An Introduction to Python Sets - Programming tutorial

Set s in Python are a type of mutable but unordered data structure, which can only contain unique elements. In other words, it is equivalent to sets in math.


set literal:

Curly brackets, {} , cannot be used to create an empty set:

>>> not_set = {}     # set constructor must be used to make empty sets.
>>> type(not_set)    # Empty curly brackets create empty dictionaries.
<class 'dict'>

You can only create an empty set by using the set() method.

>>> example_set = set()
>>> type(example_set)
<class 'set'>

However, if elements are included within the curly brackets, then it would be acceptable syntax to create a set.

>>> example_set_2 = {1, 2, 3}
>>> type(example_set_2)
<class 'set'>

Converting Iterable to Set

If set(...) contains an iterable such as a list, a string, or a tuple as an element, it will return a set containing its’ elements. This will remove all duplicate values from the list.

>>> example_set_3 = set('some string')
>>> example_set_3
{' ', 't', 'g', 'o', 'r', 'i', 's', 'e', 'n', 'm'}

If you want to convert an iterable like a list to a set, you can do that by passing it to the set() function.

>>> a = [11,2,2,6,6,4,8,9,9,7]
>>> a = set(a)
>>> print(a) # {2, 4, 6, 7, 8, 9, 11}