Spawning an alien to chase the player

I have just made a simple script which spawns an alien that chases the player. I want to move as much of the script into functions so as to minimize the amount of code, to make it run better when my game gets a lot bigger. I am new to functions and classes, and I want to know what can be turned into a class in another script and how to go about doing it. I do not want just code, I want to be able to understand what I'm doing with it as well.

```
import pygame, sys, random, time, math
from pygame.locals import *
pygame.init()

bifl = 'screeing.jpg'
milf = 'character.png'
alien = 'alien_1.png'

screen = pygame.display.set_mode((640, 480))
background = pygame.image.load(bifl).convert()
mouse_c = pygame.image.load(milf).convert_alpha()
nPc = pygame.image.load(alien).convert_alpha()

x, y = 0, 0
movex, movey = 0, 0

z, w = random.randint(10, 480), random.randint(10, 640)
movez, movew = 0, 0

while True:
for event in pygame.event.get():
if event.type == QUIT:
pygame.quit()
sys.exit()

if event.type == KEYDOWN:
if event.key == K_w:
movey = - 4
elif event.key == K_s:
movey = + 4
elif event.key == K_a:
movex = - 4
elif event.key == K_d:
movex = + 4

if event.type == KEYUP:
if event.key == K_w:
movey = 0
elif event.key == K_s:
movey = 0
elif event.key == K_a:
movex = 0
elif event.key == K_d:
movex = 0

if w x:
movew =- 0.4
if z y:
movez =- 0.4

x += movex
y += movey
w += movew
z += movez
print('charecter pos: ' + str(x) + str(y))
print('alien pos: ' + str(w) + str(z))

chpos = x + y
alpos = w + z
print(alpos, chpos)
if chpos == alpos:
pygame.quit()
sys.exit()

screen.blit(background, (0, 0))
screen.blit(mouse_c,

Long multiple choice decisions in python work well as dictionaries, rather than elifs.

def handle_event(event):
    OnKeyDown = {K_w:(0, 4), K_s:(0,-4), K_a:(-4, 0), K_d:(4,0)}
    OnKeyUp = {K_w:(False, True), K_s:(False, True), K_a:(True, False), K_d:(True, False)}

    if event.type == KEYUP:
         delta = OnKeyDown[event]
         movex += delta[0]
         movey += delta[1]
    elif event.type == KEYDOWN:
         delta = OnKeyUp[event]
         if delta[0]: movex = 0
         if delta[1]: movey = 0

   x += movex
   y += movey

StackExchange Code Review Q#31230, answer score: 3