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Python Sets

Published Dec 20 2020

Sets are another important Python data structure.

We can say they work like tuples, but they are not ordered, and they are mutable. Or we can say they work like dictionaries, but they don’t have keys.

They also have an immutable version, called frozenset.

You can create a set using this syntax:

names = {"Roger", "Syd"}

Sets work well when you think about them as mathematical sets.

You can intersect two sets:

set1 = {"Roger", "Syd"}
set2 = {"Roger"}

intersect = set1 & set2 #{'Roger'}

You can create a union of two sets:

set1 = {"Roger", "Syd"}
set2 = {"Luna"}

union = set1 | set2
#{'Syd', 'Luna', 'Roger'}

You can get the difference between two sets:

set1 = {"Roger", "Syd"}
set2 = {"Roger"}

difference = set1 - set2 #{'Syd'}

You can check if a set is a superset of another (and of course if a set is a subset of another)

set1 = {"Roger", "Syd"}
set2 = {"Roger"}

isSuperset = set1 > set2 # True

You can count the items in a set with the len() global function:

names = {"Roger", "Syd"}
len(names) # 2

You can get a list from the items in a set by passing the set to the list() constructor:

names = {"Roger", "Syd"}
list(names) #['Syd', 'Roger']

You can check if an item is contained into a set with the in operator:

print("Roger" in names) # True


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