] = " 0 "
board[piece_position[i][1]] = " 0 "
if king_under_attack(board, player):
deletion = True
else:
# add score for move ordering
scores.append(evaluation(board))
# reverse move
board[piece_position[i][0]] = board[possible_moves[i][0]]
board[piece_position[i][1]] = board[possible_moves[i][1]]
board[possible_moves[i][0]] = piece_1
board[possible_moves[i][1]] = piece_2
if deletion:
del possible_moves[i]
del piece_position[i]

# En passe --> maybe add it later on (a bit unnecessary but okay i guess i'll just add it later)

piece_position, possible_moves = sort_moves(scores, piece_position,possible_moves, player)

return piece_position, possible_moves

game()


Here is a description of how my program works:

This is one of my first attempts on making a chess-AI. It uses alpha-beta pruning with move ordering. The program isn't finished, but it is already usable. It knows about pawn promotion and castling, but I haven't yet implemented En passet. It currently searches at a depth of 4.

How to use it: When you start it up, the board will be printed out and the human starts playing with the white pieces. The human player has to enter the coordinates of the piece to move and after that, the coordinates where he wants to move the selected piece too (Unlike in the AI-functions I have currently not implemented a function, which would only allow legal moves by the human.) After that, the updated board is printed.

¦r-2¦n-2¦b-2¦q-2¦k-2¦b-2¦n-2¦r-2¦
---------------------------------
¦p-2¦p-2¦p-2¦p-2¦p-2¦p-2¦p-2¦p-2¦
---------------------------------
¦ 0 ¦ 0 ¦ 0 ¦ 0 ¦ 0 ¦ 0 ¦ 0 ¦ 0 ¦
---------------------------------
¦ 0 ¦ 0 ¦ 0 ¦ 0 ¦ 0 ¦ 0 ¦ 0 ¦ 0 ¦
---------------------------------
¦ 0 ¦ 0 ¦ 0 ¦ 0 ¦ 0 ¦ 0 ¦ 0 ¦ 0 ¦
---------------------------------
¦ 0 ¦ 0 ¦ 0 ¦ 0 ¦ 0 ¦ 0 ¦ 0 ¦ 0 ¦
---------------------------------
¦p-1¦p-1¦p-1¦p-1¦p-1¦p-1¦p-1¦p-1¦
---------------------------------
¦r-1¦n-1¦b-1¦q-1¦k-1¦b-1¦n-1¦r-1¦

x_piece:4
y_piece:2
x_move:4
y_move:4

¦r-2¦n-2¦b-2¦q-2¦k-2¦b-2¦n-2¦r-2¦
---------------------------------
¦p-2¦p-2¦p-2¦p-2¦p-2¦p-2¦p-2¦p-2¦
---------------------------------
¦ 0 ¦ 0 ¦ 0 ¦ 0 ¦ 0 ¦ 0 ¦ 0 ¦ 0 ¦
---------------------------------
¦ 0 ¦ 0 ¦ 0 ¦ 0 ¦ 0 ¦ 0 ¦ 0 ¦ 0 ¦
---------------------------------
¦ 0 ¦ 0 ¦ 0 ¦p-1¦ 0 ¦ 0 ¦ 0 ¦ 0 ¦
---------------------------------
¦ 0 ¦ 0 ¦ 0 ¦ 0 ¦ 0 ¦ 0 ¦ 0 ¦ 0 ¦
---------------------------------
¦p-1¦p-1¦p-1¦ 0 ¦p-1¦p-1¦p-1¦p-1¦
---------------------------------
¦r-1¦n-1¦b-1¦q-1¦k-1¦b-1¦n-1¦r-1¦


Then, it's the AI's turn. It tries to find the best move with alpha-beta pruning (with move ordering). The evaluation function takes into consideration: the position of the pieces (with the help of hash tables) and material balance. When it finishes calculating, it performs the move and prints the updated board. Under the board, it spits out its predicted score and under that the number of chess boards it searched through:

¦r-2¦n-2¦b-2¦q-2¦k-2¦b-2¦n-2¦r-2¦
---------------------------------
¦p-2¦p-2¦ 0 ¦p-2¦p-2¦p-2¦p-2¦p-2¦
---------------------------------
¦ 0 ¦ 0 ¦p-2¦ 0 ¦ 0 ¦ 0 ¦ 0 ¦ 0 ¦
---------------------------------
¦ 0 ¦ 0 ¦ 0 ¦ 0 ¦ 0 ¦ 0 ¦ 0 ¦ 0 ¦
---------------------------------
¦ 0 ¦ 0 ¦ 0 ¦p-1¦ 0 ¦ 0 ¦ 0 ¦ 0 ¦
---------------------------------
¦ 0 ¦ 0 ¦ 0 ¦ 0 ¦ 0 ¦ 0 ¦ 0 ¦ 0 ¦
---------------------------------
¦p-1¦p-1¦p-1¦ 0 ¦p-1¦p-1¦p-1¦p-1¦
---------------------------------
¦r-1¦n-1¦b-1¦q-1¦k-1¦b-1¦n-1¦r-1¦

25                                              <--- score prediction

141936                                          <--- amount of searched chess
boards


The goal with this project is to make an AI which outperforms decent chess players. I would like it to reach an ELO somewhere around 1600, but in order to do that, my number 1 priority is to improve the search depth. The problem with this is that it already takes an age to search at depth 4. I wonder if anyone could help me and point at some improvements I could make. My programming skills are quite basic and I probably should comment my code better.

• Traditionally White and Black pieces are represented with upper- and lowercase letters respectively. -1 and -2 look noisy.
– vnp
Jan 30, 2019 at 17:15
• Ah okay thanks, I'll probably be changing this sometime in the future. Jan 31, 2019 at 10:31

Your functions are really long. For example game() has 88 lines.
Some parts are extracted (great!), for example print_board(). I would do the same for example with castling code that is really long and move it to its own function.