explain this code briefly

Question

list by=[1,2,3,4,5,6,7,8,9]
del list py [-3: -6: -1]
print (list_py)

Answer 1

it is a bit chaotic
list by
list py
list_py

is it all the same and simply typo?

Answer 2

The variable "list by" should be "list_by" or any alternative with no spaces.
But is a list of numbers 1 through 9. You want to delete numbers in list (which should have same variable name as above) backwards through the list starting at 7 and down to but omitting 4.
the argument in print needs the same variable name as the other two because thats the list you just worked on

Answer 3

del list_py [-3:-6:-1]
-3 = 7
-6 = 4(not inclusive stops at -5(5))
deletes [7,6,5]
Output [1,2,3,4,8,9]