How to refresh the image content in a window?

edit

cv2.namedWindow("image",0)

img=cv2.imread("autojump.png")
while 1:
    img=cv2.imread("autojump.png")
    cv2.imshow("image",img)
    k=cv2.waitKey(0) & 0XFF
    if k== 27 :
        break
cv2.destroyAllWindows()

The image file autojump.png's content will change along with time(rewrited by with open("autojump.png","w" as f : f.write(some_other_image_bytes_stream)), so I reload it during the while loop, but it seems that the window never refresh.Just always the same image. What's wrong?