```"""
Simple snake example.

Sample Python/Pygame Programs
Simpson College Computer Science
http://simpson.edu/computer-science/

"""

import pygame

# --- Globals ---
# Colors
BLACK = (0, 0, 0)
WHITE = (255, 255, 255)

# Set the width and height of each snake segment
segment_width = 15
segment_height = 15
# Margin between each segment
segment_margin = 3

# Set initial speed
x_change = segment_width + segment_margin
y_change = 0

class Segment(pygame.sprite.Sprite):
""" Class to represent one segment of the snake. """
# -- Methods
# Constructor function
def __init__(self, x, y):
# Call the parent's constructor
super().__init__()

# Set height, width
self.image = pygame.Surface([segment_width, segment_height])
self.image.fill(WHITE)

# Make our top-left corner the passed-in location.
self.rect = self.image.get_rect()
self.rect.x = x
self.rect.y = y

# Call this function so the Pygame library can initialize itself
pygame.init()

# Create an 800x600 sized screen
screen = pygame.display.set_mode([800, 600])

# Set the title of the window
pygame.display.set_caption('Snake Example')

allspriteslist = pygame.sprite.Group()

# Create an initial snake
snake_segments = []
for i in range(15):
x = 250 - (segment_width + segment_margin) * i
y = 30
segment = Segment(x, y)
snake_segments.append(segment)

clock = pygame.time.Clock()
done = False

while not done:

for event in pygame.event.get():
if event.type == pygame.QUIT:
done = True

# Set the speed based on the key pressed
# We want the speed to be enough that we move a full
# segment, plus the margin.
if event.type == pygame.KEYDOWN:
if event.key == pygame.K_LEFT:
x_change = (segment_width + segment_margin) * -1
y_change = 0
if event.key == pygame.K_RIGHT:
x_change = (segment_width + segment_margin)
y_change = 0
if event.key == pygame.K_UP:
x_change = 0
y_change = (segment_height + segment_margin) * -1
if event.key == pygame.K_DOWN:
x_change = 0
y_change = (segment_height + segment_margin)

# Get rid of last segment of the snake
# .pop() command removes last item in list
old_segment = snake_segments.pop()
allspriteslist.remove(old_segment)

# Figure out where new segment will be
x = snake_segments.rect.x + x_change
y = snake_segments.rect.y + y_change
segment = Segment(x, y)

# Insert new segment into the list
snake_segments.insert(0, segment)

# -- Draw everything
# Clear screen
screen.fill(BLACK)

allspriteslist.draw(screen)

# Flip screen
pygame.display.flip()

# Pause
clock.tick(5)

pygame.quit()

```
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