Cannot get continuous images using cv2.imshow()

I’m learning the code from https://pythonprogramming.net/reinforcement-learning-self-driving-autonomous-cars-carla-python/ , but i cannot get continuous images using cv2.imshow(), the dynamic picture last for less than 1 sec then it presents only static picture, i wonder if it is the problem of graphic ram, thank you so much in advance.QQ%E6%88%AA%E5%9B%BE20200728195824