starting point for snake game lecture

snake_pygame_lecture.py

# Python 2.7
# Objectives: modules, game surface, Frames/sec (FPS), "skeleton" of a game, game loop, color, 
# setting object size, random, lists

# Rather than typing from scratch (only ~50min of lecture available), students will 
# each have these lines of code for a basic snake game using pygame.
# Lines will either be omitted or commented out
# students will follow along via the instructor/whiteboard; either typing in a few lines of code where its needed
# and/or students will uncomment lines of code that carry out specific feature related to the objectives

# BASIC SNAKE GAME
import pygame
import time
import random

pygame.init() # kicks pygame module off

# Specifying colors:
black = (0, 0, 0)          
white = (255, 255, 255)
red = (255, 0, 0)
green = (0, 180, 0)

# SETTING THE DIMENSIONS OF THE GAME WINDOW
display_width = 800
display_height = 600

gameDisplay = pygame.display.set_mode((display_width, display_height))
pygame.display.set_caption('Slither')

clock = pygame.time.Clock()

block_size = 10

# SETTING MOVEMENT SPEED (frames per second):
FPS = 30

font = pygame.font.SysFont(None, 25) 

# Defining snake function:
def snake(block_size, snakeList):
    for XnY in snakeList: # starting the growing of the snake
        pygame.draw.rect(gameDisplay, green, [XnY[0], XnY[1], block_size, block_size])
    
def message_to_screen(msg,color):
    screen_text = font.render(msg, True, color)
    gameDisplay.blit(screen_text, [display_width/2, display_height/2])

# THE MAIN GAME LOOP:
def gameLoop():
    gameEXIT = False
    gameOver = False

    lead_x = display_width/2
    lead_y = display_height/2

    lead_x_change = 0
    lead_y_change = 0

    snakeList = []
    snakeLength = 1 # adding 1 to length of snake

# RANDOM SPAWN POINTS FOR APPLE:
    randAppleX = round(random.randrange(0, display_width - block_size)/10.0)*10.0
    randAppleY = round(random.randrange(0, display_height - block_size)/10.0)*10.0
    
    while not gameEXIT:

        while gameOver == True:
            gameDisplay.fill(white)
            message_to_screen("Game over, press C to play again or Q to quit", red)
            pygame.display.update()

            for event in pygame.event.get():
                if event.type == pygame.KEYDOWN:
                    if event.key == pygame.K_q:
                        gameExit = True
                        gameOver = False
                    if event.key == pygame.K_c:
                        gameLoop()
                        
# RECOGNIZING KEYBOARD PRESSES FROM USER
# when the user presses a certain key, something specific happens
# (this is an event or conditions statements
        for event in pygame.event.get():
            if event.type == pygame.QUIT:
                gameEXIT = True
            if event.type == pygame.KEYDOWN:
                if event.key == pygame.K_LEFT: 
                    lead_x_change = -block_size
                    lead_y_change = 0
                elif event.key == pygame.K_RIGHT:
                    lead_x_change = block_size
                    lead_y_change = 0
                elif event.key == pygame.K_UP: 
                    lead_y_change = -block_size
                    lead_x_change = 0
                elif event.key == pygame.K_DOWN:
                    lead_y_change = block_size
                    lead_x_change = 0

    # BOUNDARIES:
        if lead_x >= display_width or lead_x < 0 or lead_y >= display_height or lead_y < 0:
                gameOver = True

    # LOGIC LOOP:
        lead_x += lead_x_change
        lead_y += lead_y_change
        
        gameDisplay.fill(white)
        pygame.draw.rect(gameDisplay, red, [randAppleX, randAppleY, block_size, block_size])

    # SNAKE GROWTH:
    # essentially adding to the snake block list
        snakeHead = []
        snakeHead.append(lead_x)
        snakeHead.append(lead_y)
        snakeList.append(snakeHead)

        if len(snakeList) > snakeLength:
            del snakeList[0]

        for eachSegment in snakeList[:-1]:
            if eachSegment == snakeHead:
                gameOver = True
 
        snake(block_size, snakeList)
# UPDATES YOUR CHANGES
        pygame.display.update()
        
    # EVENT FOR SNAKE/APPLE COLLISION:
        if lead_x == randAppleX and lead_y == randAppleY:
            randAppleX = round(random.randrange(0, display_width - block_size)/10.0)*10.0
            randAppleY = round(random.randrange(0, display_height - block_size)/10.0)*10.0
            snakeLength += 1

        clock.tick(FPS)

    pygame.quit()
    quit()
    
gameLoop()