2 players control 2 cars and try to avoid colissions

2_cars_pygame.py

# http://richard.cgpublisher.com/product/pub.84/prod.11
# INTIALISATION
import pygame, math, sys, random
from pygame.locals import *

TURN_SPEED = 5
ACCELERATION = 2
MAX_FORWARD_SPEED = 10
MAX_REVERSE_SPEED = 5
BG= (0,0,0)
MAX_Y = 768
MAX_X = 1024
COLLISION_DISTANCE = (MAX_Y*10)

def check_speed(speed):
    if speed > MAX_FORWARD_SPEED:
        speed = MAX_FORWARD_SPEED
    if speed < MAX_REVERSE_SPEED:
        speed = MAX_REVERSE_SPEED
    return speed

def check_direction(direction):
    return direction % 360

def is_collision(pos1, pos2):
    distance = (pos1[0]-pos2[0])**2+(pos1[1]-pos2[1])**2
    print distance
    return distance<COLLISION_DISTANCE

def main():
    # initialize the screen with size (MAX_X, MAX_Y)
    screen = pygame.display.set_mode((MAX_X, MAX_Y))
    num_cars = 2
    # load picture file - Car: http://www.xnadevelopment.com/tutorials/introducingxnagamestudioexpress/Car.png 
    car = []
    while len(car)<num_cars:
        car.append(pygame.image.load('car.png'))
        car.append(pygame.image.load('car2.png'))
    # initialize the sound mixer
    pygame.mixer.init()
    # load horn sound http://www.freesound.org/people/KRAFTWERK2K1/sounds/32417/
    horn = pygame.mixer.Sound('car-horn.wav') 
    clock = pygame.time.Clock() # load clock
    k_up = k_down = k_left = k_right = k_c = k_z = k_s = k_x = 0 # init key values
    # start speed, direction & position
    speed = [0]*num_cars 
    direction = [0]*num_cars
    position = [(100, 100)]*num_cars

    play = True
    while play:
        # USER INPUT
        clock.tick(30)
        # get events from the user
        for event in pygame.event.get():
            # not a key event
            if not hasattr(event, 'key'):
                continue
            # check if presses a key or left it
            down = event.type == KEYDOWN # key down or up?        
            # key events: http://pygame.org/docs/ref/key.html
            if event.key == K_RIGHT:
                k_right = down * TURN_SPEED
            elif event.key == K_LEFT:
                k_left = down * TURN_SPEED
            elif event.key == K_UP:
                k_up = down * ACCELERATION
            elif event.key == K_DOWN:
                k_down = down * ACCELERATION
            if event.key == K_c:
                k_c = down * TURN_SPEED
            elif event.key == K_z:
                k_z = down * TURN_SPEED
            elif event.key == K_s:
                k_s = down * ACCELERATION
            elif event.key == K_x:
                k_x = down * ACCELERATION
            elif event.key == K_RETURN:
                horn.play() 
            elif event.key == K_ESCAPE:
                play = False

        speed[0] += (k_up - k_down)    
        speed[0] = check_speed(speed[0])
        direction[0] += (k_left - k_right)
        direction[0] = check_direction(direction[0])
        speed[1] += (k_s - k_x)    
        speed[1] = check_speed(speed[1])
        direction[1] += (k_z - k_c)
        direction[1] = check_direction(direction[1])
          
        screen.fill(BG)
        
        for j in range(num_cars):    
            x, y = position[j]
            rad = direction[j] * math.pi / 180
            x += speed[j]*math.sin(rad)
            y += speed[j]*math.cos(rad)
            # make sure the car doesn't exit the screen
            if y < 0:
                y = MAX_Y 
            elif y > MAX_Y:
                y = 0
            if x < 0:
                x = MAX_X
            elif x > MAX_X:
                x = 0       
            position[j] = (x, y)
            # RENDERING
            # .. rotate the car image for direction
            rotated = pygame.transform.rotate(car[j], direction[j])
            # .. position the car on screen
            rect = rotated.get_rect()
            rect.center = position[j]    
            # .. render the car to screen
            screen.blit(rotated, rect)
        if is_collision(position[0],position[1]):
            horn.play()
        pygame.display.flip()

    sys.exit(0) # quit the game

if __name__=='__main__':
    main()