Код зависает

from random import randint, choice
 
import numpy
 
import pygame
 
pygame.init()
screen = pygame.display.set_mode((550, 650))
pygame.display.set_caption('2048')
icon = pygame.image.load('icon.ico')
pygame.display.set_icon(icon)
screen.fill((255, 246, 230))
myfont = pygame.font.Font('Roboto-Light.ttf', 50)
FILE_NAME = '2048_high_score.txt'
n = 1
square = pygame.Surface((450, 450))
square.fill(color=(121, 112, 99))
 
colors = [
    [240, 228, 217],
    [238, 225, 199],
    [253, 175, 112],
    [255, 143, 86],
    [255, 112, 80],
    [255, 70, 18],
    [241, 210, 104],
    [241, 208, 86],
    [240, 203, 65],
    [242, 201, 39],
    [243, 197, 0],
    [255, 80, 75],
    [255, 34, 75],
    [248, 19, 30],
    [96, 178, 219],
    [83, 154, 229],
    [0, 118, 193]
]
 
 
def draw_field():
    for i in range(0, 16):
        width = i % 4
        height = i // 4
        pygame.draw.rect(square, color=(216, 206, 196),
                         rect=(width * 100 + 10 * width + 10, height * 100 + 10 * height + 10, 100, 100))
 
 
def get_new_board():
    global board
    board = [0 for _ in range(16)]
    add_random_number(board)
    return board
 
 
def add_random_number(board):
    number = 4 if randint(1, 10) == 1 else 2
    empty_cells = []
    for i in range(len(board)):
        if board[i] == 0:
            empty_cells.append(i)
    board[choice(empty_cells)] = number
 
 
def draw_rect(board):
    square.fill(color=(121, 112, 99))
    for (i, el) in enumerate(board):
        if el != 0:
            width = i % 4
            height = i // 4
            el2 = int(numpy.log2(el))
            rect = pygame.draw.rect(square, color=(colors[el2]),
                                    rect=(width * 100 + 10 * width + 10, height * 100 + 10 * height + 10, 100, 100))
            text = myfont.render(f'{el}', True, 'Black')
            place = text.get_rect(center=(width * 100 + 10 * width + 110, 200 + height * 100 + 10 * height + 10))
            screen.blit(text, place)
 
 
def get_high_score():
    try:
        with open(FILE_NAME) as file:
            data = file.read().strip().split()
            if len(data) == 2 and data[0].isdecimal() and data[1].isdecimal():
                checksum = round((int(data[1], 8) - 123456789) / 123456789)
                if checksum == int(data[0]):
                    return int(data[0])
            print('Файл с лучшим результатом содержит некорректные данные')
            return 0
    except FileNotFoundError:
        return 0
 
 
def board_is_full(board):
    for cell in board:
        if cell == 0:
            return False
    return True
 
 
def get_valid_move():
    move = input('Введите W, A, S или D для выбора направления или R для окончания: ').lower()
    while move not in tuple('wasdr'):
        move = input('Введите W, A, S, D или R: ')
    print()
    return move
 
 
def move_up(board):
    score = 0
    merged = []
    for i in range(4, 16):
        while i > 3 and board[i - 4] == 0:
            board[i - 4] = board[i]
            board[i] = 0
            i -= 4
        if i > 3 and board[i - 4] == board[i] and i - 4 not in merged:
            board[i - 4] *= 2
            merged.append(i - 4)
            score += board[i - 4]
            board[i] = 0
    return score
 
 
def move_left(board):
    score = 0
    merged = []
    for n in range(1, 4):
        for i in range(n, n + 13, 4):
            while i not in (0, 4, 8, 12) and board[i - 1] == 0:
                board[i - 1] = board[i]
                board[i] = 0
                i -= 1
            if i not in (0, 4, 8, 12) and board[i - 1] == board[i] and i - 1 not in merged:
                board[i - 1] *= 2
                merged.append(i - 1)
                score += board[i - 1]
                board[i] = 0
    return score
 
 
def move_down(board):
    score = 0
    merged = []
    for i in range(11, -1, -1):
        while i < 12 and board[i + 4] == 0:
            board[i + 4] = board[i]
            board[i] = 0
            i += 4
        if i < 12 and board[i + 4] == board[i] and i + 4 not in merged:
            board[i + 4] *= 2
            merged.append(i + 4)
            score += board[i + 4]
            board[i] = 0
    return score
 
 
def move_right(board):
    score = 0
    merged = []
    for n in range(2, -1, -1):
        for i in range(n, n + 13, 4):
            while i not in (3, 7, 11, 15) and board[i + 1] == 0:
                board[i + 1] = board[i]
                board[i] = 0
                i += 1
            if i not in (3, 7, 11, 15) and board[i + 1] == board[i] and i + 1 not in merged:
                board[i + 1] *= 2
                merged.append(i + 1)
                score += board[i + 1]
                board[i] = 0
    return score
 
 
def get_valid_answer():
    answer = input('Хотите сыграть снова? (да/нет): ').lower()
    while answer not in ('да', 'нет'):
        answer = input('Просто ответьте \"да\" или \"нет\": ').lower()
    print()
    return False if answer == 'нет' else True
 
 
def print_results(board, score, high_score):
    if has_won(board):
        print('Поздравляю! Вы выиграли!')
    else:
        print('К сожалению, вы проиграли...')
    print(f'Ваш финальный результат: {score}')
    if score == high_score and score > 0:
        print('Ваш результат лучший!')
    print()
 
 
def has_won(board):
    has_won = False
    for cell in board:
        if cell >= 2048:
            return True
    return False
 
 
def save_high_score(high_score):
    try:
        with open(FILE_NAME, 'w') as file:
            checksum = oct(high_score * 123456789 + 123456789)
            file.write(str(high_score) + ' ' + str(checksum)[2:])
    except OSError:
        print('Невозможно записать лучший результат в файл.\n')
 
 
draw_field()
get_new_board()
screen.blit(square, (50, 150))
draw_rect(board)
pygame.display.update()
 
running = True
while running:
    pygame.time.delay(1)
    high_score = get_high_score()
    wants_to_play = True
    while wants_to_play:
        board = get_new_board()
        score = 0
        move = None
        while not (board_is_full(board)):
            if n == 1:
                add_random_number(board)
                draw_rect(board)
                n = 0
            keys = pygame.key.get_pressed()
            if keys[pygame.K_UP]:
                score += move_up(board)
                n = 1
            elif keys[pygame.K_LEFT]:
                score += move_left(board)
                n = 1
            elif keys[pygame.K_DOWN]:
                score += move_down(board)
                n = 1
            elif keys[pygame.K_RIGHT]:
                score += move_right(board)
                n = 1
            if score > high_score:
                high_score = score
            pygame.display.update()
        draw_rect(board)
        print_results(board, score, high_score)
        wants_to_play = get_valid_answer()
        pygame.display.update()
    save_high_score(high_score)
    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            running = False
            pygame.quit()