Bouncing Title Cubes - Python Pygame

import sys, os.path
import base64, lzma, random
import pygame

titleZIP = b'/Td6WFoAAATm1rRGAgAhARYAAAB0L+WjAQELiVBORw0KGgoAAAANSUhEUgAAAEIAAAALBAMAAAA5LUZ\
AAAABGdBTUEAALGPC/xhBQAAAAFzUkdCAK7OHOkAAAAPUExURQAAANuqAbxYIaqFBP///5E0qmAAAACbSURBVBjTdY6B\
DcQgCEU/7QISFzBOYGIHuP2nugfaNrnkiH7o50mRu8tcqoVUJXkR1aAYollDLkFcWFQoYvWT925WWVlCWKlrRlwPx+NY\
oZ2flB4E3m2tLdy0CY9FAvMg3LegSeQz+yHmZG2dyMw0CfIc45xhST1nH42qkY5OYB6dcjVfAgci0H+EeL2I1hPv2gMf\
gj+0vgk9xBdehhKMcdGEzAAAAABJRU5ErkJgggCQOMXDkH/P4wABpAKMAgAAqAkTn7HEZ/sCAAAAAARZWg=='

if not os.path.exists("pygame.png"):
    print("Writing title image...", end = "")
    data = lzma.decompress(base64.b64decode(titleZIP))
    r = open("pygame.png", "bw")
    r.write(data)
    r.close()
    print("Done!")

pygame.init()
PDR = pygame.Rect(0, 0, 1280, 720)
PDS = pygame.display.set_mode(PDR.size)
FPS = 120

GRAVITY = 0.1
CUBE_DIMENSIONS = pygame.Rect(0, 0, 10, 10)
TIMER = FPS / 2

class drop:
    class cube:
        def __init__(s, color, x, floor):
            global CUBE_DIMENSIONS
            s.floor = floor * CUBE_DIMENSIONS.h
            s.speed = 0
            s.prevImpactSpeed = 0
            s.r = pygame.Rect((x * CUBE_DIMENSIONS.w, -CUBE_DIMENSIONS.h), CUBE_DIMENSIONS.size)
            s.color = color

    class column:
        def __init__(s):
            global CUBE_DIMENSIONS, TIMER
            s.cubes = []
            s.timer = random.randint(0, TIMER)

    def __init__(s, imageSurface):
        global PDS, PDR
        global CUBE_DIMENSIONS

        s.r = imageSurface.get_rect()
        cx = int(PDR.w / CUBE_DIMENSIONS.w) / 2 - s.r.centerx
        cy = int(PDR.h / CUBE_DIMENSIONS.h) / 2 - s.r.centery
        s.statics = []
        pa = pygame.PixelArray(imageSurface)

        s.columns = []
        for x in range(s.r.w):
            s.columns.append(s.column())
            for y in range(s.r.h):
                if pa[x][y] != 0: #16777215 (white)
                    s.columns[x].cubes.append(s.cube(PDS.unmap_rgb(pa[x][y]), cx + x, cy + y))
        pa.close()

    def do(s):
        global PDS, GRAVITY, TIMER

        for static in s.statics:
            pygame.draw.rect(PDS, static.color, static.r)

        for c in s.columns:

            if not c.cubes: continue
            if c.timer:
                c.timer -= 1
                continue

            currentCube = c.cubes[-1]
            pygame.draw.rect(PDS, currentCube.color, currentCube.r)

            currentCube.r.y += currentCube.speed
            currentCube.speed += GRAVITY
            if currentCube.r.bottom >= currentCube.floor:
                currentCube.r.bottom = currentCube.floor
                if currentCube.prevImpactSpeed == 0:
                    currentCube.prevImpactSpeed = currentCube.speed
                currentCube.prevImpactSpeed /= 3
                currentCube.speed = -currentCube.prevImpactSpeed
                if currentCube.prevImpactSpeed <= 0.5:
                    s.statics.append(c.cubes.pop(-1))
                    c.timer = random.randint(0, TIMER)

c = drop(pygame.image.load("pygame.png").convert())

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

    PDS.fill((0, 0, 0))

    c.do()

    pygame.display.update()
    pygame.time.Clock().tick(FPS)

pygame.quit()
sys.exit()