python之PyGame 中康威的生命游戏没有生成正确的模式

我正在尝试使用 pygame 在 python 中制作康威的生活游戏。我不明白为什么，但它生成的模式已经偏离了。我已经查看了代码一百万次，但看不出有什么问题。

这是其中一代的截图

这是游戏的完整代码。

import pygame, sys 
from pygame.locals import * 
from random import randint 
import numpy 
 
#inititalize 
pygame.init() 
clock = pygame.time.Clock() 
 
#constants 
FPS = 10 
BLACK = (0,0,0) 
RED = (255,0,0) 
GREY = (30,30,30) 
SCREENX = 640 
SCREENY = 480 
CELLSIZE = 10 
HEIGHT = SCREENY/CELLSIZE 
WIDTH = SCREENX/CELLSIZE 
 
#set up window 
window = pygame.display.set_mode((SCREENX, SCREENY)) 
pygame.display.set_caption('Game of Life') 
window.fill(BLACK) 
 
#generate random seed 
cells = numpy.zeros((WIDTH,HEIGHT), dtype=numpy.int) 
for x in range(0,WIDTH): 
    for y in range(0,HEIGHT): 
        #0 is a dead cell, 1 is an alive cell 
        cells[x][y] = randint(0,1) 
 
def findNeighbors(grid, x, y): 
    if 0 < x < len(grid) - 1: 
        xi = (0, -1, 1) 
    elif x > 0: 
        xi = (0, -1) 
    else: 
        xi = (0, 1) 
 
    if 0 < y < len(grid[0]) - 1: 
        yi = (0, -1, 1) 
    elif y > 0: 
        yi = (0, -1) 
    else: 
        yi = (0, 1) 
 
    for a in xi: 
        for b in yi: 
            if a == b == 0: 
                continue 
            yield grid[x + a][y + b] 
 
def update(grid, x, y): 
    #determine num of living neighbors 
    neighbors = findNeighbors(cells,x,y) 
    alive = 0 
    for i in neighbors: 
        if i == 1: 
            alive+=1 
 
    #if current cell is alive 
    if grid[x][y] == 1: 
        #kill if less than 2 or more than 3 alive neighbors 
        if (alive < 2) or (alive > 3): 
            return 0 
        else: 
            return 1 
    #if current cell is dead 
    elif grid[x][y] == 0: 
        #make alive if 3 alive neighbors 
        if alive == 3: 
            return 1 
        else: 
            return 0 
 
#main loop 
while True: 
 
    #check if user wants to exit 
    for event in pygame.event.get(): 
        if event.type == pygame.QUIT: 
            pygame.quit() 
            sys.exit() 
 
    #update cells 
    for x in range(0,WIDTH): 
        for y in range(0,HEIGHT): 
            cells[x][y] = update(cells,x,y) 
 
    #draw grid 
    for x in range(0,SCREENX,CELLSIZE): 
        for y in range(0,SCREENY,CELLSIZE): 
            #if cell is alive 
            if cells[x/CELLSIZE][y/CELLSIZE] == 1: 
                #draw red square 
                pygame.draw.rect(window, RED, [x, y, CELLSIZE, CELLSIZE]) 
            else: 
                #draw black square 
                pygame.draw.rect(window, BLACK, [x, y, CELLSIZE, CELLSIZE]) 
            #draw square border 
            pygame.draw.rect(window, GREY, [x, y, CELLSIZE, CELLSIZE], 1) 
 
    #draw updates 
    pygame.display.update() 
 
    #generations per second 
    clock.tick(FPS) 

我不认为问题出在 findNeighbors 函数上，因为我是从 this 得到的计算器答案。所以我假设问题出在更新函数中，但我无法根据游戏规则看出逻辑错误的地方。