Please how does this code snippet work?

Question

a = [0,1,2,3,]
for a[-1] in a:
print(a[-1])

It outputs 0,1,2,2 but I don't understand why. I thought it should output an Error but I was wrong.

Answer 1

a[-1] means last element in the list.

for i in a is storing each element of a in temporary variable i when looping.

for a[-1] is storing each element of a in the last slot of a. So the last element has the value of second last element when the loop reaches the last slot.

https://code.sololearn.com/cjTMp4kCULX8/?ref=app

This quiz is for brain teasing only. This is something you will avoid doing in actual programming.

Answer 2

This seems like magic to me too at first glance. After playing around, I think the real magic is the line:
for a[-1] in a:
This line loop through the value in a array, assign each value to a[-1] in each loop, and print out the a[-1]
Breakdown :
a[-1] = a[0] = 0
a[-1] = a[1] = 1
a[-1] = a[2] = 2
a[-1] = a[-1] = 2

Answer 3

I understand better now. Thank you both for your answers!