pygame window at center

    pos_x = screen_width / 2 - window_width / 2
    pos_y = screen_height - window_height
    os.environ['SDL_VIDEO_WINDOW_POS'] = '%i,%i' % (pos_x,pos_y)
    os.environ['SDL_VIDEO_CENTERED'] = '0'

import pygame, os
os.environ['SDL_VIDEO_CENTERED'] = '1'

# This has to be done before you initialise pygame with pygame.init()