Beg god gives directions of all stripes, is the whole collapse in this experiment,

I was made of the psychopy psychology experiments, one of the steps (five pictures showing the random) seems to require randint function, I write all five photos into the Excel, the Excel imported the experiment, the wish to generate random a number from 1 to 5, as long as the code is no problem, the experiment should be able to render the number represented by the picture, but I have been wrong code, display NoneType object is not iterable. This is how to return a responsibility? Want to ask you I wrote a code, the screenshot below, thank you!