UFO Python Pygame

import os, sys, time, lzma, base64
import pygame

png =   b'/Td6WFoAAATm1rRGAgAhARYAAAB0L+Wj4ACxAKxdAESUBcR6J/b37omOUJCIs6rVUCYF0PNiLs+9xFYYB8Sul44ej\
        96b+oKBBOpaT6rxFLCiqvfumffQaGjsBfQNxri9WeZzMTUNcsqJcwfuA6GxOwip+wELqVu9pBSSaxEANipkUacT/ArD\
        ys+CZuPmU09pRgc6Ejm84LnSlyycN8atFjBfCpA/EpDZ4PjOIojaW5t18NqVRsCmxam6hM+az8qMx+3JsDIsxeiiz6A\
        AoFP90XGhYFkAAcgBsgEAAJKNN7WxxGf7AgAAAAAEWVo='

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

def loadnscale(scale, filename):
    i = pygame.image.load(filename)
    r = i.get_rect()
    ni = pygame.transform.scale(i, (r.w * scale, r.h * scale))
    return ni, ni.get_rect()

pygame.init()
PDR = pygame.Rect(0, 0, 1024, 800)
PDCENTER = pygame.math.Vector2(PDR.center)
PDS = pygame.display.set_mode(PDR.size)
FPS = 120

BLACK = (0, 0, 0)
SCALE = 4

ship_spritesheet, sss_rect = loadnscale(SCALE, "UFO.png")
ship_spritesheet.set_colorkey(BLACK)
ship_size = pygame.math.Vector2(sss_rect.midright)
ship_pos = pygame.math.Vector2(PDCENTER - ship_size / 2)
ship_sprites = [pygame.Rect((0, 0), ship_size), pygame.Rect((0, ship_size[1]), ship_size)]
ship_sprite_id = 0

gravity = 0.1
resistence = 0.05

velocity = pygame.math.Vector2()
max_velocity = 5
thrust = 0.2

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

    PDS.fill((0, 0, 0))
    PDS.blit(ship_spritesheet, ship_pos, ship_sprites[ship_sprite_id])


    pygame.display.update()

    ship_pos += velocity
    velocity += (0, gravity)

    if ship_pos[0] < -ship_size[0]:
        ship_pos[0] = PDR.right
    if ship_pos[0] > PDR.right:
        ship_pos[0] = -ship_size[0]
    if ship_pos[1] < -ship_size[1]:
        ship_pos[1] = PDR.bottom
    if ship_pos[1] > PDR.bottom:
        ship_pos[1] = -ship_size[1]

    k = pygame.key.get_pressed()
    if k[pygame.K_RIGHT]:
        velocity += (thrust, 0)
    elif k[pygame.K_LEFT]:
        velocity += (-thrust, 0)
    else:
        try:
            velocity[0] -= velocity[0] // abs(velocity[0]) * resistence
        except:
            pass

    if k[pygame.K_UP]:
        velocity += (0, -thrust)
        ship_sprite_id = 1
    else:
        ship_sprite_id = 0

    if velocity[0] > max_velocity or velocity[0] < -max_velocity:
        velocity[0] = velocity[0] // abs(velocity[0]) * max_velocity
    if velocity[1] > max_velocity or velocity[1] < -max_velocity:
        velocity[1] = velocity[1] // abs(velocity[1]) * max_velocity

    velocity[0] = round(velocity[0], 3)

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

pygame.quit()
sys.exit()