How to set up co-ordinates correctly for my game

Question

How to make the red block appear between grey and green block.

In the above picture i changed my rectangle x position of donkey to 160 then only i can able to see the red block if not means i'll hide under grey block.

this is my code

class Road(pygame.sprite.Sprite):
    def __init__(self):
        pygame.sprite.Sprite.__init__(self)
        self.image = pygame.Surface((200, 500))
        self.image.fill(grey)
        self.rect = self.image.get_rect()
        self.rect.centerx = width/2
        #self.rect.left = width-200
        #print self.rect.left
        self.speedy = 5
    def update(self):
        self.rect.y += self.speedy
        if self.rect.y > 0:
            self.rect.y = 0

class Donkey(pygame.sprite.Sprite):
    def __init__(self):
        pygame.sprite.Sprite.__init__(self)
        self.image = pygame.Surface((100, 100))
        self.image.fill(red)
        self.rect = self.image.get_rect()
        self.rect.x = 200
        print 'x:',self.rect.x
        self.rect.y = -54
        print 'y:',self.rect.y
        self.speedy = random.randint(8,10)
    def update(self):
        self.choice = (200, 300)
        self.rect.y += self.speedy
        if self.rect.top > height:
            self.rect.x = random.choice(self.choice)
            print 'x:', self.rect.x
            self.rect.y = random.randrange(-100, -40)
            print 'y', self.rect.y
            self.speedy = random.randint(8,10)

class Race_car(pygame.sprite.Sprite):
    def __init__(self):
        pygame.sprite.Sprite.__init__(self)
        self.image = pygame.Surface((100, 100))
        self.image.fill(green)
        self.rect = self.image.get_rect()
        self.rect.x = 200
        self.rect.bottom = height
        self.speedy = -0.1
    def update(self):
        #self.speedx = 0
        self.rect.y += self.speedy
        keypressed = pygame.key.get_pressed()
        if keypressed[pygame.K_RIGHT]:
            self.rect.x = 300
        elif keypressed[pygame.K_LEFT]:
            self.rect.x = 200


#Group, object for game_hearth
game_hearth = pygame.sprite.Group()
road = Road()
game_hearth.add(road)

#Group, object for donkey
donkey = Donkey()
donkeys = pygame.sprite.Group()
game_hearth.add(donkey)
donkeys.add(donkey)

#Group, object for racecar
racecar = Race_car()
racecars = pygame.sprite.Group()
game_hearth.add(racecar)
racecars.add(racecar)

when i run my code after commenting the Race_car class the red blocks working fine, see

so the thing is i want to display the both red and green block above the grey road. so how to do it without commenting any class in my program. i know its some co-ordinate mistake but i don't know where to change it.

Answer 1

From the Pygame docs :

The Group does not keep sprites in any order, so the draw order is arbitrary.

You should probably switch to pygame.sprite.OrderedUpdates :

This class derives from pygame.sprite.RenderUpdates(). It maintains the order in which the Sprites were added to the Group for rendering. This makes adding and removing Sprites from the Group a little slower than regular Groups.

#Group, object for game_hearth
game_hearth = pygame.sprite.OrderedUpdates()

road = Road()
game_hearth.add(road)

#Group, object for donkey
donkey = Donkey()
donkeys = pygame.sprite.OrderedUpdates()
game_hearth.add(donkey)
donkeys.add(donkey)

#Group, object for racecar
racecar = Race_car()
racecars = pygame.sprite.OrderedUpdates()
game_hearth.add(racecar)
racecars.add(racecar)