Pygame USB-serial keyboard control - Raspberry Pi to arduino

import pygame
import serial

ser = serial.Serial('/dev/ttyACM0', 9600)

# Define some colors
BLACK = (0, 0, 0)
WHITE = (255, 255, 255)
GREEN = (0, 255, 0)
RED = (255, 0, 0)


def draw_stick_figure(screen, x, y):
    # Head
    pygame.draw.ellipse(screen, BLACK, [1 + x, y, 10, 10], 0)



# Setup
pygame.init()

# Set the width and height of the screen [width,height]
size = [320, 240]
screen = pygame.display.set_mode(size)

pygame.display.set_caption("LunkVehikel Control Pannel")

# Loop until the user clicks the close button.
done = False

# Used to manage how fast the screen updates
clock = pygame.time.Clock()

# Hide the mouse cursor
pygame.mouse.set_visible(0)

# Speed in pixels per frame
x_speed = 0
y_speed = 0

# Current position
x_coord = 160
y_coord = 120

# -------- Main Program Loop -----------
while not done:
    # --- Event Processing
    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            done = True
            # User pressed down on a key

        elif event.type == pygame.KEYDOWN:
            # Figure out if it was an arrow key. If so
            # adjust speed.

            if event.key == pygame.K_KP4:
                x_speed = -3
                ser.write('4')

            elif event.key == pygame.K_KP6:
                x_speed = 3
                ser.write('6')

            elif event.key == pygame.K_KP8:
                y_speed = -3
                ser.write('8')

            elif event.key == pygame.K_KP2:
                y_speed = 3
                ser.write('2')


        # User let up on a key
        elif event.type == pygame.KEYUP:
            # If it is an arrow key, reset vector back to zero
            if event.key == pygame.K_KP4 or event.key == pygame.K_KP6:
                x_speed = 0
                ser.write('5')
            elif event.key == pygame.K_KP8 or event.key == pygame.K_KP2:
                y_speed = 0
                ser.write('7')

    # --- Game Logic

    # Move the object according to the speed vector.
    x_coord = x_coord + x_speed

    if x_coord > 320:
        x_coord = 1

    if x_coord < 0:
        x_coord = 319

    y_coord = y_coord + y_speed

    if y_coord > 240:
        y_coord = 1

    if y_coord < 0:
        y_coord = 239


    # --- Drawing Code

    # First, clear the screen to WHITE. Don't put other drawing commands
    # above this, or they will be erased with this command.
    screen.fill(WHITE)

    draw_stick_figure(screen, x_coord, y_coord)
    # draw_up_arrow(screen, 160, 120)


    # Go ahead and update the screen with what we've drawn.
    pygame.display.flip()

    # Limit frames per second
    clock.tick(60)

# Close the window and quit.
pygame.quit()