This python code allows the snake to grow a tail segment each time it eats food.

Snake with growing tail

from pyglet import app
from pyglet import gl
from pyglet import clock
from pyglet.window import Window
from pyglet.window import key
from pyglet import graphics
from pyglet import image
from pyglet import text
from random import randint
import sys

window = Window(500, 500)
@window.event
def on_draw():
    global snk_x, snk_y 
    if not game_over:
        window.clear()
        for coords in tail:
            draw_square(coords[0], coords[1], snk_size, colour = (255, 0, 255, 0))  #add tail
        draw_square(snk_x, snk_y, snk_size)      # Draw the snake's head.
        draw_square(fd_x, fd_y, snk_size, colour = (0, 255, 0, 0))  #draw food
    else:
        draw_game_over()
    
def draw_square(x, y, size, colour = (255, 255, 255, 0)):
    img = image.create(size, size, image.SolidColorImagePattern(colour))
    img.blit(x, y)
    
def place_food():
    global fd_x, fd_y
    fd_x = randint(0, (window.width // snk_size)-1) * snk_size
    fd_y = randint(0, (window.height // snk_size)-1) * snk_size

@window.event
def on_key_press(symbol, modifiers):
    global snk_dx, snk_dy, app
    if not game_over:
        if symbol == key.LEFT:
            snk_dx = -snk_size
            snk_dy = 0
        elif symbol == key.RIGHT:
            snk_dx = snk_size
            snk_dy = 0
        elif symbol == key.UP:
            snk_dx = 0
            snk_dy = snk_size
        elif symbol == key.DOWN:
            snk_dx = 0
            snk_dy = -snk_size

def update(dt):
    global snk_x, snk_y, snk_dx, snk_dy, snk_size, app, game_over, window, score   
    if snk_x + snk_dx < 0 or snk_x + snk_dx > window.width or snk_y + snk_dy < 0 or snk_y + snk_dy > window.height:     # Check for collision with edge.
       game_over = True
       app.exit()
       window.close()
       return  
  
    tail.append((snk_x, snk_y))  #add position of head to tail
  
    snk_x += snk_dx
    snk_y += snk_dy

    if snk_x == fd_x and snk_y == fd_y:
        print('yay!')
        place_food()
        score += 1
        print(f'Your score is {score}.')
        #don't remove last tail segment, hence we grow
    else:
        tail.pop(0)  #remove last tail segment
    print(tail)
score = 0
snk_size = 20 # Not the length of the snake, but the width and height of a single snake segment.
snk_dx, snk_dy = 0, 0 # The amount by which the snake's x and y coordinates change.
fd_x, fd_y = 0, 0  #defining food variables

snk_x = window.width // snk_size // 2 * snk_size  # Start the snake in the middle, ensuring that it doesn't land between cells.
snk_y = window.height // snk_size // 2 * snk_size
place_food()
game_over = False
tail = []
clock.schedule_interval(update, 1/15)  # Set how often the update function is called.
app.run()  # Start the game.