I am trying to make a loading and a GIF would be a lot helpful if it was supported in python tkinter. But since it is not supported, so I put all the frame-by-frame pictures in the list that makes a loading when played continuously (using assign_pic function) and then I created a label (called lab_loading) of which I change the picture after 200ms by calling the start_anim function. I am calling the assign_pic function in a loop which I think causes this error. See my source code below