Logic behind Python slicing

Question

Hi everyone,

while doing some challenges, I came across a code that looked like this :

x = [1, 3, 4, 5]
print(x[:1:-1])

The output is [5, 4], and if we replace the -1 by -2, -3 or even -8500, the output will always be [5].

Can someone help me understand the logic behind this slicing please ? Thank you for your time

Answer 1

x[start:firstnot:step]
start default is 0 or most left if step is negative.
if step is <0 we go from right

so start at 5 and firstnot is 3.
step - 1: 4
as u mentioned [5,4]

but step - 2:3
but 3 is already out of scope:[5]

same for all steps - 2,-3,...,-5000

Answer 2

Thank you for the answers, it is very clear now !