Why does extended slicing not reverse the list?

Question

I\'m slicing lists in python and can\'t explain some results. Both of the following seem natural to me:

>>>[0,1,2,3,4,5][1:4:1]
[1, 2, 3]

>>>         


        

Answer 1

If you are slicing this then slicing will look like this [start:end:step]. For this one:

>>> [0,1,2,3,4,5][1:4:1]
[1, 2, 3]

It is staring from index 1 to index 3 because it exlcudes the index 4 with 1 step at a time. You are getting an empty list in the second one because you are stepping -1 from 1st index. So this will be the solution.

>>> [0,1,2,3,4,5][4:1:-1]
[4, 3, 2]

This works because you are taking an index from 4 to one with -1 step forward.

Answer 2

The third number in the slice is the step count. So, in [0,1,2,3,4,5][1:4:-1], the slicing starts at 1 and goes DOWN by 1 until it is less than 4, which is immediately is. Try doing this:

>>> [0,1,2,3,4,5][4:1:-1]
[4, 3, 2]