> Take lists: some operations are methods, some are functions, some mutate the list, some make a copy, some are global, some are in a module.

Let's take the list type, the public methods are: 'clear', 'copy', 'count', 'extend', 'index', 'insert', 'pop', 'remove', 'reverse', 'sort'

Obviously as the names imply `copy` returns a new list, and `count` returns an integer. Neither mutate the list.

For the rest of it: methods mutate the list. There are some builtin functions that do similar things, but those always a new object (sorted, reversed)