Just my_list[4:end]? Ok, I get you want to pull out the 4:end to re-use it, but note that there is zero cost to constructing that thing. Unlike Python, our : range syntax works outside of indexing. You can just do my_boring_slice = 3:3:8 or my_interesting_slice = 4:length(my_list) or even my_whole_dimension = (:).
Julia’s slices are just arrays of integers. That’s it. There is a very simple package that you can use — EndpointRanges.jl — that can give you an end that works outside of indexing and dynamically matches the arrays it indexes into.