Towers of Hanoi get_input Function

I’ve got up to Step 28 of Towers of Hanoi, and my get_input() function has suddenly started glitching. Whenever I try to run my code, it throws the following error:
Towers of Hanoi Error
I checked the offending line of code, but it matches what the project’s video recommends perfectly near as I can tell. Just in case I’m wrong, here it is:

choices = [stack.get_name()[0] for stack in stacks]

I hope someone can help me with this!

Never mind! I found my problem.