Sets (sets)

A set() is a collection of unchangeable and unique elements - just as in the mathematical sense. In a sense, it is a list that does not allow duplicates. It can be created from an iterable container, e.g. a list or a tuple. Entries in a set must in turn be immutable.

set([1, 1, 0]) # Returns {0, 1}

A non-empty set can also be created directly with curly brackets {...}. An empty set cannot be created in this way because this syntax is already reserved for the dictionary. Here, set() must be used.

{1, 2, 3}

There are a number of operations for sets:

Operation	Description	Example	Result
len(s)	Number of elements	len({1, 2, 3})	3
x in s	Checks whether x is contained in s	2 in {1, 2, 3}	True
x not in s	Checks whether x is not contained in s	2 not in {1, 2, 3}	False
s | t	Union of s and t	{1, 2} | {2, 3}	{1, 2, 3}
s & t	Intersection of s and t	{1, 2} & {2, 3}	{2}
s - t	Difference set of s and t	{1, 2} - {2, 3}	{1}
s ^ t	Symmetric difference set of s and t	{1, 2} ^ {2, 3}	{1, 3}
s <= t	Checks whether s is a subset of t	{1, 2} <= {1, 2, 3}	True
s >= t	Checks whether s is a superset of t	{1, 2, 3} >= {1, 2}	True

If you find the operator notation confusing, you can also use the method notation:

Operation	Description	Example	Result
s.issubset(t)	Checks whether s is a subset of t	{1, 2}.issubset({1, 2, 3})	True
s.issuperset(t)	Checks whether s is a superset of t	{1, 2, 3}.issuperset({1, 2})	True
s.union(t)	Union of s and t	{1, 2}.union({2, 3})	{1, 2, 3}
s.intersection(t)	Intersection of s and t	{1, 2}.intersection({2, 3})	{2}
s.difference(t)	Difference set of s and t	{1, 2}.difference({2, 3})	{1}
s.symmetric_difference(t)	Symmetric difference set of s and t	{1, 2}.symmetric_difference({2, 3})	{1, 3}