Sets are unordered collections of elements. You cannot access specific elements using an index or a key. The only way to access items in a set is by using a for loop, or by testing for the existence of elements in the set using the in operator.

You have to think of sets in the mathematical sense. In mathematics, a set is a collection of elements, all unique, and elements can be part of a specific set, or not part of the set. You use special set operators to combine sets in different ways.

Python uses dictionaries to implement sets; specifically, it implements the elements of a set as dictionary keys. Thus, only immutable data types can be set elements. Sets themselves, however, are mutable.

Since Python uses dictionaries to implement sets, you might think that you can create an empty set by assigning {} to a variable. That, however, does not work as it creates an empty dictionary, not an empty set. Instead, you create an empty set by assigning a call to the function set() to a variable.

To create a set with some elements already in it, you can assign the elements to the variable between curly brackets. Alternatively, you can call the set() function with a list of the elements as argument.

fruitset = { "apple", "banana", "cherry" }
print( fruitset )

If you want to create a set consisting of the different characters in a string, you can call set() with the string as argument.

helloset = set( "hello world" )
print( helloset )

You can use a for loop to traverse a set. The variable in the for loop gets access to all the set elements. There is no way to determine in which order you get to see the elements. Sorting them is not possible as long as they form a set. You can, however, use list casting on a set to create a list of its elements, which can then be sorted.

fruitset = { "apple", "banana", "cherry", "durian", "mango" }
for element in fruitset:
    print( element )
print()

fruitlist = list( fruitset )
fruitlist.sort()
for element in fruitlist:
    print( element )

You can determine the number of elements in a set using the len() function.