A set is used to contain an unordered collection of objects. Unlike lists and tuples, sets are unordered and cannot be indexed by numbers. But there is one character that makes sets standout and useful: the elements of a set are never duplicated. Imagine if you have a list of IPs that you need to put in an access list of. The only problem in this list of IPs is that they are full of duplicates. Now, think about how you would use a loop to sort it out for the unique items, the set built-in type would allow you to eliminate the duplicate entries with just one line of code. To be honest, I do not use set that much, but when I need it, I am always very thankful this exists. Once the set or sets are created, they can be compared with each other ones using the union, intersection, and differences:

    >>> a = "hello"
    >>> set(a)
    {'h', 'l', 'o', 'e'}
    >>> b = set([1, 1, 2, 2, 3, 3, 4, 4])
    >>> b
    {1, 2, 3, 4}
    >>> b.add(5)
    >>> b
    {1, 2, 3, 4, 5}
    >>> b.update(['a', 'a', 'b', 'b'])
    >>> b
    {1, 2, 3, 4, 5, 'b', 'a'}
    >>> a = set([1, 2, 3, 4, 5])
    >>> b = set([4, 5, 6, 7, 8])
    >>> a.intersection(b)
    {4, 5}
    >>> a.union(b)
    {1, 2, 3, 4, 5, 6, 7, 8}
    >>> 1 *
    {1, 2, 3}
    >>>