Add duplicates to a set or check if the elements exists then add

Question

Using sets in python, I want to add many items to my set, some of which probably already exist in that set.

Is it faster to add items to a set without checking if it's already there, or is it faster to check if each item exists in the set already and only add if it isn't there?

Answer 1

It's faster to add without checking. Every time you add an item to a set it needs to check that the item isn't there - Checking before is not saving you any time if the item is there, but it is wasting time if it isn't there as it will be checked twice.