My first snake game in pygame. Requires pygame 3.4 module.

slither.py

import pygame
import random

#Initialization
pygame.init()
print("> Snake Debug Console")
print("")

#Defining colors
white = (255,255,255)
black = (0,0,0)
red = (255,0,0) #RGB
green = (0,155,0)
blue = (0,0,255)
cyan = (0,220,220)

#Display
display_size = (800,600)
display_width = display_size[0]
display_height = display_size[1]
fps = 20
gameDisplay = pygame.display.set_mode(display_size)
clock = pygame.time.Clock()

title = "Slither! A Snake Game. Created by Vox"
pygame.display.set_caption(title)

pygame.display.update()

font_size = 30
font = pygame.font.SysFont(None, font_size)

##def main_menu():
##    menuExit = False
##    select = 0
##    
##    while not menuExit:
##        screen_text = font.render("Play", True, cyan)
##        pos_x=display_width/2
##        pos_y=display_height/2-200
##        gameDisplay.blit(screen_text, [pos_x,pos_y])
##        for event in pygame.event.get():
##            if event.type == pygame.KEYDOWN:
##                if event.key == pygame.K_UP: #Checkpoint! I'm here! Creating my main menu
                    
def snake(block_size, color, snakelist):
    for XnY in snakelist:
        pygame.draw.rect(gameDisplay, color, [XnY[0],XnY[1],block_size,block_size])


def message_to_screen(msg, color):
    screen_text = font.render(msg, True, color)
    pos_x=display_width/2-200
    pos_y=display_height/2
    gameDisplay.blit(screen_text, [pos_x,pos_y])


def gameLoop():
    
    #Game Loop
    gameExit = False
    gameOver = False
    
    #Defining Varibles (Trying to not hardcode)
    lead_x = display_width/2
    lead_y = display_height/2
    
    lead_x_change = 0
    lead_y_change = 0
    
    current_direction="none"
    block_size = 10
    lead_color=black
    snakeList = []
    snakeLength = 1
    score = 0
    move_speed = 10
    
    randAppleX = round(random.randrange(0+block_size, display_width-block_size)/10)*10
    randAppleY = round(random.randrange(0+block_size, display_height-block_size)/10)*10
    apple_size = 10
    
    while not gameExit: #Main Loop
        
        while gameOver == True:
            gameDisplay.fill(cyan)
            message_to_screen("You Lose! Press R to play again, or Q to quit.", red)
            score = 0
            pygame.display.update()

            for event in pygame.event.get():

                if event.type == pygame.QUIT:
                    pygame.quit()
                    quit()
                
                if event.type == pygame.KEYDOWN:
                    
                    if event.key == pygame.K_r:
                        gameLoop()
                        snakeLength = 0
                        print("Restarting Game!")
                        
                    if event.key == pygame.K_q:
                        print("Quiting Game!")
                        gameOver == False
                        gameExit == True

            
        for event in pygame.event.get():
            
            if event.type == pygame.QUIT:
                gameExit = True
                
            if event.type == pygame.KEYDOWN:
                
                if event.key == pygame.K_LEFT and current_direction != "right":
                    lead_x_change=0
                    lead_y_change=0
                    lead_x_change = -move_speed
                    current_direction="left"
                elif event.key == pygame.K_RIGHT and current_direction != "left":
                    lead_x_change=0
                    lead_y_change=0
                    lead_x_change = move_speed
                    current_direction="right"
                elif event.key == pygame.K_UP and current_direction != "down":
                    lead_x_change=0
                    lead_y_change=0
                    lead_y_change = -move_speed
                    current_direction="up"
                elif event.key == pygame.K_DOWN and current_direction != "up":
                    lead_x_change=0
                    lead_y_change=0
                    lead_y_change = move_speed
                    current_direction="down"
        
        #Game Over
        if lead_x >= display_size[0] or lead_x <= 0 or lead_y >= display_size[1] or lead_y <= 0:
            gameOver = True
            print("Game Over!")
                    
        lead_x += lead_x_change
        lead_y += lead_y_change

        #Drawing Objects
        gameDisplay.fill(cyan) #Drawing Background
        pygame.draw.rect(gameDisplay, red, [randAppleX, randAppleY,apple_size,apple_size]) #Drawing Apple
        
        #Snake
        snakeHead = []
        snakeHead.append(lead_x)
        snakeHead.append(lead_y)
        snakeList.append(snakeHead)
        if len(snakeList) > snakeLength:
            del snakeList[0]
            
        snake(block_size, lead_color, snakeList) #Calls snake function.

        #Score Text
        score_text = font.render("Score: "+str(score), True, green)
        text_pos_x=0
        text_pos_y=display_height-font_size
        gameDisplay.blit(score_text, [text_pos_x,text_pos_y])
        
        pygame.display.update() #Updates Game

        #Apple colison & scoring. with Colison System version 2.
        if lead_x >= randAppleX and lead_x <= randAppleX + apple_size - 1:
            if lead_y >= randAppleY and lead_y <= randAppleY + apple_size - 1:
                print("You ate an apple!")
                score += 1
                snakeLength+=3
                randAppleX = round(random.randrange(0+block_size, display_width-block_size)/10)*10
                randAppleY = round(random.randrange(0+block_size, display_height-block_size)/10)*10
        

        clock.tick(fps) #Limiting FPS.
        
    pygame.quit()
    quit()

gameLoop()