How can you add collision checking into this 2D cargame in the pygame module

Question

I am a beginner in Python and Pygame and i was hoping that someone could help me with implementing code that checks for collision between car and car2. I researched quite a bit for this but i wasn't able to implement the code into my project nor could i understand it. It would mean a lot if someone could help with this problem. I use Python 3.8.3.

Here is the code:

import pygame
import random
import math


pygame.init()


black = (0, 0, 0)

screen_width = 600
screen_length = 800
screen = pygame.display.set_mode((screen_length, screen_width))
clock = pygame.time.Clock()
FPS = 60

icon = pygame.image.load('car.png')
pygame.display.set_icon(icon)

#game caption
pygame.display.set_caption("Car game")




#Main car
car = pygame.image.load('car.png')
carX = 370
carY = 470 
carX_change = 0

#second car
car2 = pygame.image.load('car2.png')
car2_X = random.randint(200, 600)
car2_Y = random.randint(-50, 0)
car2Y_speed = 13


#road side trees
tree1Img = pygame.image.load('tree1.png')
tree1_X = 70
tree1_Y = 30

tree2Img = pygame.image.load("tree2.png")
tree2_X = 700
tree2_Y = 300


tree3Img = pygame.image.load("tree3.png")
tree3_X = 70
tree3_Y = 400

tree4Img = pygame.image.load("tree4.png")
tree4_X = 700
tree4_Y = 50



#game functions
def car1(x, y):
    screen.blit(car, (x, y))

def car_2(x, y):
    global car2_Y
    global car2_X
    screen.blit(car2, (x, y))
    car2_Y += car2Y_speed
    if car2_Y > screen_length:
        car2_X = random.randint(200, 545)
        car2_Y = random.randint(-50, 0)   


def tree1(x, y):
    global tree1_Y
    screen.blit(tree1Img, (x, y))
    tree1_Y += 10
    if tree1_Y >= screen_width:
        tree1_Y = -50


def tree2(x, y):
    global tree2_Y
    screen.blit(tree2Img, (x, y))
    tree2_Y += 10
    if tree2_Y >= screen_width:
        tree2_Y = -50


def tree3(x, y):
    global tree3_Y
    screen.blit(tree2Img, (x, y))
    tree3_Y += 10
    if tree3_Y >= screen_width:
        tree3_Y = -50


def tree4(x, y):
    global tree4_Y
    screen.blit(tree4Img, (x, y))
    tree4_Y += 10
    if tree4_Y >= screen_width:
        tree4_Y = -50

# 1st Road marker's movement
rectangleX = 426
rectangleY = 100
def roadmarker_move():
    global rectangleY
    if running == True:
        rectangleY += 10
    if rectangleY == 610:
        rectangleY = -50


#2nd road marker's movement
rectangle2_X = 426
rectangle2_Y = 410
def roadmarker2_move():
    global rectangle2_Y
    if running == True:
        rectangle2_Y += 10
    if rectangle2_Y == 610:
        rectangle2_Y = -50




#Main game loop
running = True
while running:
    screen.fill((119, 118, 110))
    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            running = False

        if event.type == pygame.KEYDOWN:
            if event.key == pygame.K_RIGHT:
                carX_change = 48
            if event.key == pygame.K_LEFT:
                carX_change = -48

        if event.type == pygame.KEYUP:
            if event.key == pygame.K_LEFT or event.key == pygame.K_RIGHT:
                carX_change = 0
        carX += carX_change



    #drawing Road lines
    pygame.draw.line(screen, black, (639, 0), (639, 600), 10)
    pygame.draw.line(screen, black, (200, 0), (200, 600), 10)

    
    #drawing the 1st road markers
    rectangle = pygame.draw.rect(screen, black, (rectangleX, rectangleY, 15, 80))
    roadmarker_move()

    #drawing the 2nd road markers
    rectangle = pygame.draw.rect(screen, black, (rectangle2_X, rectangle2_Y, 15, 80))
    roadmarker2_move()

    #setting boundries
    if carX <= 170:
        carX = 170
    elif carX >= 547:
        carX = 547




    car1(carX, carY)
    car_2(car2_X, car2_Y)
    tree1(tree1_X, tree1_Y)
    tree2(tree2_X, tree2_Y)
    tree3(tree3_X, tree3_Y)
    tree4(tree4_X, tree4_Y)
    clock.tick(FPS)
    pygame.display.update()

pygame.quit()

Answer 1

It's best to use PyGame's Rect class. It make handling these sorts of collisions quite simple.

Create a Rect for each object, and put your objects in a list:

#road side trees
tree1img  = pygame.image.load('tree1.png')
tree1rect = tree1img.get_rect()
tree1rect.topleft = (  70,  30 )

tree2img = pygame.image.load("tree2.png")
tree2rect = tree2img.get_rect()
tree2rect.topleft = ( 700, 300 )

tree3img = pygame.image.load("tree3.png")
tree3rect = tree3img.get_rect()
tree3rect.topleft = (  70, 400 )

tree4img = pygame.image.load("tree4.png")
tree4rect = tree4img.get_rect()
tree4rect.topleft = ( 700,  50 )

tree_images = [ tree1img, tree2img, tree3img, tree4img ]
tree_rects  = [ tree1rect, tree2rect, tree3rect, tree4rect ]

Similarly for Cars:

car = pygame.image.load('car.png')
car_rect = car.get_rect()
car_rect.topleft = ( 370, 470 )

When it's time time move the car, adjust the car_rect.

car_rect.move_ip( ( carX_change, 0 ) )

To draw the car, the blit can just use the rect too:

screen.blit( car, car_rect )

To check for collisions, use Rect.colliderect() or Rect.collidelist():

# did car hit a tree?
for tree_rect in tree_rects:
    if ( tree_rect.colliderect( car_rect ) ):
        print( "car hit tree" )

Or

# did car hit a tree:
if ( car_rect.collidelist( tree_rects ) ):
    print( "car hit tree" )

Pygame.Rect(), you know you want it ;)