lists slicing

Question

sqs = [0, 1, 4, 9, 16, 25, 36, 49, 64, 81]
print(sqs[7:5:-1])

please tell me how this works

Answer 1

The formula says: return the list's elements from 7 to (but not including) 5, stepping backwards by 1.
Element index 7 is 49, next (backwards, so index 6) is 36 and that's it.

Answer 2

The code will output [49, 36] this is because the -1 says that the list should be read through backwards