PyGame get sprite group

hey guys, was trying to build pacman using pygame, have a small problem. When the pacman is moving if i press a key the开发者_如何学运维n it changes direction, unfortunately if there is a wall above then the pacman stops at that place and points upwards until i change the direction. I want help with how to find out if the block 3 or 4 units of pacman.rect.y belongs to sprite group level which has all the walls and stuff ..

Here's a longer example of a working game with walls:

# Sample Python/Pygame Programs
# Simpson College Computer Science
# http://cs.simpson.edu/?q=python_pygame_examples

import pygame

black = (0,0,0)
white = (255,255,255)
blue = (0,0,255)

# This class represents the bar at the bottom that the player controls
class Wall(pygame.sprite.Sprite):
    # Constructor function
    def __init__(self,x,y,width,height):
        # Call the parent's constructor
        pygame.sprite.Sprite.__init__(self)

        # Make a blue wall, of the size specified in the parameters
        self.image = pygame.Surface([width, height])
        self.image.fill(blue)

        # Make our top-left corner the passed-in location.
        self.rect = self.image.get_rect()
        self.rect.top = y
        self.rect.left = x


# This class represents the bar at the bottom that the player controls
class Player(pygame.sprite.Sprite):

    # Set speed vector
    change_x=0
    change_y=0

    # Constructor function
    def __init__(self,x,y):
        # Call the parent's constructor
        pygame.sprite.Sprite.__init__(self)

        # Set height, width
        self.image = pygame.Surface([15, 15])
        self.image.fill(white)

        # Make our top-left corner the passed-in location.
        self.rect = self.image.get_rect()
        self.rect.top = y
        self.rect.left = x

    # Change the speed of the player
    def changespeed(self,x,y):
        self.change_x+=x
        self.change_y+=y

    # Find a new position for the player
    def update(self,walls):
        # Get the old position, in case we need to go back to it
        old_x=self.rect.left
        new_x=old_x+self.change_x
        self.rect.left = new_x

        # Did this update cause us to hit a wall?
        collide = pygame.sprite.spritecollide(self, walls, False)
        if collide:
            # Whoops, hit a wall. Go back to the old position
            self.rect.left=old_x

        old_y=self.rect.top
        new_y=old_y+self.change_y
        self.rect.top = new_y

        # Did this update cause us to hit a wall?
        collide = pygame.sprite.spritecollide(self, walls, False)
        if collide:
            # Whoops, hit a wall. Go back to the old position
            self.rect.top=old_y


score = 0
# Call this function so the Pygame library can initialize itself
pygame.init()

# Create an 800x600 sized screen
screen = pygame.display.set_mode([800, 600])

# Set the title of the window
pygame.display.set_caption('Test')

# Create a surface we can draw on
background = pygame.Surface(screen.get_size())

# Used for converting color maps and such
background = background.convert()

# Fill the screen with a black background
background.fill(black)

# Create the player paddle object
player = Player( 50,50 )
movingsprites = pygame.sprite.RenderPlain()
movingsprites.add(player)

# Make the walls. (x_pos, y_pos, width, height)
wall_list=pygame.sprite.RenderPlain()
wall=Wall(0,0,10,600)
wall_list.add(wall)
wall=Wall(10,0,790,10)
wall_list.add(wall)
wall=Wall(10,200,100,10)
wall_list.add(wall)

clock = pygame.time.Clock()

done = False

while done == False:

    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            done=True

        if event.type == pygame.KEYDOWN:
            if event.key == pygame.K_LEFT:
                player.changespeed(-3,0)
            if event.key == pygame.K_RIGHT:
                player.changespeed(3,0)
            if event.key == pygame.K_UP:
                player.changespeed(0,-3)
            if event.key == pygame.K_DOWN:
                player.changespeed(0,3)

        if event.type == pygame.KEYUP:
            if event.key == pygame.K_LEFT:
                player.changespeed(3,0)
            if event.key == pygame.K_RIGHT:
                player.changespeed(-3,0)
            if event.key == pygame.K_UP:
                player.changespeed(0,3)
            if event.key == pygame.K_DOWN:
                player.changespeed(0,-3)

    player.update(wall_list)

    screen.fill(black)

    movingsprites.draw(screen)
    wall_list.draw(screen)
    pygame.display.flip()

    clock.tick(40)

pygame.quit()

You could use: http://www.pygame.org/docs/ref/sprite.html#pygame.sprite.spritecollide

pacman.rect.y = pacman.rect.y - 3  
colliding = pygame.sprite.spritecollide(pacman, level)  
if colliding:
   can_move_upwards = False
else:
   can_move_upwards = True
pacman.rect.y = pacman.rect.y + 3

And do the same for every direction you want to test.