There is no the common interface for the "set" and "activate" methods.

Listbox.activate(index) - mandatory argument is an index (an integer, "active", "anchor", "end", or @x,y form).
Menu.activate(index) - mandatory argument is an index.
Scrollbar.activate(element=None) - optional argument is element identifier, one of "arrow1", "slider" or "arrow2".
Listbox.selection_set(self, first, last=None) - arguments are indices, first argument is mandatory.
Scale.set(value) - mandatory argument is a number between specified limits.
Scrollbar.set(first, last) - mandatory arguments are numbers between 0 and 1.