slicing insert question, L[1:1]

Question

practising some python, which is a pretty easy language to grab up.

I have

>>> L = [1,2,3,4]
>>> L[1:1] = [1,2,3]
>>> L
[1, 1, 2, 3, 2, 3, 4]

so on line two actually L[1:1] is empty list, but how can python understand that insert the [1,2,3] list to starting from 1. I guess there is some internals which is not transparent to us, here apparently, I guess L[1:1] returns a reference to index 1 even if that returns an empty list...

Best wishes, Umut

Answer 1

L[1:1] means the slice of the list L starting at index 1 (the second element), up to but not including index 1. So it is an empty list. On the right-hand side of an assignment, it is simply an anonymous empty list. But on the left-hand side, the assignment knows where the slice has been made, and can splice in the new list value into the proper place.