difference between lists and sets

Question

Are there any other difference between sets and lists in Python other than the use of the union, intersect, difference, symmetric difference functions to compare two sets? Why can't these functions simply be applied to lists? In what situations are sets more useful than lists?

Answer 1

There are a lot more differences such as :

1. Sets can't contain duplicates
2. Sets are unordered
3. In order to find an element in a set, a hash lookup is used (which is why sets are unordered). This makes __contains__ (in operator) a lot more efficient for sets than lists.
4. Sets can only contain hashable items.
 

In practical applications, lists are very nice to sort and have order while sets are nice to use when you don't want duplicates and don't care about order.