why [::-3]

Question

why b is [3,0]

a=[0,1,2,3]
b = a[::-3]

Answer 1

[::-3] lets you go through the list backwards with step size 3.

The last element in a is 3. Go three steps back and you get 0. There are no elements in front of 0, so [3,0] is the whole of b.

Answer 2

but should not be [0]?

Answer 3

1) first save de initial item (-1) in this case 3
[3]
2) 3 step back is -1 -3 = -4 save -4 in this case 0
[3,0]

Answer 4

I got it! the first item is included

Answer 5

print(b)
[1]
?
a = [ 0, 1, 2, 3 ]
-4 -3 -2 -1