I am confused When we do list slicing, can we use first value negative? If not then why? Can someone please explain this to me?

Question

Eg. List=[0,2,4,7,8,9,5,7,1]
Slice= List[-2:1:1]

Answer 1

Yes, any of the values can be negative.

List[-2:1:1] is a shortcut for List[len(List) - 2:1:1].

Because it tells to slice from index 7 (9-2) to index 1 with the step of 1, which is impossible, the slicing gives an empty list.

Answer 2

Thank you guys Seb TheS , G B , 𝐊𝐢𝐢𝐛𝐨 𝐆𝐡𝐚𝐲𝐚𝐥 for the explanation. It helps me to understand more.

Answer 3

the syntax is: list[start, stop, step]

if you want to go backwards, lets try from the code you provided.

List[5:0:-1]
# output
[8, 7, 4, 2]

Answer 4

When slicing, the last number gives the step. If it is positive, it goes from left to right, if it is negative, it goes from right to left...

List[-2:1:-1] #output [7,5,9,8,7,4]
List[-5:-2:1] #output[8,9,5]

these are also possible , when first number is negative...