Python list slicing exercise doesn't make sense

Question

I understand that the [start:end] notation means the first number is the position in the list where the slicing start and the last number is the position -1 in the list where the slicing ends, but in this example

 U= [2, 'haha', [5,6,9], 3, 2, 1] ; 
 U[1:2]=[] ; 
 U[2:]=[] ;

The resulting slice is:

 U= [2, [5,6,9]]

Why is this the answer? I get that in the second step 3,2,1 gets eliminated. But why is the resulting slice [2,[5,6,9]] and not [5,6,9]

Answer 1

Python list slices can be replaced by iterables.

You start with this:

U = [2, 'haha', [5,6,9], 3, 2, 1] ; 

U[1:2] is 'haha' (From element 1 up-to-but-not-including 2 ), so replacing that with an empty iterable [] essentially removes 'haha' from the list.

At that point, you have [2, [5,6,9], 3, 2, 1] .

U[2:] is from element index 2 to the end, which is [3, 2, 1] . Again, as before, setting this to the empty iterable [] , deletes these three elements, leaving [2, [5,6,9]]

Answer 2

Using the python console may make the example easier to understand:

>>> U = [2, 'haha', [5, 6, 9], 3, 2, 1]
>>> U
[2, 'haha', [5, 6, 9], 3, 2, 1]

Get rid of second element.

>>> U[1:2]=[]
>>> U
[2, [5, 6, 9], 3, 2, 1]

Get rid of everything past the second element.

>>> U[2:] = [];
>>> U
[2, [5, 6, 9]]