Group has no attribute rect and i dont know what to do

Question

I'm trying to program a traffic simulation and need the pygame collision detection. However as soon as i run the program (it isn't finished yet) it tells me i have an attribute error on car_up because it hasn't got the attribute rect. Can someone tell me why it is so and what i can do to improve it? And yes i have been trying figuring it out on my own but with no success.

import pygame
import random
import threading


from pygame.locals import (QUIT, KEYDOWN, K_ESCAPE)

# Define constants for the screen width and height
SCREEN_WIDTH = 1500
SCREEN_HEIGHT = 400
grey=[90 , 90 , 90]
green =[125, 255, 50]
spawnrate_up=1500
spawnrate_down=800
dimentions=[75,35]



#CLASSES

#create car
class Car_up (pygame.sprite.Sprite):
    def __init__(self, green, dimentions):
        # Call the parent class (Sprite) constructor
        pygame.sprite.Sprite.__init__(self)

        # Create an image of the block, and fill it with a color.
        # This could also be an image loaded from the disk.
        self.image = pygame.Surface(dimentions)
        self.image.fill(green)

        # Fetch the rectangle object that has the dimensions of the image
        # Update the position of this object by setting the values of rect.x and rect.y
        self.rect = self.image.get_rect()
        self.rect.x = random.randint(-100, -20)
        self.rect.y = 150

        self.speedx= 10
        self.speedy= 0
    # move car and delete once out of screen
    def update(self):
        merge=random.randint(750,1000)
        if self.rect.left > SCREEN_WIDTH:
            self.kill()
        if self.rect.colliderect(car_down.rect):
            car_up.speed.x=car_up.speed.y=0
        elif self.rect.centery<=266 and self.rect.centerx>merge:
            self.speedx=10
            self.speedy=3
        else:
            self.speedx=10
            self.speedy=0
        self.rect.move_ip(self.speedx, self.speedy)


class Car_down(pygame.sprite.Sprite):
    def __init__(self, green, dimentions):
        # Call the parent class (Sprite) constructor
        pygame.sprite.Sprite.__init__(self)

        # Create an image of the block, and fill it with a color.
        # This could also be an image loaded from the disk.
        self.image = pygame.Surface(dimentions)
        self.image.fill(green)


        # Fetch the rectangle object that has the dimensions of the image
        # Update the position of this object by setting the values of rect.x and rect.y
        self.rect = self.image.get_rect()
        self.rect.x = random.randint(-100,-20)
        self.rect.y = 250

        self.speedx= 10
        self.speedy= 0
    # move car and delete once out of screen
    def update(self):


        self.speedx=10
        self.speedy=0
        self.rect.move_ip(self.speedx, self.speedy)
        if self.rect.left > SCREEN_WIDTH:
            self.kill()

pygame.init()

# The size is determined by the constant SCREEN_WIDTH and SCREEN_HEIGHT
screen = pygame.display.set_mode((SCREEN_WIDTH, SCREEN_HEIGHT))
clock=pygame.time.Clock()
#create custom event
ADDCAR_down= pygame.USEREVENT + 1
ADDCAR_up= pygame.USEREVENT + 2
pygame.time.set_timer(ADDCAR_up, spawnrate_up )
pygame.time.set_timer(ADDCAR_down, spawnrate_down )

#create car

car_up= pygame.sprite.Group()
car_down= pygame.sprite.Group()
car_down.add(Car_down(green,dimentions))
car_up.add(Car_up(green,dimentions))

#infinite loop
run = True

#MAIN

while run:

    # Look at every event in the queue
    for event in pygame.event.get():
    # Did the user hit a key?
        if event.type == KEYDOWN:
            # Was it the Escape key? If so, stop the loop.
            if event.key == K_ESCAPE:
                run = False


        # Did the user click the window close button? If so, stop the loop.

        elif event.type == QUIT:
            run = False

        elif event.type == ADDCAR_down:
        # Create the new CAR and add it to sprite groups
            new_car_down = Car_down(green,dimentions)
            car_down.add(new_car_down)

        elif event.type == ADDCAR_up:
            new_car_up = Car_up(green,dimentions)
            car_up.add(new_car_up)


    #grey screen
    screen.fill(grey)

    # Draw the car on the screen

    car_up.draw(screen)
    car_up.update()
    car_down.draw(screen)
    car_down.update()

    pygame.display.flip()
    clock.tick(25)

Answer 1

car_down is apygame.sprite.Group so obviously it doesn't have a rect attribute. However the pygams.sprites.Sprite object in the Group have a rect attribute. You need to use pygame.sprite.spritecollide to detect collision of a Sprite and the objects in a Group :

if self.rect.colliderect(car_down.rect):

if pygame.sprite.spritecollide(self, car_down, False):   

See also How do I detect collision in pygame?