TypeError: list indices must be integers or slices, not NoneType

Windows 10

I would like to present two grating stimuli that vary in orientation and opacity each trial in a randomized loop. The one on the left is called patchLeft The one on the right is call patchRight. The participant will be asked about either the orientation or the opacity (ex: which patch leans further to the right?), and will have a chance to respond. The orientation and opacity used will be different for each participant, and will be entered prior to each experiment into the code like this:

contr_set = [0.6, 1]
ori_set = [45, -45]

In order to have the correct question and response correspond to the correct contrast or orientation I made a spreadsheet to use as the loop parameters. In the sheet I have 6 parameters: [contrLeft, contrRight, oriLeft, oriRight, whichQuestion, corrAns]

contrLeft, contrRight, oriLeft, oriRight are all values of either 1 or 0. So for patchLeft I enter ori_set[oriLeft] in the orientation box, and contr_set[contrLeft] in the opacity box. The same is done for patchRight except as ori_set[oriRight] and contr_set[contrRight].

I believe what this should do is to choose the given value from the list (at either position 1 or 0) and set that value as the opacity or orientation.

Running the experiment, it works as it should but randomly (since it is a random loop) will throw the error:

TypeError: list indices must be integers or slices, not NoneType

This is always because of patchLeft.setOpacity(contr_set[contrLeft])

I do not think it is the spread sheet itself because when I went through it sequentially once, it only threw the error after going through every variation I had listed.
I was wondering if it is because contr_set[contrLeft] is a float, but then why would it not throw the code for any other times that float is invoked.
My best guess at this point is that I am not calling the item from the list correctly, or am misunderstanding what I am actually doing the way I have it currently setup.

Any help would be appreciated.

What do you have in Selected Rows?

Do you have any blank cells in your spreadsheet?

It was reading the last blank row, I specified 0:32 when it was defaulting to 34. contrLeft is the first column which now makes a lot of sense. Thank you!