I know that Python has built-in list functions but I'm curious as to how one would write a function to sum a list and a function to reverse a list. I was able to figure out how to write some other list functions (`sort`, `count`, `index`, etc.) but not these, and I imagine some other languages don't have these built-in functions.

Could someone show me some Python code for those 2 functions, not using any other built-in functions?