Very Simple Pong Game in Python using PyGame

import random

import pygame


pygame.init()
screen = pygame.display.set_mode( ( 640, 480 ) )
screen.fill( ( 255, 255, 255 ) )
balx, baly = ( 320, 240 )
balxspeed, balyspeed = random.choice( [( 1, 1 ), ( -1, 1 ), ( 1, -1 ), ( -1, -1 )] )
fps = pygame.time.Clock()
yleft = 240
yright = 240

right_score = 0
left_score = 0

while True:
    eventlst = pygame.event.get()
    for event in eventlst:
        if event.type == pygame.QUIT:
            raise SystemExit

    #  move the ball
    balx += balxspeed
    baly += balyspeed

    #  if the ball hits 0-up or 480-down it bounces back
    if baly >= 480 or baly <= 0:
        balyspeed *= -1

    #  score board
    if balx <= 0:
        right_score += 1
        #  print "left", left_score, "-", right_score, "right"
    if balx >= 640:
        left_score += 1
        #  print "left", left_score, "-", right_score, "right"

    #  if the ball hits 0-left or 640-right it resets the ball
    if balx >= 640 or balx <= 0:
        balx, baly = ( 320, 240 )
        balxspeed, balyspeed = random.choice( [( 1, 1 ), ( -1, 1 ), ( 1, -1 ), ( -1, -1 )] )

    keys = pygame.key.get_pressed()

    #  move the rectangle up or down
    if keys[pygame.K_DOWN]:
        yright += 2
    if keys[pygame.K_UP]:
        yright -= 2
    if keys[pygame.K_w]:
        yleft -= 2
    if keys[pygame.K_s]:
        yleft += 2

    #  make sure the rectangle yleft doesn't go further up or down than either 0 or 480
    if yleft <= 0:
        yleft = 0
    if yleft >= 430:
        yleft = 430
    #  make sure the rectangle yright doesn't go further up or down than either 0 or 480
    if yright <= 0:
        yright = 0
    if yright >= 430:
        yright = 430

    if balx <= 10:
        #  if ball hits rectangle do bounce
        if baly >= yleft and baly <= yleft + 50:
            balxspeed *= -1.5
            balx = 11
            if keys[pygame.K_w]:
                balyspeed = -abs( balyspeed )
            if keys[pygame.K_s]:
                balyspeed = abs( balyspeed )

    if balx >= 630:
        #  if ball hits rectangle do bounce
        if baly >= yright and baly <= yright + 50:
            balxspeed *= -1.5
            balx = 629
            if keys[pygame.K_UP]:
                balyspeed = -abs( balyspeed )
            if keys[pygame.K_DOWN]:
                balyspeed = abs( balyspeed )

    screen.fill( ( 255, 255, 255 ) )
    pygame.draw.circle( screen, ( 255, 0, 0 ), ( int( balx ), int( baly ) ), 8 )
    pygame.draw.rect( screen, ( 0, 0, 0 ), ( 0, yleft, 10, 50 ) )
    pygame.draw.rect( screen, ( 0, 0, 0 ), ( 630, yright, 10, 50 ) )
    pygame.display.update()
    fps.tick( 60 )