python - pygame crash right after taking an action -

im new @ python, problem @ code silly one. right after image of player moving, window of pygame crashing without error message @ idle.

im using python 2.7. here's code:

import pygame,sys pygame.locals import *  pygame.init() dis=pygame.display.set_mode((1084,638),0,32) pygame.display.set_caption('ledders , snakes')  fps=30 fpsclock=pygame.time.clock() white=(255,255,255) img=pygame.image.load('smal.gif') bg = pygame.image.load("under.gif")  cax=150 cay=150 di='right' flag=true  while flag:     dis.blit(bg, (0, 0))     if di=='right':         cax+=10         cay-=10         if cax==280:             di='down'     elif di=='down':         cay+=10         cax+=10         if cax==410:             flag=false       dis.blit(img,(cax,cay))      event in pygame.event.get():         if event.type==quit:             pygame.quit()             sys.exit()      pygame.display.update()     fpsclock.tick(fps) 

i through program , issue set flag = false when if cax == 410. why program quits, because condition becomes true after couple of seconds. there many things should consider, made changes (not in program in names):

import pygame import sys pygame.locals import *  pygame.init() size = width, height = 1084, 638  # have reference width , height. screen = pygame.display.set_mode(size, 0, 32)  # 'screen' convention , describes variable better 'dis'. pygame.display.set_caption('ledders , snakes')  fps = 30 clock = pygame.time.clock()  # use lowercase variables. white = (255, 255, 255)  # use caps constants. img = pygame.surface((32, 32))  # used these 2 lines because don't have image. img.fill((0, 0, 255)) bg = pygame.surface((32, 32))    # used these 2 lines because don't have image. bg.fill((255, 0, 0))  cax = 150  # since don't know program can't tell if these describable variables or not.  cay = 150 direction = 'right'  # 'di' isn't describable enough. running = true  # 'flag' seems indescribable variable.  while running:     screen.blit(bg, (0, 0))     if direction == 'right':         cax += 10         cay -= 10         if cax == 280:             direction = 'down'     elif direction == 'down':         cay += 10         cax += 10         if cax == 410:             running = false      screen.blit(img, (cax, cay))      event in pygame.event.get():         if event.type == quit:             pygame.quit()             sys.exit()      pygame.display.update()     clock.tick(fps) 

also, put spaces between operators ´==´ or after commas such ´(0, 0)´instead of (0,0). , use variable names lowercase, words separated underscore. try follow pep8, long doesn't make sense break it.