为什么我的精灵没有在Pygame中绘制到屏幕上

我最近一直在尝试用python制作Snake游戏。该程序显示没有任何错误，但是当我运行该程序时，精灵不会绘制。我试着用Python运行这个程序，而不是在Visual Studio代码中运行，我试着更改Variables的名称，我也审查了很多次代码。请帮忙。

import pygame
import sys
import random
#Snake
class snake(object):
def __init__(self):
self.length = 1
self.positions = [((Screen_Width / 2), (Screen_Height / 2))]
self.direction = random.choice([Up, Down, Left, Right])
self.color = (0, 0, 0)
def head_position(self):
return self.positions[0]
def turn(self,point):
if self.length > 1 and (point[0] * -1, point[1] * -1) == self.direction:
return
else:
self.direction = point
def move(self):
cur = self.head_position()
x, y = self.direction
new = (((cur[0] + (x * Grid_Size)) % Screen_Width), (cur[1] + (y * Grid_Size)) % Screen_Height)
if len(self.positions) >2 and new in self.positions[2:]:
self.reset()
else:
self.positions.insert(0, new)
if len(self.positions) > self.length:
self.positions.pop()
def reset(self):
self.length = 1
self.positions = [((Screen_Width / 2), (Screen_Height / 2))]
self.direction = random.choice([Up, Down, Left, Right])
def draw(self, surface):
for p in self.positions:
r = pygame.Rect((p[0], p[1]), (Grid_Size, Grid_Size))
pygame.draw.rect(surface, self.color, r)
pygame.draw.rect(surface, (93, 216, 228), r, 1)
def handle_keys(self):
for event in pygame.event.get():
if event.type == pygame.QUIT:
pygame.quit()
sys.exit()
elif event.type == pygame.KEYDOWN:
if event.key == pygame.K_UP:
self.turn(Up)
elif event.key == pygame.K_DOWN:
self.turn(Down)
elif event.key == pygame.K_LEFT:
self.turn(Left)
if event.key == pygame.K_RIGHT:
self.turn(Right)

#Apple
class apple(object):

def __init__(self):
self.position = (0, 0)
self.color = (192, 7, 7)
self.randomize_position()
def randomize_position(self):
self.position = (random.randint(0, Grid_Width - 1) * Grid_Size, random.randint(0, Grid_Height -1) * Grid_Size)
def draw(self, surface):
r = pygame.Rect((self.position[0], self.position[1]), (Grid_Size, Grid_Size))
pygame.draw.rect(surface, self.color, r)
pygame.draw.rect(surface, (9, 196, 46), r, 1)
#Draw The Grid
def draw_grid(surface):
for y in range(0, int(Grid_Height)):
for x in range(0, int(Grid_Width)):
if (x + y) % 2 == 0:
r = pygame.Rect((x*Grid_Size, y*Grid_Size), (Grid_Size, Grid_Size))
pygame.draw.rect(surface, (9, 196, 46), r)
else:
rr = pygame.Rect((x*Grid_Size, y*Grid_Size), (Grid_Size, Grid_Size))
pygame.draw.rect(surface, (7, 138, 33), rr)

#Screen
Screen_Width = 500
Screen_Height = 500
Grid_Size = 20
Grid_Width = Screen_Height / Grid_Size
Grid_Height = Screen_Width / Grid_Size
#Movement
Up = (0, -1)
Down = (0, 1)
Left = (-1, 0)
Right = (1, 0)
#Main Game Loop
def Main():
pygame.init()
clock = pygame.time.Clock()
screen = pygame.display.set_mode((Screen_Width, Screen_Height), 0, 32)
surface = pygame.Surface(screen.get_size())
surface = surface.convert()
draw_grid(surface)
the_snake = snake()
food = apple()
my_font = pygame.font.SysFont("monospace", 16)
score = 0
#Handling Events.
while (True):
clock.tick(10)
the_snake.handle_keys()
draw_grid(surface)
the_snake.move()
if the_snake.head_position() == food.position:
snake.length += 1
score += 1
food.randomize_position()
screen.blit(surface, (0, 0))
text = my_font.render("Score {0}".format(score), 1, (0, 0, 0))
screen.blit(text, (5, 10))
pygame.display.update()
#Call On The Main Function.
Main()